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Balance irrigated, nonirrigated areas to conserve water

Q. Because we are an HOA, we are mandated to remove the grass surrounding our condos. We have over 100 mature trees. What is the best irrigation to put on these trees after the grass is removed? We want to save as many trees as possible. My particular unit had the grass removed many years ago and I have a large pine tree. It is irrigated with drip emitters surrounding the tree about 4 feet from the trunk. It is doing fine.

A. It is not only HOAs. Any entity that has property is required to conserve water by removing lawns. I would also include trees too large for the area and out of scale with the home.

Just substituting lower water-use plants and finding a lower water-use irrigation system alone does not work. You will lose some trees, particularly the large ones.

Do you want to choose where water is applied or have someone decide for you? Lowering total landscape water use requires finding a balance between open areas that need no irrigation with areas that require irrigation.

Your landscape committee should be charged with identifying zero water use areas. Filling these areas may include the use of statuary, murals, paintings, gazebos, etc. They don’t need water.

Start by identifying areas where loss of plants is not as important as other places. As these places eliminate the need for water, substitute statuaries, murals, paintings or gazebos that need no water but still beautify.

Next, shade the south and west sides of buildings to prevent overheating of these units during the summer. Use deciduous trees for solar heating during the winter.

Consider removing large plants on the north and east sides of buildings that have little function in heating or cooling the home. If plants remain or you find other plants, concentrate on smaller plants (less than 20 feet tall for single-story homes) that use less water. Water the remaining trees and shrubs in irrigation clusters for ease of water delivery and finding leaks.

Water savings come from the “averaging” of water use over the property and the creation of nonirrigated open spaces. You can have your cake and eat it too but not everywhere.

Q: In one of your previous articles you mentioned free wood chips. Where do you go to get them?

A: Call 702-257-5555 and get an update from the master gardeners regarding woodchip availability and what days and hours to get them. Woodchips are usually available in North Las Vegas about 100 yards east of North Decatur Boulevard and Horse Drive at the Center for Urban Water Conservation.

Organics in our desert soil are severely lacking unless plants are grown in them. That takes water. Most trees and lawns require at least 2 percent organics in the soil. Vegetables need more, usually closer to 8 percent for quality vegetables.

How to judge if your soil has organics in it? Use the color first. If your soil is very low in organics it will be closer to light brown or even tan in color. If organics are present, desert soils become darker and start develop some structure.

The higher the organic content in the soil, the darker its color. If soil has 2 percent organics in it, it has a color similar to coffee with a creamer in it. If it has 8 percent organics, it is chocolate brown in color.

Visually is how to judge if organics should be applied to Mojave Desert soils or not. In most Mojave Desert soils, we judge a soil’s organic content from its darker color. That’s because it starts off light tan in color.

If your soil has a darker color, then adding organics such as woodchips won’t help much when planting trees and shrubs. But that organic content may not be suitable for growing quality vegetables without compost added.

Q: My friend is asking if he should remove his lemon tree? It’s in a small planter and close to the outside wall of his house.

A: When trees are small and just starting to grow it is fairly easy to encourage the roots to grow away from the wall with irrigation. Move the applied water to the side away from the wall. Try that first and see if it helps.

The roots will follow the water and grow in that direction. It is best to keep the area close to the wall as dry as possible so the roots will not grow in that direction.

It also reduces the chance that the combination of water and soil will “eat up” the foundation, particularly if you are using Las Vegas tap water which has a lot of salt in it.

I usually tell people to try and keep the area close to the foundation free from applications of water by about 3 feet. Water spreads horizontally depending on the soil texture (percentages of sand, silt and clay) but applying water no closer than 3 feet from the foundation keeps most soils close to the house dry.

A spread of about 10 inches in all directions from the point of application is the bare minimum for soils that contain a high percentage of sand. Most plants are usually planted a distance of approximately half their mature height anyway to minimize branch interference growing into the house.

Q: I have a few Aleppo pine trees growing in Logandale that I fertilize and water regularly. I am wondering how much fertilizer to give them each year and how much to water them. I am wondering if I can water them less often due to a shallow water table here and also apply less fertilizer.

A: Trees vary in the amount of fertilizer needed. It is not one size fits all.

In my experience, trees like Aleppo pine need a small amount of fertilizer applied in the spring and early summer when they are growing. They will not need as much as an orchard tree.

They require more fertilizer applied, particularly if the area around them is kept clean. Landscape maintenance companies do a great job keeping areas clean by blowing (mostly) plant debris into community streets.

If plants grow and take away nutrients from the soil, then you must give the soil something so it can break it down and keep plants healthy and vibrant.

Let ornamental trees like Aleppo pine tell you they need fertilizer. They tell you by the color of their needles and the density of their crown.

That’s why I like compost (or aged manure) as a fertilizer. Compost slowly releases its nutrients and rebuilds the soil when lacking.

Fertilize ornamental trees like Aleppo pine before they need nutrients. Stay slightly ahead of the curve. No need to overfertilize. It wastes money, labor and time.

After a few years of experimenting, you will find the right rhythm for applying fertilizer to your pine tree. Adjust it for size.

When using compost, mostly nitrogen and potassium is needed because we don’t need pine trees to flower or fruit. Fruit trees need a different kind of fertilizer because our expectations are an abundance of fruit.

A pine tree that size should put on about 8 inches of new growth every year to keep it full. Because pine trees are all green”and no flowers or fruit, you can apply less of the middle number (the amount of phosphorus).

A single application of compost once a year is enough for all fruit trees. For example, most fruit trees do just fine with one full fertilizer application higher in phosphorus or splitting this application into twice a year.

As trees get bigger, they use more water. That is just common sense. Big trees use more water than little trees. You can’t wean a tree into using less water. It needs water and more water as it gets bigger.

If your water table is 5 to 7 feet deep you will need to get its roots into that water table. You do that by stretching the watering it gets so it takes longer and longer for the roots to get it.

When you irrigate, water the trees deep when you do, water them less often and watch the tops for damage by the sun. Force the tree roots to go after deeper water and see how many fewer irrigations they need to still maintain growth and canopy.

Most pine trees have taproots or large roots that can grow deep if given the chance. You might need to water occasionally during the summer months to get those roots to take.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.

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