We have three avocado trees and while they’re doing fairly well, we noticed their leaves started browning on the tips. After looking it up, there weren’t great answers out there, so I did some research to find out more. Here’s what I found about avocado trees and brown leaves.
Avocado trees get brown leaves from under-watering and a buildup of chloride salts in the soil. These salts naturally occur in water sources and avocado trees are more sensitive to them than most other plants. The salts accumulate in the avocado tree’s leaves, which turn brown, starting at the tips.
Before we get into the details, you should know that if 10% of your avocado tree’s leaves are turning brown or dropping—that’s totally normal and their fruit yields shouldn’t be impacted. It’s a natural process for some leaves to be shed to allow for new ones to grow.
However, if more than 10% of your avocado tree’s leaves are turning brown, then read on to find out how we can fix it.
Brown leaves on avocado trees aren’t a new issue. It’s actually been documented since at least 1951.
Leaf burn of avocado is caused by sodium or chloride accumulation in the leaf, or by inadequate water supply.A. D. Ayers, D. G. Aldrich, and J. J. Coony, California Agriculture 1951
Let’s start with the easier of the two issues—a lack of water.
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Avocado trees grow best in USDA hardiness zones 8-11, which typically range from subtropical to tropical. Because of this, avocado trees are normally exposed to hot weather for much of the year. And with a lack of water, they can’t properly cool themselves.
Much like humans, plants breathe and release moisture when hot. For plants, this is called transpiration. When the climate is too hot and dry, the transpiration and root moisture can’t effectively keep up and cool the plant and its leaves. As a result, the avocado tree’s leaves dry, curl, brown, and sometimes drop.
Compared to other fruit trees, avocados are one of the biggest consumers of water. Avocado trees require around 50 gallons of water per pound of fruit (source).
So, what’s the best way to water avocado trees?
Only water avocado trees when their soil is dry. You can check this by pushing a finger 2-4 inches into the soil. If it’s dry, water it. If it’s wet, hold off on watering until it’s dry. Aim to water the soil up to 2 feet deep and provide 2 inches of compost and 4-12 inches of mulch on top of the soil, under the canopy.
The reason why we want to water 2 feet down is that this is the depth for the majority of the avocado tree’s roots.
Most roots are found close to the surface, with 90% or more of all roots located in the upper 60cm [24 inches].Martin Dobson, Arboricultural Advisory and Information Service
So, by watering down to 2 feet, and only watering when the soil is dry, we’re encouraging water independence for the tree and preventing both under-watering and over-watering.
The goal is for the soil to be as wet as a wrung-out sponge.
Additionally, add 2 inches of compost and 4-12 inches of mulch to promote more water independence for your avocado tree.
Compost adds nutrients and organic matter to the soil, with each 1% increase in the soil’s richness absorbing 20,000 more gallons of water per acre (source). On the other hand, mulch dramatically reduces evaporation and provides even more nutrients for your avocado tree.
With these two practices, it’s entirely possible to reduce or even eliminate fertilizer and irrigation (seriously, people are actually doing this).
Reapply the compost every 1-2 months and the mulch every 6-12 months.
But what happens if your soil is properly watered? What else could be causing the avocado tree’s brown leaves?
Chloride Salt Buildup
If your avocado tree is getting watered properly, and it still has brown leaves, it’s most likely due to chloride or sodium buildup (or both).
Chloride is a naturally occurring salt in water (also called table salt).
For example, the water from the Colorado river is high in chloride and supplies much of the southwest with irrigation, drinking, and treatment water.
The problem is that when we irrigate our plants with this water, chloride builds up in the soil. And with evaporation, even more chloride is left behind.
Normally, this wouldn’t be an issue, but avocado trees are particularly sensitive to these salts.
Groundwater and district water chloride values ranged from 84 to 134 parts per million (ppm). Negative effects of chloride on avocado production can be seen at levels above 75 ppm.Adoption of Water-Related Technology and Management Practices by the California Avocado Industry,
University of California Giannini Foundation of Agricultural Economics
Avocado tree roots absorb the extra chloride in the soil and store it in their leaves. When much of their leaf moisture is lost through transpiration, the salts accumulate. At a certain point, the level of chloride becomes toxic for leaves, and their tips brown and die. Over time, entire leaves die.
What’s the Difference Between Chlorine and Chloride?
Chlorine is a bleach and is used in water treatment, from drinking water to irrigation to pools. It’s actually a gas that’s dissolved in the water.
On the other hand, chloride is a naturally occurring chlorine salt, commonly found in fresh and saltwater. For example, the most common form of chloride is sodium chloride, and seawater has about 3% (source).
If you’d like to reduce or eliminate chlorine from your tap water, leave it out for 1-4 days. Since it’s a gas, it will evaporate.
For chloride, there are a few ways to reduce or eliminate it from your soil (and fix your avocado tree’s brown leaves).
How to Reduce Chloride Salts in the Soil
Promote Soil Drainage
If your avocado tree has poor drainage, and the soil is currently wet, hold off on watering until the soil dries a bit or can be amended. Once amended, you can manually dry the soil to prevent mold or root rot if needed.
The bad news is that poor soil drainage creates more evaporation as the water is closer to the surface. And when the water evaporates, it leaves behind chloride salts, eventually building up to toxic levels for your avocado tree.
However, the good news is that providing your avocado tree with sufficient water can also correct chloride buildup (this is called leaching, more on this later).
As avocado trees are natively from the tropics, they prefer sandy soils and plenty of water.
The reason why sand particles are preferred for drainage is that they’re much bigger than clay particles and as a result—allow for water to pass through. On the other hand, clay particles stick together, compacting and preventing water from draining properly.
Sand is also generally acidic, while clay is alkaline. Since avocado trees prefer slightly acidic soil pH of 5.0-7.0 (source), they do best with some sand.
Unfortunately, many gardeners deal with heavy clay soils and often say it’s their biggest challenge.
For example, our backyard has several patches of rich, loose soil as a result of nearby plants and trees shedding branches and leaves, mulching and feeding the soil. However, we still have some spots of isolated heavy clay soil, and we looked into the best way to amend it.
Here’s what we found.
When working with clay soil, digging a hole to plant a tree can often be the wrong move. While it might seem like a good call at the time, the clay hole can serve as a bucket with little to no drainage. When the tree is watered, the water collects and can drown the tree’s roots. Over a short time, this can kill the avocado tree.
So, how do you plant an avocado tree in clay soil?
Plant avocado trees on 1 to 2-foot mounds of soil and add 1-foot of mulch under the canopy. Expand the mound and mulch as the tree grows. You can use many different kinds of mulch, such as leaves, bark, straw, and pine needles.
By planting in a mound, the avocado tree has soil that’s well-draining and loose—perfect for its roots to grow and expand.
If you’d like to learn more about planting in mounds, check out my other post: Can Fruit Trees Grow in Clay Soil (& How To Plant Them)?.
Water The Tree More (Leaching)
Once your soil has well-draining soil, the best way to reduce chloride buildup is to give it more water.
Providing your avocado tree with more water allows the water-soluble chloride salts to dissolve and pass deeper into the soil—out of reach of the avocado tree’s roots. This process is called leaching.
There are two primary ways to leach soil:
- Water lightly for 24 hours straight, once per month in the warm months (July, August, and September)
- Water an extra 10-20% of what you’d normally water. This process is called “leaching fraction”.
Keep in mind to only water the soil, and not the tree’s leaves. If the leaves themselves are watered, leaves can blister in hot weather or diseases can easily be spread from leaf to leaf.
In addition to providing compost and mulch, if you’d like to prevent evaporation even further, consider installing drip irrigation. Most sprinklers shoot water into the air, creating a lot of mist, which quickly evaporates.
However, drip irrigation and sprinklers contribute to salt buildup differently.
Typically, drip irrigation leads to pockets of dense salt while sprinklers create a wider application but with less salt.
As a general rule, drip irrigation works best for young avocado trees with more mature avocado trees do better irrigated with larger volumes of water.
Mature avocado trees are also more water independent as their deeper roots access more groundwater (while also holding more water in the soil).
Again, I’d only recommend leaching your soil if it’s well-draining. Providing extra water in poorly draining soils can make things worse and lead to diseases such as root rot.
Use Soft Water
Another effective way to reduce chloride in your water is to use soft water. Hard water contains hard minerals and salts and is common in most types of water. The process of soft water removes these hard minerals (source).
|Soft Water Examples||Soft Water Examples|
|Most Other Treated Waters||Distilled (steam)|
By watering with soft water, we can often avoid adding chloride to the soil.
How To Test For Salt in Soil
If you believe you have a salt buildup in your soil and would like to test it to confirm, you can send it out to a testing laboratory. For example, here in Texas, you can send your soil sample to the Texas A&M AgriLife Extension Service.
On the other hand, if you’re interested in conducting a salinity test at home, then check out this video by NDSU Soil Health to see how it’s done (I wasn’t able to find the soil salinity tester she used, but I found a similar one on Amazon. It’s a little pricey, but it could be worth if you have a stubborn salinity issue).
If your avocado tree has 10% or less of its leaves browning, I wouldn’t worry about it. However, for brown leaves over 10% of the total canopy, it’s almost entirely due to either a lack of water or a buildup of chloride salts.
Once you find the issue and correct it, your avocado tree should begin growing new leaves quickly.
Start with checking your avocado tree’s watering. Only water when the soil is dry and the goal should be to keep the same moisture as a wrung-out sponge. Using compost and mulch will help immensely.
If you’re watering properly and your avocado tree is still getting brown leaves, it’s probably from the chloride. In this case, promote more soil drainage, perform leaching, and use soft waters if you can.
Other, less common issues that can contribute to brown leaves on avocado trees are excess fertilizer and pests and diseases. Typically, symptoms of pests and diseases are yellow or brown spots on leaves.
If you believe you’d over-fertilized, consider leaching the fertilizer further into the soil (the same method as leaching the chloride mentioned above).
While it can be difficult to figure out which fertilizer is good for your avocado tree, I recently did some research and testing of some of the best fertilizers. You can see my post where I review the best avocado tree fertilizers.
If you’ve tried the above steps in this post, and you still aren’t sure what’s causing the brown leaves on your avocado tree, my recent post here helps troubleshoot avocado trees and their common conditions: How To Revive a Dying Avocado Tree (3 Quick Steps).