I’ve always wished there were a simple formula that could tell us how much and how often to water an avocado tree. Alas, the variables are too numerous and complex: weather is ever-changing, different soils have different capacities, each method of watering creates distinct conditions, etc.
Yet I bulled forward and made this table anyway, showing approximately how much and how often to water avocado trees of different sizes in each month of the year in Southern California.
Even though such a table cannot be perfectly accurate, it’s pleasantly usable. Even if you follow the table blindly without making any adjustments, your tree is likely to do well.
If you are interested in being a little more efficient and effective, you can tailor the application of the numbers by keeping in mind a handful of things about how I made it and how avocado trees use water.
Important note: Be sure you’ve planted your avocado tree properly and watered it through its first couple months properly before starting to use this table.
Gallons are for the valleys
How did I come up with these numbers of gallons? I used weather information that is similar to where most people in Southern California live — basically, the valleys: roughly five to fifteen miles away from the beach. (Specifically, it’s Zone 6 on this map.) Anaheim in Orange County is an example of a city in this zone. If you live closer to the ocean, well, aren’t you cool and comfortable? And so is your avocado tree. You can give it 10% less water in the summer. Likewise, if you’re more than fifteen miles from the ocean, your avocado tree feels the heat and might enjoy 10% more gallons than the table shows for the summer months.
But these numbers aren’t just theoretical. They are also based on the quantity of water that I have found to work well on my avocado trees.
In my experience, you can’t give avocado trees much less without them suffering. (I’ve tried.) And it’s unnecessary to give them much more. (You won’t get more fruit, which is the point.)
Frequencies are for sprinkling and mulch
The table makes a couple of assumptions. One is that you are sprinkling or spraying the water under the tree, not using drip emitters. If you are using drip emitters, then the gallons don’t change but the frequency does. You must water more often with drip, every two or three days in summer, for example.
Another assumption is that there is mulch under your avocado tree. Leaves or wood chips under an avocado tree are extremely beneficial in myriad ways, one of which is allowing the tree to go longer between waterings. If you don’t have mulch under your tree, you really ought to add some.
What did I base the table’s frequencies on? If you’re familiar with the concept of evapotranspiration (ET), then you might be interested in knowing that the table says to water after about one inch of ET has occurred. If you’re not familiar with ET, then forget that. Just know that the table’s frequencies are what I’ve found avocados to prefer.
If avocados are routinely watered too often, they become susceptible to root rot disease, among other problems. If avocados are watered too infrequently, they stress and their leaves brown and they might even drop fruit. My table’s frequencies are the safe and happy medium.
That being said, remember that the frequencies are meant as a point of reference, and you may find that the soil in your yard needs slightly more or less frequent watering. How to determine this? The surest way is . . . as I describe here: “Get your hands dirty: Discover the truth about your irrigation practices.”
Also, be sure to increase the frequency during severe heat waves. When the extreme heat of July 6 and 7, 2018 hit Southern California, you needed to water every day. I saw the avocado trees in the area that didn’t get that custom care; they suffered. (Here is my strategy for watering when extreme heat hits: “How to water plants through a heat wave.”)
No automatic watering in winter
Where avocados grow wild, winters are even drier than ours in Southern California. So once our rains begin, sometimes in November but more reliably in December (December 2017 notwithstanding!), you should stop watering your avocado tree automatically. (That’s why the table shows the frequencies for those months in parentheses.)
Unnecessary irrigation in the winter not only wastes water but more importantly can keep the soil soggy and disease prone. After we’ve had our first couple inches of winter rain until around the end of March, only water an avocado tree if there is a dry spell of at least a couple weeks.
And when you do water, give the tree approximately the amount it has used in that interval according to the table. For example, for a 10-foot tree in February that has received no rain for two weeks, give it about 55 gallons. (That number comes from 110 gallons for the month divided by 28 days, times 14 days.)
Big trees get water elsewhere
The table only goes up to 14 feet mostly because bigger trees in a normal yard will have grown extensive root systems that drink from neighboring plants, maybe even from your neighbor’s plants. So if you have a big avocado tree, you almost surely can give it less water than an avocado farmer would have to give such a tree in an orchard.
It’s impossible to say how much to give your big tree. Just think about what is being watered under its canopy and even within ten feet or so of the outer edge of its canopy. If there are irrigated plants all over that area, then you might not need to give the tree any water of its own. This is particularly true if there is lawn being watered within the tree’s reach.
Using the table: a small tree
Here’s an example of how I can use the table to water one of my trees. I have a Gwen avocado tree that has a canopy diameter of about three feet.
Here in June, the table says that such a tree needs to be given about one gallon per day. I get this number by dividing 28 gallons by 30 days. And I’m supposed to water it every five days. This would mean giving it about five gallons every five days.
I water this Gwen avocado tree with a micro-sprinkler. I measured how much water the micro-sprinkler puts out by turning it on, sticking it into a bucket, and timing it. I found that the water in the bucket filled to one gallon after ten minutes. That’s the equivalent of six gallons per hour. If I want to give the tree its five gallons, then I should run the sprinkler for just under an hour.
What I’ll do in reality is round up. I’ll water for an hour every five days in June. One reason for this is that the sprinkler is set to spray a little beyond where the tree’s roots are. (I know this because I’ve poked around down there.) So I’m potentially wasting some water, but it’s worth it because I want the tree to be able to expand its root system as rapidly as possible, giving it fortitude during temperatures over 90. This happens with some frequency in summer because my yard is twenty miles from the ocean. (I’m in ET zone 9 on the map referenced above, which you can see in more detail for San Diego County here). For this reason I also need to add about 10% to the gallons in the table.
Young trees like this Gwen can grow fast: beware. By September, its canopy might be four or even five feet wide, meaning it will need more water to fuel those extra leaves. It will have rapidly graduated out of the “3 feet” column.
Using the table: a big tree
One more example, this time with a bigger tree. I have a Hass avocado tree, and I measured its canopy to be 14.5 feet in average diameter. The summer of 2018 will be its sixth summer in the ground in my yard.
Here in June, the table says a 14-foot tree needs to be given about 20 gallons per day. I get this number by dividing 611 gallons by 30 days. And I’m supposed to water it every five days. This would mean giving it 100 gallons every five days.
I also water this Hass avocado tree with a micro-sprinkler, and I have measured that this sprinkler applies about 25 gallons per hour. So to give the tree 100 gallons, I must run the sprinkler for four hours. I’ll add a little extra to that because the tree’s already a tad over 14 feet and because of my hotter location.
Click this link to download the table as a PDF: “Watering avocado trees in California: how much and how often.”
How can I help you apply the numbers in the table to your tree in your situation? Let’s grow some guacamole!
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