Twice a Week, Six to Twelve Hours: Why the Sprinkler Head Matters More Than the Clock
How often do you water an avocado tree? On our farm, the answer has been about twice a week, with each run lasting anywhere from six to twelve hours.
But the more useful answer is that the clock is not the main thing. What really decides how much water each tree gets is the sprinkler head on it.
Why is the sprinkler head so important?
Different sprinkler heads throw water different distances. The goal is for water to land under the entire canopy, so the whole root zone of the tree gets wet, not just a circle near the trunk. A small young tree needs a small spread. A big mature tree needs a head that reaches out toward the edge of its branches.
Because every tree is a different size, every tree needs a different amount of water. Matching the head to the tree is how you give each one the right amount, even when a whole row is on the same valve and runs for the same length of time. That is why, for us, how long we water is less important than what kind of head is on each tree.
Read nextHow to Check Soil Moisture With a Probe: Our Nine-Inch Test Under a Fuerte
Why the whole root zone needs to get wet
Avocado roots are not very good at drinking. Most of the feeder roots, 80 to 90 percent, sit in the top eight to ten inches of soil, and Avocado Production in California: A Cultural Handbook for Growers, Book Two, points out that they have very few root hairs, which makes water uptake relatively inefficient, so the trees need plentiful soil moisture across the root zone. A narrow wet circle by the trunk leaves most of the roots dry.
The opposite mistake is just as serious. In waterlogged soil, avocado roots begin to die from lack of oxygen after about 48 hours, even without disease, and soggy ground is where root rot gets its start. Spreading the water evenly under the canopy, rather than piling it in one spot, helps with both problems.
What about a young tree?
Newly planted trees are a special case. Their root ball is small and must never dry out, so the handbook suggests roughly 5 to 10 gallons a week split into two or three waterings, aimed at the root ball with a dripper by the trunk, a spitter pointed at the trunk, or a mini-sprinkler set to a narrow spray. It warns that young trees on a mature grove’s once-a-week schedule get alternately drowned and dried out — another reason the head on each tree matters.
The handbook’s irrigation chapter describes the same idea in grove terms. Fan sprays are often set to a 90° pattern aimed at the tree for one- and two-year-olds, switched to 180° at three to five years, and replaced with full-circle mini-sprinklers once trees are six or older. On a slope the head goes on the uphill side of the tree. Coverage changes the arithmetic, too: if a head wets only half the ground a tree occupies, it takes about two inches of water on that wetted area to deliver the equivalent of one inch across the tree’s whole space. Encouragingly, roots tend to grow where the water is, so an imperfect pattern matters less than it sounds.
If you are planning this for your own trees, our free Irrigation Zone Designer helps you work out trees per zone, pipe size and heads, and the Avocado Irrigation Calculator estimates how long to run them.
Why six to twelve hours?
The range reflects the trees. Sprinkler heads on avocado trees are generally low-flow, putting out water slowly so it soaks in rather than running off, which means longer run times than a lawn. Bigger trees with wider heads sit at the long end; smaller trees sit at the short end.
Twice a week is our pattern, not a universal rule. Heat, soil and the season all shift it, and so does wind, which dramatically increases a tree’s water use. For scale, the handbook estimates that a mature acre of avocados in most inland areas of Southern California needs at least 4,500 gallons a day in summer, even on drip, and more on hot, windy days. The handbook’s second volume puts July use for a mature tree on 20-by-20-foot spacing in Escondido at about 57 gallons a day, against about 20 in January — daily use, not a call to water every day. The general principles — and the mistakes that kill trees — are in our guide to how much water an avocado tree needs.
How much water goes into one avocado?
On average, somewhere from about 40 to about 80 gallons of water goes into producing a single avocado. It is a number that surprises people, and it is why we are careful with every drop. We break the math down further in how much water it really takes to grow an avocado.
Try this: Run your system and walk out to the edge of the canopy. If the ground at the drip line stays dry, the head is wrong, not the clock.
Every one of those gallons shows up in the fruit we ship. Our 4lb Hass box and 6lb Hass box ship free, picked the week they go out; between harvests, the waitlist on either page will tell you when fruit is back. Until the trees are picking again, the avocado scoop, the Hawaiian shirt and our hats ship year-round.
