The Q&A Archives: Water Needs Of Eucalyptus Trees in the Desert

Question: We planted two year-old trees about 14 months ago. Both are eucalyptus--a grey-ghost, and a silver dollar. In this 110 degree heat, I want to give them adequate water, so late at night, I spray them down. My neighbors tell me that I should not give them that much water even in this Las Vegas desert heat. I check the ground down about 4 inches, and it is dry when I water them every other evening. The water needs of these trees are very different (I am told). I need some expert advice. I don't think I am getting the advice I need from the books that I have. Please help.

Answer: Eucalyptus accept extremely arid conditions and usually don't require extra watering after about one or two years. If the soil is dry 4 inches deep after you water, you are watering ineffectively. Here is some information that should help: Desert soil and water both contain salts, which can accumulate in the root zone over time. This salt buildup forms where the water stops penetrating. If you ?sprinkle? plants lightly and frequently, salts will build up in the top layers of soil and damage or kill your plant. Deep watering?or leaching?prevents this by flushing the salts past the root zone.

Roots also need oxygen to survive and soil that is continually wet doesn?t provide it. Use a soil probe (any long, pointed piece of metal or wood to poke into the soil) to check how far water has penetrated. The probe moves easily through moist soil, but stops when it hits hard dry soil. For trees, water should reach about 2-3 feet deep. There are numerous variables involved for watering schedules, such as type of soil, how fast or slow it drains, sun and wind exposure at your site, temperature, age and condition of the plants and much more. Use the information above to determine how moist the soil is before automatically applying more water. The following frequencies are guidelines only for the summer months when temperatures are high (100+) and winds are drying.

desert adapted trees, 1st year, once a week
Established trees, every 7-21 days

In cooler months, water about once a month after the trees are established.

As a tree grows, its new roots tips, where nutrients are being absorbed, spread out laterally. If you are watering only within a few-foot area at the base of the tree, it's not really being watered effectively. Expand your watering zone out PAST the tree's canopy. As the tree grows, continue expanding that water zone. If you have an irrigation system, you need to move the emitters out. If you use a hose, just drag it out further. In any case, water slowly and deeply to ensure water penetration and to leach salts below the root zone. For newly planted trees, water should reach about 2 feet deep, expanding to 3 feet as it matures.

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