The mature size of trees, shrubs, and other plants, their numbers, and their origins determine the amount of water needed to support your landscape. Once landscaping is complete, the amount of water required is determined. You will not be able to change the amount you need many times over without removing or changing plants.
Massive trees like Aleppo pines, poplars, poplars, and lacebark elms require deep irrigation and more water. For large trees, water should be applied to moisten the soil 3 feet deep or more. Medium-sized trees like chitalpa, ash, and African sumac should be watered 24 inches deep. Small trees like Desert Willow, Texas Mountain Laurel, and California Redbud should be watered 18 inches deep.
Their root depth affects their health and resistance to heat damage. The same applies to bushes of similar size.
As the number of plants used in the landscape increases, more water is required. Perhaps not at the beginning when they are small, but when they get bigger.
Also, the amount of water they need isn’t necessarily additive as planting close together can affect each other’s water usage. In other words, two ash trees planted close together affect sunlight, wind, watering, and other things that affect their individual water use.
The type of trees – whether mesic or xerian – also influences how they react to applied water. Mesic trees and plants come from humid climates (think oleanders, palms, irises). These plants do not do that well when water is scarce. They can’t grow and scroll as quickly after a drought as xerian trees and shrubs (think acacias, Texas mountain laurel, penstemon). Xeric plants have coping mechanisms that deal with water shortages (like shedding leaves or slowing growth).
Xeric plants can be made to use less water and then react quickly with vigorous growth and increased density when water is available. Many xeric plants are sensitive to heavy daily watering, especially at high temperatures.
However, Xeric plants are the best ways to save water. Most of the water savings in xeric plants are achieved through less frequent watering rather than the amount of water used.
You can have the best irrigation system and plants in the world, but if you use the water incorrectly, you will still be wasting water.
Q: We have a one zone (valve) irrigation system in our garden with around 50 different plants. The plants include two old olive trees, citrus fruits, a dozen roses, flower pots, and various bushes and cacti. We water the cacti by hand. We automatically pour deep once a day for about 20 minutes. Some friends of ours water three times a day and my son water twice a day with no problem. Please comment.
A: The flower pot plants determine how often a single valve irrigation system is turned on – its frequency. The plants in the flower pots control when water is turned on or they suffer and we see it. The remaining plants adapt to the daily watering schedule.
You are happy with this watering schedule. Everything looks good. How about your plants in the long run?
Irrigation in the desert is the lifeblood of a landscape. Plant roots grow best where there is the ideal mixture of water and air. There has to be a balance between the two, but not too much of either, for the plant to be healthy and to survive.
Water too often or drain poorly and the roots will drown. If the plants skip a hot day, they will suffer from drought.
Daily watering promotes the growth of the plant roots near the ground. This is where this ideal mix happens. Daily watering can be fine for small plants with shallow roots, but not for deeply rooted trees like olives or citrus fruits.
The larger plants prefer lots of water at once – slowly or in a reservoir around the tree – and then no more water until half of that water is used up. This irrigation strategy promotes deeper rooting of the trees, greater tolerance to hot weather and better resistance to strong winds.
Ideal for the plants, therefore, more irrigation valves are required to encourage deeper rooting of trees and shrubs. However, if you are happy with the appearance of the plants, happy with your water bill, just want to use one valve, and don’t worry about the health and longevity of the trees, watering once, twice, or three times will work.
If you haven’t, cover the soil with a layer of wood chip mulch to control weeds and save water. When wood chips rot, the roots of large trees have more area to find places to grow. The olive trees can handle stone mulch, but wood shavings for citrus fruits and roses work best in the long term.
Q: Ten bottle trees that were planted last year thrived, but then suddenly lost all the leaves at the top in the wind. The trees are watered with drops twice a day and three times a week for the past month. The rest of the trees and leaves look healthy. My landscaper suggested that the wind wipe the leaves off. I have doubts that my neighbors’ bottle trees of the same age look perfectly healthy.
A: I like to follow the KISS principles and get those possibilities out of the way before coming to unusual conclusions like high winds. I suspect this problem is related to their watering, and not necessarily to the wind.
Trees lose their leaves at the top either from lack of water or from too much water. Both cause the leaves to detach from the branches and the wind to simply blow them away. BTW, a quick google tells me that bottle trees get 60 feet tall with watering – big trees as they get older.
Watering applied two or three times a week in late April and early May is about right for established trees, provided they are given adequately and applied to a large area under the canopy. This means that the amount of water should be measured in gallons rather than minutes. The number of emitters and their spacing are important pieces of information to be shared with me as they are responsible for the amount they apply and the distribution of water under the canopy.
Trees planted from 15 gallon containers should receive at least 8 to 10 gallons of water when first watered and probably twice as much as in the second or third year when the roots explore the surrounding soil and the tree becomes larger and more established . Two or three drip heads 12 inches from the trunk are all that is required for the first year after planting.
But in the second or third year after planting, the trees need more drip jets that are farther from the trunk. If you double the number of transmitters and place them further away from the trunk, this is achieved without changing the number of minutes.
Using a thin piece of 4-foot rebar, make sure the water is applied deep enough by pushing it into the ground in several places immediately after watering. The soil around bottle trees should be wet to a depth of 24 inches immediately after watering at a young age and 36 inches as they grow larger.
Q: What can I use a privacy screen that is less than 3 meters high?
A: Texas Ranger Green Cloud or Gray Cloud varieties, also known as Texas Sage, grow to this altitude by watering, retaining their leaves (if it’s a warm winter), and becoming denser when pruned by hedges. Plant them 3 to 4 feet apart if you are growing them for privacy, mix compost into their backfill as you plant, and water the heck out for the first few days.
Texas Ranger is from the Chihuahuan Desert in the United States and Mexico. Once established, it doesn’t need frequent waterings unless you want it to grow quickly. However, it does require deep watering if the roots are to grow deep and become more tolerant of hot weather and drought.
These medium-sized shrubs process either stone or wood chip mulch. Fertilize them lightly in the spring with a second application of high nitrogen fertilizer – think ammonium sulfate, 21-0-0 – mid to late November. If you water over the winter, they will remain evergreen in the coldest winter.
Bob Morris is a horticultural expert and Professor Emeritus at the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to [email protected]