In June of 2023, I planted a GEM avocado tree. It was a good-looking tree, on top and bottom. The leaves showed healthy new growth and the roots were abundant and with new white tips. I planted in the best way I knew, a way in which I’d planted many trees before that grew into productive mature trees. Here it was on planting day:
All looked perfect through that first summer. And at the end of the first year, 2023, the GEM was as big and healthy as I could hope. I patted myself on the back for having taken good care of it. Here it was at the beginning of its second year.
But when the GEM began to flower in spring, some leaves started to show brown edges.
The tree continued to grow, however, and while its new leaves were a bit smaller than they should have been, they were fully green.
Until it really warmed up.
On June 22, the temperature reached 103. On July 5, the temperature reached 101. It was over 100 again the following week. The GEM avocado tree’s leaves began to brown.
I thought I had been watering enough. I added a cover of shade cloth to give the tree relief, and I watered even more. But the leaves did not stop drying up.
The GEM’s deteriorating health continued until the whole tree was crispy and dead by the end of summer.
Why?
What killed my GEM?
Was it the heat of summer? Probably not. I’ve got dozens of other avocado trees in my yard that did fine through the same heat. Moreover, in the GEM tree’s first summer it coped with heat that lasted longer and reached higher temperatures.
Was it a bad rootstock? Doubt it. The tree was on a clonal rootstock called Leola. And though I don’t have more trees on that rootstock to compare to, I had planted two other trees on two different rootstocks on the same day in the same area in June of 2023, and their lives had a similar trajectory. They grew well the first year, and then declined in the second.
For example, I planted this Maluma avocado tree that was on a clonal Dusa rootstock right by the GEM:
The Maluma on a different rootstock also declined in its second summer until it was dead soon after the GEM died.
Incidentally, I’ve got older avocado trees on Dusa rootstocks elsewhere in my yard that are growing well.
Was it a disease in the dirt? I don’t think so.
I think the main cause of the decline of these trees has to do with water and root competition.
How to identify avocado roots
Avocado roots are white or cream-colored if healthy, they do not have fine branchlets (“hairs”), they are about as thick as a spaghetti noodle, they are brittle and easily snapped (not fibrous, flexible, woody), and when snapped they smell like anise (black licorice).
However, when did an autopsy of the GEM and Maluma trees, I found some avocado roots but far more non-avocado roots.
It was mostly oak roots under those trees. I had planted them near a number of oak trees, and the oaks had found the irrigation I was giving the avocados and they proliferated roots there, ultimately stealing so much water and soil space that the the young avocados collapsed.
Young avocado trees cannot handle competition
I’m embarrassed that I hadn’t seen this coming because I’d seen young avocados struggle near competition elsewhere in my yard and in many other yards for years.
Here is the pattern: You plant the tree and it grows well for a few months, or even a year or two, but then growth slows, and the leaves don’t get full size or deep green, and the leaves have brown edges, and then the tree just stops gaining in size. If it is in an inland, hot location like mine, it usually dies off, but in a cooler, coastal location, it usually remains alive and stunted for many years.
You think fertilizer might help, you think it’s not enough water, you think it’s a disease, you think the nursery sold you a bad tree, but no. If you scratch and dig under the tree and find a bunch of non-avocado roots, then that is the main problem.
When I see this competition problem, I see it caused by a specific group of bushes and trees over and over. They are usually native or naturalized types. In other words, they’re known tough guys in our Southern California land.
Examples of plants that I’ve seen strangling young avocados include eucalyptus, live oak, scrub oak, sumac, buckwheat, camphor, various cactuses, pepper trees, grapes, and lawns, especially of Bermuda or St. Augustine.
What can you do?
I know of six ways to manage this situation.
1. Remove the competition. If you do this, then problem solved.
2. Reduce (prune) the competition. If you do this, then problem mitigated. I have done this many times elsewhere in my yard, especially with oaks and sumacs, and if you prune enough and prune soon enough, then the young avocado will still grow although never as well as if the competition were totally removed.
3. Cut competing roots. You can do this with a shovel at planting time, or you can do it anytime after planting. I do it at least once a year for some of my trees, slicing with a shovel just outside of the irrigated zone of the trees. The deeper you cut, the better, but cutting down only a foot is better than nothing.
At a farm in Ventura, I noticed that the avocado trees next to a large live oak were smaller than all the others. The farmer told me that at planting time he had dug a trench to cut all the oak roots. That helped the young trees get established without immediate competition, but since then he had not trenched to cut the oak roots again.
4. Dig a wide planting hole. This gives a new avocado tree more space and time to establish its own root system before dealing with competition.
5. Plant a bigger tree. Rather than a 3-gallon sleeve, you can plant a 15-gallon tree, for example. Such a bigger tree has a bigger root system and can better manage the impending competition. I’ve seen this work in my yard and in others’.
6. Water more and more broadly. Rather than putting a single drip emitter next to the trunk of the tree and giving it as much water as it would need without competition, apply water to a larger area and apply more water than the tree alone needs.
(Read about how this worked for some young avocado trees growing near a pepper tree that suffered from its root competition during a study of drip irrigation on avocado trees in California. “The trees defoliated and looked bad until three more emitters per tree were added by a branched line. Subsequently, the three affected trees returned to excellent condition,” reported Don Gustafson in the 1979 Yearbook of the California Avocado Society.)
Every tree is in a different situation. You might have a neighbor with a giant eucalyptus that you can’t remove, but you can employ all of the other strategies.
For me, I’ve already begun replanting the area of my yard where the GEM and Maluma trees died, but I’m also removing some of the closest oaks, in addition to using some of the other strategies.
And note that older avocado trees cannot win a root competition with tough plants either. It’s just that they are less likely to die from it, and they are more likely to recover if the competition is mitigated. See my Hass tree here:
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