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WateringBuffalograss seeds, why so much water?
Irises, how much water
Irrigation backflow prevention
Irrigating tree with pipe in the ground
Passive water harvesting
Plastic, pipes prevent thorough watering
Soil moisture depth
Trees need water in winter
Using water softener "purge" to water
Vegetable garden irrigation
Water for fruit tree, how much?
Water from above or below?
Water softener bad for plants
Watering after rainfall
Watering, does it burn plants?
Watering through bark
Watering trees and lawn
Watering trees through winter
Watering while away from home
Winter irrigation, how much
Black plastic & pipes prevent thorough watering 6-98
Q. I hired a man to remove my lawn and plant a xeriscape for me. He has covered the soil with black plastic to prevent weeds, except for a small area inside a ring of rocks around my two large ash trees. The trees have been here about 15 years and are important for shading our house in the afternoon. To provide for watering the trees, he did not put plastic in the rings around the trees. These rings are about six feet across. Then to be sure we could water the trees deeply, he place a piece of pipe into the ground about three-feet deep and about 18 inches from the trunk of each tree. He told us to be sure to water the trees by filling the pipe every two weeks. Is every two weeks often enough to water the trees?
A: Here in New Mexico, in all but the sandiest soils, irrigating an established tree every two weeks in the summer and once a month in the winter should be adequate. However, the frequency of the irrigation is not the important factor in your case. You should be concerned about where you apply the irrigation water.
The pipe in the ground will place the water below the level of the majority of the absorbing roots, those responsible for absorbing the water and mineral nutrients needed by the trees. Most people are surprised at the shallow depth of tree roots. The majority of the absorbing roots of trees are in the top six to twelve inches of the soil. Some absorbing roots will extend down to a depth of about three feet, but the pipes placed at the base of your trees start irrigating at three feet, below the level of the ash tree roots. While ash trees can have deeper roots, in our soils and dry climate there are few roots below the two- to-three-foot depth in the soil.
The second problem I see in what you described is the fact that you are watering at only one point for each tree. A tree has an extensive, spreading root system which is necessary to extract sufficient water and mineral nutrients from the soil. A wide spreading roots system is also necessary to support the tree in strong winds, which we experience here in New Mexico. To adequately supply irrigation water to a tree, it is necessary to provide water to most of this root system. That is, you must water a large area, not just one spot. So the pipe is a bad idea because of the depth, which is below most of the absorbing roots, and the location which waters only a small portion of the roots.
Another, and very critical, consideration is the fact that the active, absorbing portion of the root system is the system of very small, fine roots at the ends of the larger roots. Watering at the pipe, only a foot and a half from the base of the tree, applies the water to only the big, supporting roots (and below them at that), not to the fine, absorbing roots. The large roots do not absorb, and water at that location may increase the likelihood of termite, carpenter ant, or fungus damage to these roots.
The black plastic which has been placed under the rocks in the landscape prevents rain and snow melt from entering the soil at the location of the critical, absorbing, root system. It also restricts the diffusion of oxygen, needed by roots into the soil. A porous weed barrier doesn’t cause this problem and is definitely preferable to the impermeable black plastic. However, in our windy, dusty environment, dust accumulates above any weed barrier fabric, even the porous fabrics, and weeds often begin growing in this dust when there is sufficient moisture. If the roots of these weeds penetrate the pores of the weed barrier, it is very difficult to remove them by pulling. In such a case, herbicides become the most feasible means of managing the weeds.
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Does watering burn plants?
Q. Now that hot weather has arrived, people are being urged not to water during the day. The most obvious reason is to reduce evaporation and blow off. Yet, I continue to hear comments that watering during the day will burn your plants. Reasons sited - water droplets act to magnify solar intensity and that water is the best source for heat conduction (this from a fireman). Does water really burn the plants? It doesn't seem likely.
A. I don't think the water drop can be a magnifier. The focal point of this shape lens (plano-convex) is considerably below the leaf. As the drop gets smaller, the point of focus will move, but then less light is collected. So, I don't accept the magnifying glass hypothesis.
The heat conduction hypothesis is one I haven't heard before. However, I also doubt this one. The water must have a source of heat from which to conduct the heat. My question is - conducting from where and what? It can only be conducting heat from the air which is not hot enough to burn the plant. The rest of the leaf where there is no water is in direct contact with the rest of the air. In fact, the water evaporates and cools, so the spot with the drop is cooler than the rest of the leaf (though not by much). In cool weather, this cooling may perhaps cause some problems as it lowers the temperature of a small area of the leaf while the rest of the leaf is warm and active.
Perhaps the deposition of salt could explain some burning. This is especially true if there is fertilizer salts in the water. As the water evaporates, the various mineral salts which are so prevalent in our water may concentrate to a level that may cause problems. As the solution outside the cells increases in salt concentration (as the water evaporates), the water may osmotically draw water from the leaf cells, causing injury to the cells. After all, rain doesn't wait for night-time to fall, and I don't recall seeing leaf injury from raindrops unless there was hail associated with the rain. Evaporation and misapplication of water during the day are probably the best answers to the "why not water in the day" question.
So, the best reasons for not watering in the day, and especially for not watering in the afternoon, is that the winds are strongest in the afternoon and evaporation is greatest due to heat in the afternoon. The coolest time of day, when evaporation rates are lowest, is in the early morning. The stillest time of the day in New Mexico is the morning, so water goes where it is supposed to go and less evaporates in the wind in the early morning.
A final reason for watering in the early morning is that the crown of the plant dries during the day, while the water deeper in the soil remains longer. By allowing the crown of the grass to dry, fungal problems are avoided. This is also improved by not watering every day. If you water deeply (assuming soil prepared by rototilling to a depth of eight or more inches), it is not necessary to water daily and fungi will be less able to infect your lawn.
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How much water for fruit tree? 7-99
Q. I planted a semi-dwarf Elberta peach about 6 or 7 years ago. Every year we get about the same number of peaches (25-30). They are good quality. However, the tree has not grown more than a couple of inches since we planted it. It leafs out normally, the branches grow an inch or two and stop growing. I water once a month in the winter, once a week in the spring and fall, and twice a week in the summer. I use a liquid, spray-on fertilizer just before and during its expected growth, yet it doesn’t grow. Please help me and my tree.
A. Because your tree is a semi-dwarf peach, it will grow more slowly that standard-size peaches. The production of fruit also limits its growth. If you would like to see more growth, you might try removing at least half the fruit in May next year. Fertilizer with a high nitrogen analysis will also stimulate vegetative growth (at the expense of fruit production), but don’t apply such fertilizer after mid-July. Applying nitrogen too late may stimulate growth which has not hardened for winter before your first frost.
Your watering schedule seems adequate, or perhaps too often, but your watering frequency should be determined by your soil type. How much water do you apply with each irrigation? It is important to apply water equivalent to about 80% of evaporation-transpiration (ET - water evaporated from a wet surface and transpired through plants). The potential ET rate is determined by measuring water evaporated from a standard evaporation pan. This data is available on the Weather Page of the NMSU/College of Agriculture World Wide Web Page. (This page, http://weather.nmsu.edu, is maintained by Dr. Sammis at NMSU
The quantity of water to apply should be 80% of that reported as evaporated (in inches) times the area of the absorptive root system times the number of days since the last irrigation. The area of the root system is (for your tree) probably a circle with a 5 to 10 foot radius around the tree. The water should be applied over this entire area (except for about a 1 to 2 foot radius next to the trunk). Since only the surface dries quickly, deeper water remains longer, so watering once a week or less should be all that is required. The soil type determines the frequency of irrigation because sandy soils hold less water than clay and should be watered more often. You can determine when to irrigate by probing the soil with a screw driver (long blade) about 3 to 5 feet from the trunk. After withdrawing the screw driver from the soil, feel the blade. If it is dry (not cool), it is time to irrigate. If the blade is cool or you can feel moisture, you can wait to irrigate. Test a few days later. It may take a few weeks for the tree’s root system to adapt to a new irrigation schedule, so change gradually.
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Irrigating tree with pipe in the ground 6-01
Q. I have two 2"x12" PVC pipes buried at the drip-line of each tree I have planted in my yard, with holes drilled in the side of the pipes and small rocks in the pipes. I have drippers in each pipe. This is how I water my trees. May I administer properly diluted chelated iron directly into the PVC pipes rather than pouring it on the ground around the tree? Is it possible to use these PVC pipes as a way to administer fertilizer, etc. - pouring it down the PVC pipe rather than just on the ground? I’m wondering if this would get help directly to the roots rather than on the grass around the tree?
A. I have heard of this technique since I was a child. There is some logic to the technique - the water is placed below the surface and less subject to evaporation. However, there are problems with this technique as well. You have largely avoided the first problem by not using a longer pipe. Even a pipe that is one-foot long has you watering below many of the roots. If the pipe was perforated and the drip emitters provided water fast enough to fill the pipe, it would help by allowing some water to escape at different depths.
A second problem is the number of pipes. You have used two, but many more would be better. The larger the tree, the greater the root system. Most of the roots that actively absorb water and nutrients are further from the tree than the dripline. With only two pipes at the dripline, you are providing water to a very small percentage of the root system. If the pipes have been in place since the tree was first planted, the tree may have developed its root system only where the pipes provide water. This is especially true if there is never moisture in the soil at any other location. Nevertheless, the root system is quite limited in this circumstance. At least four to six pipes equally spaced around the tree (at and beyond the dripline) would encourage development of a more extensive root system. If the soil is sandy, the water will quickly permeate the soil downward, spreading very little laterally. Once the water has permeated the soil to a depth greater than three feet, much of the water is unavailable to the tree and is wasted. A loam or clay soil will allow more lateral movement of the water and less rapid loss of the water below the trees root zone.
If you use this system of irrigation, the soil type will determine the number of pipes needed. The lack of distribution will create a problem with the application of nutrients about which you asked. The nutrients will be localized, and there is a possibility of damage to the limited root system when fertilizer is applied to the roots through the pipes. (The chelated iron should not cause damage.) Properly diluted fertilizer will not damage the roots, but remember that the instructions for dilution are not designed for application in this manner. Those directions may allow for too highly concentrated nutrients. If lawn irrigation or rainfall has allowed development of roots outside the zone supplied by the pipes, then you will be providing nutrients to only a small portion of the root system and the effects will be less than desired. Be careful fertilizing your tree in this manner.
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Irrigation system backflow preventers
Q. I just had a new irrigation system installed in my landscape. They put in some pipes that stick up in the air. I am afraid that the water in these pipes will freeze. Why did they do that?
A. According to Willie West, licensed irrigation contractor and member of the New Mexico Irrigation Association, the pipes you describe sticking out of the ground are the backflow preventers which prevent contamination of the city water supply and the water you drink in your home from contamination by water from the landscape which may contain fertilizers or pesticides.
Willie points out that this protection is provided only if the system is installed properly. He says that unfortunately there are many ways to install the backflow preventers improperly. If they are installed properly, they provide protection and most of the backflow preventer types will not require winterizing.
A properly installed system consists of below-ground valves, positioned below the depth of frost in the soil with the backflow preventer positioned "downstream" from the valves so that water drains from them when the valves close. For this to happen, it is important that the all-metal (brass, copper, and galvanized pipe) backflow preventer be elevated higher than the highest point of use; that is, the backflow preventer must be above the highest sprinkler head or drip emitter. If this is not the case, the backflow preventer is improperly installed and is subject to winter damage failure in its purpose of protecting your water supply. This requirement that it be above the highest point of use explains why these pipes are above the ground.
If your have any other questions or problems regarding your backflow prevention device or any other part of your irrigation system, please contact a properly licensed and insured irrigation contractor.
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Passive water harvesting
Q. What is "passive water harvesting"? I have been collecting rainwater from my roof for years in large barrels, so I understand "water harvesting", but I'm not sure what is meant by "passive" water harvesting.
A. Passive water harvesting, like passive solar energy utilization, tends to be a system of water harvesting requiring little energy input and little effort on the part of the gardener after the system is constructed.
This method of water harvesting doesn't involve collection barrels and should have less need for screening and chemicals to prevent mosquitoes and other pests breeding in the harvested water. Water from rooftops and other hardscape areas of the landscape are directed into storage in the soil. This water is applied to trees needing deep irrigation and to areas needing leaching to remove salts that accumulated after application of poor quality water. There is no need for pumping or transporting the water from the storage site to the point of utilization. It is utilized at the storage site.
Water from the rooftop and other areas is directed by a system of swales (broad shallow ditches) to the area where it will be utilized. The soil is then distributed across that area and seeps into the soil. Water on the surface may evaporate, but the deeper water will be utilized by trees and other deeply rooted plants in the area.
The system of swales may be a shallow, almost unnoticeable, linear depression in a lawn area, or it may be a mock arroyo lined with plastic and filled with cobbles and boulders to become a distinctive element in the landscape. The arroyo may be landscaped with appropriate plants within this arroyo or plants may line its margin. The main purpose is to direct the water from near the house to a point of usage away from the foundation and among plants needing deeper irrigation.
Passive water harvesting may not provide all the irrigation needed by trees in the landscape, but will reduce the need for purchased or pumped water, reducing costs for maintaining the trees. An interesting fact, long apparent to gardeners, is that rain water is better for plants than tap water. There is no reason to waste rainwater by allowing it to runoff. It is also a waste to allow rainwater to seep deeply into soil with shallow rooted plants. It is best used with the deeper rooted plants in the landscape.
Passive water harvesting does compete with "active water harvesting" in which water is collected in barrels to be distributed by pumping or gravity drainage at a later date. Gardeners should determine which system is most appropriate for their landscape. If the vegetable or flower garden is the place most in need of harvested rain water, then the active water harvesting system will be more appropriate. Other gardeners will find that passive water harvesting is most appropriate for them and provides an opportunity for creating an interesting element in the landscape. Either system allows gardeners to make best use of the (usually) sparse rainfall of the Southwestern U.S.
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Proper watering key to vegetable production
By George W. Dickerson
The Melon Patch, June 2001
As hot, dry weather begins to stress home gardens in June, proper watering is critical for healthy young vegetable plants and quality produce.
Watering is both a science and an art. Gardeners should learn to spot signs of water stress on plants. Water-stressed lettuce can be bitter, for example, while tomatoes and chile will often develop dead patches at the tips called blossom end rot. Water-stressed chile also tends to become more pungent, although over watering it can also increase incidence of chile wilt. Water-stressed sweet corn, meanwhile, can be poorly pollinated with fewer kernels on the ear.
To prevent problems, keep shallow-planted vegetable seeds moist until after the plants emerge. Thereafter, water less frequently but deeper, wetting the soil at least 12 inches below the surface. Allow surface soil to dry out between irrigations to promote deeper root growth and more drought-tolerant plants. Applying organic mulch like dry bluegrass clippings, straw or old hay will reduce evaporation. Mulches will also cut down weed problems. Sprinkler irrigation is popular among gardeners, but it’s very wasteful, especially in windy weather. Salts in most tap water can crust the soil, hindering emergence of small-seeded crops. Sprinkler systems can also damage tomato fruit during the summer, causing them to crack.
Gardeners using sprinklers should irrigate early in the morning to allow plants like squash to dry out in the afternoon to reduce powdery mildew and other foliar diseases. Furrow irrigation is also popular in New Mexico. Plant vegetables on the outside edges of raised flat vegetable beds, allowing water to soak inward toward the middle of the bed. This will concentrate salts in the water and soil in the center, away from plants. Never let water run over the top of the bed because it can cause the soil to crust.
Drip irrigation is the most efficient water technique. Place drip lines near the plants so water moves evenly out away from the base, concentrating salts away from the plants. The garden can occasionally be flood irrigated to wash accumulated salts below the roots. Drip irrigation, however, is often expensive and complicated. Regulators may be needed to reduce pressure on the lines, and filters are often used to keep soil from clogging the lines. More expensive systems can include fertilizer injectors.
For more information on watering techniques, visit New Mexico State University’s Cooperative Extension Service publications world wide web site at http://www.cahe.nmsu.edu/pubs/_h. George W. Dickerson, Ph.D., is a horticulturist with New Mexico State University’s Cooperative Extension Service.
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Trees need water in winter too
Q. I planted several young trees this summer and have tried to be diligent in watering them. My question is what kind of watering schedule would generally be appropriate for the fall and winter months? (The trees in question are Sycamore, Arizona Ash, and Chinese Pistache.)
A. In the fall and winter when temperatures decline and as leaves drop from deciduous trees, the rate that water is used by the trees decreases. We can reduce the frequency of watering at this time. Continue to apply the same amount of water with each irrigation, just apply water less often. The frequency with which you irrigate will depend on the age of the trees, the soil in which they are planted, and weather conditions. Remember that evergreen trees have retained their leaves and will need to be watered as well. Young trees have less extensive root systems and should be watered every 14 to 20 days if there has been no soaking precipitation.
Older trees, established for three or more years, can be watered every 20 to 30 days. The more frequent irrigation, 14 or 20 days depending on tree age, is required for trees growing in sandy soils which hold less water. Longer intervals may be allowed for trees in heavier soils containing clay. If the weather has been warm and windy, additional irrigations may be needed. If the weather is cool and there have been good slow, soaking, rains or snows, irrigations may be skipped. Check the soil to see if there is moisture several inches down. While you don't want the soil to dry totally, there is little reason to apply water while the soil is moist. In areas where the soil freezes, it is difficult to add moisture. In these areas, irrigate well before the soil freezes and when it thaws.
When irrigating trees, moisten the soil to a depth of two to three feet with each irrigation. This should then provide sufficient water to keep the soil moist for the intervals recommended above. Remember, a clay soil will hold more water than sand, so you must apply more water to moisten clay to the same depth than when watering sandy soil. Since clay soils absorb water slowly, you may have to irrigate very slowly or in several brief, repeated, irrigations to provide enough water to moisten the soil to the proper depth. Water applied too rapidly to clay runs off and does not accomplish your purpose.
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Using water softener "purge" to water 9-02
Q. We recently installed an "Ecowater" water softener. We had the effluent (potassium salt water) drained to the outside so we could use it. We were told it would not hurt the trees. Is this true? We get a purge of about 30 gallons every four or five days. We hate to waste the water. Should we use it or drain it down the sewer?
A. Whether or not to be concerned depends on your soil conditions. In the East where soils are acidic and deficient in many mineral salts, the potassium in the water would be beneficial. In Southwestern soils, such as those in New Mexico, there is reason for concern any time we add additional salts to already salty soils (potassium is a nutrient salt, but it is a salt). The only way to be sure is to have your soil and the effluent from the water softener tested for quantity of dissolved solids (saltiness). Your local Cooperative Extension Service office can help you get your soil tested and help you interpret the results.
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Water softener bad for plants 5-99
Q. Is it true that water from my water softener is damaging my plants? A friend told me that the reason I can't grow houseplants is because I have a water softener.
A. Your friend may be correct. While there are many factors which make growing houseplants difficult, softened water can indeed be a cause of problems. If your water softener replaces calcium and other hard water minerals with sodium, a common means of softening water, then it is indeed causing problems when you water your plants with that water. Sodium, though needed by some plants in very low amounts, is toxic to plants at slightly higher concentrations. As you water the plant and the water is used by the plant, the sodium enters the plant. As the water evaporates from the soil, the sodium concentrates in the soil. Over time, the concentration of sodium causes the problem to get worse as sodium levels increase. There are potassium-based water softening systems which may cause less problems. In these systems the hard water minerals are replaced by potassium, a plant nutrient that is beneficial to plants. However, as the potassium accumulates in the potting soil, it too can reach levels which are damaging. Potassium can accumulate to higher levels before the problems develop. Proper leaching of salts (potassium and other salts) from the potting soil frequently, and repotting before injury occurs, are ways to have softened water and avoid the problems.
There are other methods of removing hard water minerals from soil. As long as plant toxic minerals are not added to the water, they should cause no problems. In many cases the easiest solution is to just use water from a faucet that receives unsoftened water. In New Mexico ground water usually has high mineral content, but only in some areas is the content high enough to cause plant injury. However, leaching the salts from the soil on a regular schedule is important.
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Watering after rainfall? 7-99
Q. We have begun to get some rain. Can I stop watering my lawn at least for a week or so?
A. Whether or not you need to continue to irrigate your lawn depends on how much water the soil in your lawn has absorbed. If the rain falls rapidly and run-off occurs, then there was little water absorbed into the soil. This will be worse if the ground is not level and the water easily runs off. You should check the depth of moist soil to determine if you need to irrigate. Use a long screw driver, shovel, or other metal probe to test soil for soil moisture. If the soil is moist six or more inches deep, the probe will penetrate the soil easily to the depth of the moist soil. If the soil is moist to a depth of at least four inches, you can dispense with irrigation for that day. If you have an automatic irrigation system that runs regularly and keeps the soil moist, it would be wise to skip one or two irrigations.
From this, don't think that four inches is the ideal depth of irrigation. Grass roots can reach greater depths in properly prepared soil (by rototilling deeply). The greater the depth of roots in the soil, the more efficiently you may irrigate and the less subject the root system is to drying and temperature damage.
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Q. I'm puzzled. I heard that some plants should be watered from above and others from below. Which plants are in which category?
A. Many people think that they should water African violets and some other hairy-leafed plants from below to prevent spotting of the leaves. I have not had a problem with this in any of my African violets, perhaps because our very dry air allows drying before disease has a chance to develop. I think this is one of the gardening concerns brought to the Southwest from other regions where growing conditions are different.
Here in the southwestern U.S., we have different concerns. One of the primary concerns when growing potted plants is the accumulation of salts in the soil. These salts are not the familiar table salt (sodium chloride), although that salt is possible. The salts we are concerned with are more likely to be compounds containing calcium, which is present in our well waters and our southwestern soils.
Accumulation of salts can cause root damage and death of the plant. Irrigating potted plants from below can cause rapid accumulation of salts in the pot. However, improper irrigation from above can also cause salt accumulation problems.
There are instances when watering from below is beneficial. Soaking from below is especially helpful in wetting a soil that has dried so much that it does not absorb water applied from above. Such soils often have cracks that allow water to flow through quickly without wetting the soil, or the soil has pulled away from the side of the pot, allowing water to run around the soil without wetting it.
To prevent accumulation of salt, water must drain from soil after irrigation to "leach" away dissolved salts. This is true whether the plant is watered from above or below. Gardeners often place a dish under the flower pot to protect furniture from leachate water, but if this water is allowed to re-absorb into the pot, the leached salts accumulate in the soil. Place the bottom of the pot above the level of accumulated leachate water by adding a layer of gravel to the dish under the pot to prevent re-absorption of water, or pour away the leachate after watering.
If it is necessary to water from below to moisten dry soil, allow surplus water to drain away after the soil has moistened. This can be done by removing the pot from the container of water and placing it over a drain rack in an empty container or by placing the pot into a sink or bathtub so that the water freely drains away.
Late winter and early spring is a time when problems associated with accumulation of salts in pots of houseplants becomes evident. After a few months of indoor watering, as days lengthen and temperatures rise, damage begins to appear when plants begin new growth. If the soil has accumulated salt, it is wise to repot the plant in new potting soil. Replace much of the old potting soil at this time. After repotting, begin watering as described above.
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Watering trees and lawn
Q. When should I begin watering my trees and lawn? This has been a wet winter and I don't want to waste water.
A. This winter has indeed been wetter than usual for most of New Mexico. This has been the gift of El Nino. However, we are entering the months when precipitation usually declines and evaporation begins to increase. If the precipitation continues with good heavy snows or soaking rains, you can wait. It is more likely that we will have light rains which do not provide enough moisture to moisten the soil deeply, and as temperatures increase the water will evaporate from the soil much more quickly.
In addition, we are going into our windy season. The winds can quickly extract moisture from the soil. A shovel pushed into the soil can help you determine the status of the soil moisture. If the shovel enters the soil to its full depth easily and as you lift the shovel you notice moist soil at the end of the shovel, you can delay irrigation. Most perennials and trees utilize water to a depth of two-to-three feet in the soil. If our soils have received considerable moisture through the winter, the surface dries first. So, moisture in the top foot indicates that there is probably moisture below. This is not the case in the summer when the soil is dry to a considerable depth. Our irrigations or summer precipitation moistens from the surface downward, but may not moisten the soil to any great depth unless we take special care to provide enough water. In winter when there is subsoil moisture, as you notice that the soil begins drying to the depth of a shovel, begin irrigating at least once a month. In sandy soils, irrigate once every two weeks.
In most of New Mexico, we can water trees and perennials once every ten days to two weeks. Turf will need more frequent irrigation, depending on which type of turfgrass you are growing. Bluegrass and fescue can be watered every two-to-five days, depending on the water holding capacity of the soil. Bermudagrass, buffalo grass, and blue gramma can be watered much less.
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Watering trees through winter
Q. I planted Arizona cypress and Lanceleaf cottonwood trees last spring and have been watering deeply twice a week. How often should they be watered through the winter? Also, I am now (fall) planting another Lanceleaf cottonwood. What water regimen should be used?
A. The trees planted last spring should have developed a reasonable number of roots this summer and fall, so they may be watered once a month throughout the winter. If they are planted in sandy soil and there is a good layer of mulch over the roots, once a month will be sufficient. If the soil is clay, it will hold more water, but once a month should also be adequate. As you water now and in the winter, remember to irrigate the soil to the same depth as in the summer. When you reduce watering, reduce the frequency but not the quantity of water applied with each irrigation so the soil is moistened to the same depth.
Fall is a good time to plant trees, but the newly planted trees should initially be watered a little more often in sandy soil. Irrigate to the depth of the rootball once every two weeks until December, and then reduce irrigation to once a month until spring when the leaves begin to develop. Once leaves have developed, gradually increase irrigation frequency. (Remember to apply the same quantity of water with each irrigation.) By the time the temperatures begin to reach 80 degrees or more on a regular basis, you should be watering twice a month.
The reason you can water less often in the winter is because the water in the soil evaporates less rapidly during the winter, and the trees (especially the deciduous trees) use less water. An evergreen tree (your Arizona cypress) still has leaves and needs water, but even it uses less water in the winter. Mulch will help maintain more constant soil temperatures and soil moisture. It will greatly benefit your trees.
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Winter Irrigation 1-02
Q. How can I tell if I have enough rain or snow so that I don’t need to irrigate in the winter? I don’t want to waste water, but I don’t want my plants injured either.
A. The only way to know for sure is to probe the soil by digging or using a soil probe to determine the depth of moist soil. However, there are some general guidelines you can use.
Sandy soil moistens more deeply than silt or clay even with the same amount of moisture. Silt also moistens more deeply than clay. For example, one inch of rainfall (roughly 10 inches of snow) will moisten sandy soil to a depth of one foot, while moistening silt to six inches and clay to three inches. If the rain comes rapidly and runs off onto surrounding land or the street, then the soil will moisten less deeply. Snow may sit on the soil and slowly sublimate, or evaporate. In this case, you again have less soil moistened. In colder areas of our state, snow often sits on frozen soil, which cannot absorb moisture, so even more may be lost without benefiting the soil if the ground is frozen.
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Watering irises, how much 5-03
Q. I have noticed a lot of beautiful irises in several towns I visited in New Mexico. I thought they required a lot of water. Shouldn't people avoid such high-water plants in New Mexico landscapes?
A. There are some irises that need considerable water (Louisiana iris), but there are others that are extremely well adapted to New Mexico. The bearded iris, aril, and spuria irises do well here. They are adapted to the soil and their growing season is in the early spring when the weather is cool, so irrigation water isn't quickly lost to evaporation. The spuria irises are interesting because they don't need to be divided as often as others, grow taller, and are very elegant looking. The aril varieties are from very arid regions and especially well adapted to soils and moisture conditions in New Mexico.
As I speak to gardeners around the state, I continue to learn. I once complained to a Master Gardener that the problem with irises was that they only bloomed once a year. She has since shown me that there are bearded iris varieties that bloom two or more times a year. Irises are extremely beautiful, easy to grow and, if the proper types are chosen, very well adapted to New Mexico.
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Watering tree through the bark? 6-03
Q. I had a conversation with a nurseryman in Santa Fe yesterday. He promotes providing supplemental water to stressed trees by simply watering the exterior of the tree, particularly the bark. He says water can penetrate through the bark into the cambium, where the water will be distributed throughout the tree, providing additional internal water over and above that taken up by the roots. Could you please comment on this interesting concept?
A. Although it may be possible to get water into a tree in this manner, I think it would be very inefficient. There are a number of barriers to water uptake by plants in this manner.
The bark will absorb water, and only after the bark has moistened through to the phloem layer underneath will water be available to living cells for uptake. Most of the water absorbed by the bark will be returned to the air by evaporation and not available to the plant. Some plants, such as pinon, contain resins in the bark which will prevent water ever reaching the living cells below the bark, so almost all of that water will be lost to evaporation. Other trees with thin bark have waxy coatings on the bark. These coatings will cause the bark to shed rather than absorb water. In either case this seems like a very inefficient way to water trees.
Another factor to consider is that the layer of cells just inside the bark is the phloem layer which carries dissolved sugars and other material from the leaves to the roots. Thus, even if water is absorbed, it must go first to the roots. The roots are designed to absorb water, so it makes sense that the best way to get water to the plant is through the roots. Water from the roots must go through a special "active uptake" process which limits what minerals are absorbed with the water. This is for the good of the plant and also suggests that water uptake is best done by the roots that are designed for this.
I also checked with New Mexico State Forestry Division Urban Forester, George Duda. His comments included: "If that were true, various pathogens could enter the tree with water (rain), and perhaps we would not have trees at all. The purpose of bark is to keep things in and keep other things out of the tree (quoting Dr. Alex Shigo). That includes water. Watering with domestic water (ground water), directly on a plant, can introduce the various minerals in the water to the surface of the plant. It is not uncommon to see trees with the whitish cast on the bark, indicating mineral deposits. With our typically low humidity, there isn't much time for water to hang around long enough to do anything but evaporate."
In summary, I think it is most efficient to use the plant part designed for water absorption to provide water to the plant. This means that we must irrigate the trees properly (at and outside the dripline of the tree, not inside the dripline).
In times of water shortage, there are many people looking for more efficient ways to provide water to our plants. This is good, but we must be sure that what we are doing is right based on the anatomy and physiology of plants.
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Watering while away from home
Q. We will be visiting our children and grandchildren for the holidays and will be away for about two weeks. How can I be sure that my houseplants survive our absence? I have never had much luck asking someone to come to my home to care for the plants.
A. It is difficult to get someone to care for your plants like you do. For long periods of time, that is the only option, but there may be some loss of plants.
Another option is to minimize the needs of the plants while you are gone. The primary need in a two-week period is water. There are several things you can do to reduce the water needs or to extend the water supply during this time.
By lowering the temperature in your home while you are away, the plants will use less water. Most plants can tolerate temperatures as low as 50 to 55 degrees for this time. Lower temperatures reduce plant water use and will extend the time between irrigations. You can also remove plants from direct sunlight, placing them in locations that have bright light but not direct sunlight. Sheer curtains will help diffuse the light as well as provide increased security for your home. The plants need some light, but lower light coupled with lower temperatures will allow the plants to survive your travels.
There are ceramic slow watering devices to attach to plastic bottles filled with water. The ceramic portion is buried in the soil to slowly moisten the soil. (The plastic bottle should be upside down above the ceramic watering device.) This further extends the time the plant can survive your absence.
Rather than the slow watering device, you can also place the plants inside loosely closed plastic bags that will serve as greenhouses to reduce water loss. If the bags are tightly sealed, fungal problems may develop; however, a few holes punched in the bags will allow for air exchange and reduce the chance of fungus. Clear plastic bags should be kept away from direct sunlight. White plastic bags may be closer to the windows since they will reflect surplus light and not overheat.
While these techniques may not save every plant, they increase the chances for their survival without the need for a surrogate gardener during your absence. Have a safe trip.
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Soil moisture depth 8-03
Q. How can I tell how deeply my soil has been moistened when I irrigate? I want to keep my plants alive, but I don’t want to waste water.
A. An interesting characteristic of our soil is that it becomes quite hard when it is dry. This characteristic is well known to anyone who has tried to dig a garden in dry soil. Once the soil is moistened, it becomes much more workable and a shovel can penetrate it easily. This characteristic allows an easy method of determining the depth of dry soil. A metal rod (not necessarily pointed on the end) can be pushed into moist soil but will stop when it reaches dry soil, a pipe, rock, or a root. Such a probe may be a long screwdriver, a knitting needle, or a piece of rebar (concrete reinforcing bar) to which a handle has been welded. (Be careful to do this in a manner that does not let the bar impale you if the weld breaks.) Soil probes (for collecting soil samples) are available from some garden centers and mail order garden supply companies.
This characteristic of our soils is one of the differences between our soils and soils in many other parts of the country. In moist climates, the soil dries from the top downward and there is almost always some moisture at some depth. In the west, the soil is moistened from the top downward by precipitation or irrigation. Below the moist soil is dry soil (except near rivers and in arroyos). We cannot assume that there is moisture deep in the soil to care for trees and shrubs, so we must irrigate to moisten the root zone. The appropriate depth to irrigate depends on the plants but is typically 2 to 3 feet for trees and shrubs.
Soil that has been recently rototilled will be easily penetrated by the probe, even if dry. In loose soil conditions, you will need to feel the moisture of the soil at the end of the probe (or along the probe) to determine depth of moisture.
When using the soil probe, be careful not to puncture irrigation lines and other vulnerable pipes. Metal pipes, hard plastic, and clay tile pipes will not be as easily punctured, but soft plastic irrigation lines (polyethylene and similar types of plastic) are very easily punctured.
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Why water buffalograss seeds so much? 8-03
Q. I have planted buffalograss seeds. Why do I need to water several times a day? Isn’t buffalograss a drought tolerant grass?
A. Buffalograss is very well adapted to dry environments, but it needs water when the seeds are germinating. As the small seedling emerges from the seed, it is extremely dependent on water. After it has established itself and formed its crown (where the leave are formed and the bud is protected in the leaf bases), it can tolerate drought. Until that time, it will die if it dries.
If you plant buffalograss and natural rainfall maintains moisture in the top layers of soil in which the seeds are germinating, the grass does very well. This is the case when summer moisture is adequate (the monsoon provides moisture consistently). In dry summers such as we are experiencing this year, any buffalograss seeds that germinate in natural environments will probably dry and die. In our landscapes, if watering is permitted, we can establish buffalograss lawns. We must supplement the inadequate natural precipitation with frequent irrigation and/or mulch to keep the upper soil layers moist.
The mulch mentioned above is important. In nature, grasslands often have a mulch layer of old grass leaves. Grass seeds below the mulch layer may remain moist even if the monsoon doesn’t provide daily rain. Use of a thin straw mulch, or grass-clipping mulch, is helpful in establishing a lawn. As long as the mulch doesn’t shed water, creating a dry layer underneath, it reduces the required irrigation frequency and protects newly germinating seeds until the seedlings have emerged.
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