Xtremehorticulture

Xtremehorticulture of the Desert

Saving Water Through Landscape Design

Leave a Comment / conserving water, growth, mesic, shade, xeric /

           Designing a landscape for only energy conservation (an example is lowering the cost of running the air conditioner) is quite simple. All you must do is ask yourself, “Which sides of the home are the hottest?” Create shade on the walls and windows close to the house for these hot sides. Try not using plants when you do this. Use them if you must. Creating shade that doesn’t use water requires more “brainwork” but may be necessary in the desert. Usually, the hottest areas are the exposed South and West walls and windows of a home. If you don’t know which sides are hot, use a “temperature gun” (infrared laser for measuring temperature) during the hottest times of the day. You can buy an inexpensive but accurate gun for less than $25. The hottest areas are typically handled by shading the walls and windows on these hot sides rather than shading the roof. Roofs are usually better insulated than the walls and, in particular, windows. Selecting plants to save summer electrical cost is quite simple since shading the south and west walls and windows is most important. Select plants that are “winter deciduous” so that the sun warms the house during the winter months. If water is plentiful, how much water these plants use is not important. To lower electrical costs, regardless of water, always shade the hot walls and windows of a home. Irrigation design is important. I can’t stress the importance of using “hydrozones”. Hydrozoning is when the valves control when to water plants. Xeric (desert) versus mesic (nondesert) plant water use relies on how frequently each are watered. Use mesic plants when water is provided to them at the same time. How deep plants are watered is adjustable by adding or subtracting drips. How frequently they are watered is not.  Xeric plants are not watered as often as mesic plants if you want to conserve water. This means plants are matched to a specific irrigation valve; xeric plants are put on one valve and mesic plants are put on a separate valve. This means you must know the difference between xeric (desert) and mesic (nondesert) plants. Xeric or desert plants will grow more rapidly than mesic, or non-desert plants, if they are watered like mesic plants. That’s just they way they are. Xeric plants are more “adjustable” in their growth if they are all watered at the same time, and you can adjust the frequency of watering. When mesic and xeric plants are placed on the same valve, mesic plants will signal you to water and not the other way around. When water is scarce, xeric plants (desert plants) tolerate dry soil better than mesic plants. They have capabilities of saving water through many different traits including leaf drop, changes in leaf and plant size, as well as changes to the plant at the genetic/molecular level. Xeric plants handle water shortages more efficiently than mesic plants. Being from the desert, xeric plants have evolved to soil drought. Water xeric plants less often. This means watering them with a separate irrigation valve (hydrozones). Because of this, xeric plants can get by (and often benefit) when watered less frequently than mesic plants. For instance, foothills (not Blue or ‘Desert Museum’) palo verde (Parkinsonia microphylla or Cercidium microphyllum, depending on the source of its scientific name) is a true xeric, desert, or low water use plant. It grows in flat, dry areas throughout the Sonoran Desert of the American southwest. It can survive in dry soil for long periods of time. They can’t survive without any water, but they will require watering, deeply, less often. When water is limited, xeric plant growth first begins to slow or stop. That can be hard to see. Controlling their size, controls their water use. If dry soils continue, xeric plants start dropping their leaves. That is easier to see. Fewer leaves mean there are fewer leaves present to lose water. The canopy begins “thinning out.” It’s time to water! If the soil continues to remain dry, then remaining leaves begin scorching and branches begin dying. Plants are starting to look bad. In the case of cacti, their stems may begin to shrivel. You don’t want limb dieback, or cactus shriveling, in a landscape. That’s not pretty. On the flipside, they may not look the best when that dry spell is over, but at least they have survived! In a landscape, deeply watering these plants once every 4 to 8 weeks is usually enough. Observing xeric plants regularly (once a week in the summer) will tell you if it’s time to water or hold off. Branch dieback in palo verde and other trees (mostly mesic) can be confused with the palo verde root borer. Occasionally a single, isolated branch will begin dying back to the trunk during the summer if these insects have been feeding on the roots. In cases like these, a systemic insecticide for borers might be the only solution available. As with other plants, apply this insecticide only after flowering to avoid the risk of hurting pollinators like honeybees. How much water is applied is controlled by the size of the emitters (two-, three-, four-, or 5-gallon drip emitters) or a moat surrounding trees and shrubs. For 10- to 12-foot-tall trees, flat moats about 6 feet in diameter, and 2 to 3 inches tall, will work. Figure that in most level soils, 1 inch of water will wet roots about 15 to 18 inches deep. My experience tells me that at least half the area under the tree’s canopy should receive this water. Once the roots of a tree are watered deeply enough, the only changes that need to be made to an irrigation timer are seasonal. If you try grow deep-rooted, xeric (desert) trees in a fescue lawn (called a mixed landscape which I don’t recommend), the tree frequently dies, or “wiggles” in the soil. This is because it is watered every day the

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Mastic Tree Problems

Leave a Comment / growth, leaf change, mastic, newly planted, pistache, Pistachio /

Q. Can you tell from the attached pictures what might be happening to our mastic tree? Mastic tree. A. My guess is that the new growth is filling a “hole” made when the plant became a shrub. Mastic is a Mediterranean tree or shrub that grows slowly and naturally as a bush, to about 20 tall by 20 feet width. It requires, at the least, annual pruning when it is young to shape it into a single or multitrunked tree. It is best used as a background tree or shrub and not a smaller version of the larger Chinese pistache. It is not as pretty. It lacks fall color, tends to be shrubby, and smaller, but does have red ornamental nuts when they are young and before they ripen around August.             If this plant were mine and I wanted a small tree instead of being shrubby, as it tends to be, I would start to prune it in the winter or late fall months. Make a decision whether you want it as a single or multi trunk tree and make the appropriate cuts.  I would expose the trunk or trunks of this tree up to my knees by starting at the bottom of the tree. I would eliminate any growth below my knees and keep any upright growth. If I saw any suckers at the base, I would eliminate them. While it’s young, I would eliminate any growth growing downward or horizontal. I would concentrate most of my pruning efforts on keeping any upright growth to make it look like a tree and give it some height.             Water it like you would an olive tree. It is mesic in its water use. It will attract the leaf footed plant bug. Shearing this tree with hedge trimmer is a mistake. Fertilize this tree once or maybe twice lightly with a standard landscape fertilizer such as 16-16-16.

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Plants Grow Toward Light

Leave a Comment / growth, Light, plants /

Q. I pulled out my old, bent crepe myrtle and bought a new one from a grower. It’s still small, but I noticed the “trunk” is already curving. Is this going to be a problem like the old one? Is there something I should do now, or will it straighten itself out as it grows? When I plant it, should I put the root ball in the ground at an angle so the trunk is pointing more or less straight up? Pine tree leaning due to shade on its West side from the eucalyptus. A. As soon as you plant it, the new growth will start straightening (bending toward the light) as it grows. The light will come at it from all different directions than in the nursery. When you plant it, plant it as straight as possible and let the plant figure it what is straight with its new growth. You can help it “straighten out” with pruning. As you guessed, the plant will figure it out as it grows. Pine tree leaning. What is not known to you is that there was a large tree that burned down (died) last year to the left side of that tree on the other side of the wall. That’s why it is leaning. Leaves and buds are light receptors. The side that is open will “fill in” with new growth as long as the plant gets enough light, water and fertilizer to push this new growth. The top growth from leaves and buds (where it “sees” light which determine where and how stems develop) is what we call “positively geotropic” which means it “grows up”. Roots are “negatively geotropic” which is a fancy way of saying roots “grow down”. Of course, root growth is encouraged by water, air, and fertilizer. Top growth is encouraged mostly by light but heavily influenced by irrigating and applying fertilizer to push new growth.

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Both Nitrogen and Iron Fertilizers Contribute to Dark Green Plant Color

Leave a Comment / green color, growth, iron chelates, iron fertilizer, nitrogen fertilizer /

Q. Thanks to your previous advice I used an iron chelate, applied it to the soil in March, and got my plants to develop a dark green color rather than a yellowish green color. Shrubs that the reader was speaking about. Not sure but they do look like desert natives. A. There are many things that develop a yellowish color in plants besides needing an iron fertilizer or chelate. The plant you questioned appears to be native desert plant, a Texas sage. That is odd needing an iron fertilizer for native desert plants. They are usually accustomed to our soils and don’t need iron. Watering or a nitrogen fertilizer may be the issue. Not sure but I do recommend iron chelates that contain EDDHA as the chelating agent. It works in all the different alkalinities of desert soils. EDTA and DTPA iron chelates don’t. Regardless, the two fertilizers that can create dark green leaves are nitrogen and iron. If that plant is native to the Western US, then yellowing leaves is more likely issues involving either nitrogen or watering too often. Nitrogen causes stem growth as well as dark green leaf color. Adding only an iron fertilizer or chelate causes the new growth to become green but does not stimulate new growth that much. When iron is involved, the yellowing occurs on newer growth. Yellowing due to a need for nitrogen occurs all over the plant. Also, the yellowing of leaves due to iron may be a yellow leaf color while the veins of the leaves stay a darker green. wk Winter yellowing I call bronzing of a shrub due to very cold temperatures for Las Vegas. Two types of “overwatering” can occur; watering too often or giving the plant too much water all at once. It is easier for the plant to resist “overwatering” from the second kind than the first kind. It is easy to water desert native plants too often when placed on the same irrigation line as non-desert plants. Mesquite leaf yellowing and leaf drop during winter cold temperatures. Another reason for yellowing of plant leaves are cold temperatures. This type of yellowing is more of a “bronzish yellow” leaf color and happens during cold weather. Cold weather damage to mesquite leaves (yellowing or bronzing) is a common occurrence during cold weather just before the leaves may fall from the tree if it gets cold enough.

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Apricot Poor Leaf Color Could be Fertilizer or…..

Leave a Comment / fertilizer, growth, iron, leaf color, nutrients /

 Q. I have an apricot tree and the leaves are a lighter green during the past couple of months. Are the leaves lacking nutrients? Apricot leaves should be dark green when it is growing and in the summer. This color is a problem or late in the fall or winter just before leaf drop. Correct yellowing apricot leaves with an iron chelate applied in the spring or compost applied to the soil surface or both. A. Perhaps. Look at this year’s growth in several places as well as its leaf color. New growth should average about 18 inches for productive trees. Leaf color should be dark green. If leaf color is a light green and new growth is well under 18 inches, then consider applying a fertilizer or rich compost. Not all new growth of apricot is red. Some stays green. This is excessive new growth on a mature apricot and should be cut back. Prune it back with a hand pruner anytime you see it. You don’t have to wait until winter or leaf drop. Look at Growth and Leaf Color  Fruit tree fertilizer is applied in the early spring, usually once a year. Unless the soil is very, very, sandy, once a year application of a fruit tree fertilizer is usually often enough. Use the rate on the fertilizer bag as the maximum rate to apply. If applying twice a year, divide the rate on the bag in half. Apricots when young should get an average growth of 18 inches in a year. When it is mature maybe 8 to 12 inches of new growth each year. Apricot leaves showing inter veinal necrosis…or leaf yellowing. Defintely needs some iron chelate applied in early spring. But what about the leaf cupping? Weed killers can cause the leaves to cup. So can excessive heat in the summer. Soil Improvement Soil improvement may be needed also. Use rich compost instead of a fertilizer. Never apply a fertilizer or rich compost closer than 12 to 18 inches from the trunk. Both fertilizers and rich compost can damage plants if applied too close. To be on the safe side, water the soil immediately after the application of a fertilizer. Water “dilutes” fertilizer and rich compost. Never apply compost or fertilizer near the trunk or main stem of a plant. When applying a rich compost, rake rock or bark mulch away three feet from the trunk in all directions. Apply a thin layer (1/4 inch) of rich compost, water it in and rerake the surface mulch back into place. Do this once every year. If it is a nutrient issue from a lack of fertilizer, you will see a change in the leaf color in about two weeks. This color change will last months. Apricot tree near a lawn but the roots can choose where to grow. Growth might not be enough. Check fruit production last year, fertilizer applications and soil improvement. Inspect Irrigation Light green leaves can also be from either drought or watering daily. First correct daily irrigations during the summer. That’s a big no-no except for lawns, flower beds and areas for growing vegetables. Big trees and shrubs can’t handle that. When watering, apply water deeply to tall plants. If it calls for more continuous watering, increase the size of the irrigated area under the tree. Apply water to at least half the area under a plant. If the leaf color is light green, it may be a sign the tree is watered too often. Give the roots at least one day between irrigations during the summer otherwise the roots may “drown”. This gives the soil a chance to drain water and the roots to “breathe.”

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Mesquite Bushes Can Be Trained to a Tree

Leave a Comment / form, growth, honey mesquite, irrigation, management, pruning, riparian, training, watering /

Q. I grew up in a part of Texas where mesquites were bushes not trees.  We have a small backyard here in Vegas with two mesquite trees in it; one large one and one slender one. There is little or no green on them, just wood. There are so many woody branches I am wondering if they will ever give us shade.  Would you please educate me on this? Native honey mesquite growing in the Mojave Desert just outside of Las Vegas, NV A. The Texas mesquite or honey mesquite is a shrub that we prune into a tree form. The plant grows well here but is usually not a preferred type of mesquite because of its long thorns. There are improved types of mesquites that are usually preferred.             With a little bit of care when they are young they can be trained into a tree form.             In our climate many mesquites drop their leaves in winter and so are considered deciduous to semi evergreen due to winter cold. In warmer climates they tend to stay evergreen during the winter unless there is a cold spell.  One of the ornamental mesquites in the nursery trade, claimed to be thornless, showing dense canopy and shade, a sign of abundant water.             We consider our local mesquite to be a riparian species of plant. In other words it puts on growth when water is available and slows down when water is not. When mesquite trees are watered frequently they can put on large amounts of spindly growth, perhaps 8 feet or more each year.             Mesquite are normally very deep rooted plants in the wild. Being deep-rooted gives them the capability of avoiding long periods of time without water. For this reason they can be very drought tolerant if they have rooted deeply. Native mesquite growing in the Sonoran Desert near Jerez, Mex, demonstrating sinker roots tapping into deep water from a nearby river.              If mesquite trees are watered too often, their roots will tend to be shallow and not deep-rooted, a frequent problem in over-irrigated landscapes. They also tend to put on a lot of wood because of frequent irrigations.             Mesquite trees handle pruning very well and their growth is very adaptable to landscape management. They do well with light fertilizer applications annually. They should be grouped with other desert plants for irrigation purposes.             After training these plants into a tree form they do not require a lot of pruning. In fact heavy pruning just encourages a lot of new growth. I would remove lower branches just high enough to allow traffic to pass under them.             Frequent irrigations will cause these plants to be lush and provide dense shade. Watering less often will cause them to become more open and provide lighter shade. Remove branches that are crossing or growing too close together.             Limbs would be removed at their point of origin, not by hedging or simply cutting them back.

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