Growing avocado trees can be an extremely rewarding process…for the gardeners who are willing to put in the work. Avocado trees require a good deal of water, but they are also prone to root rot and other fungi and diseases that are associated with soggy soils. Irrigating your tree can be a delicate balancing act!
Recognizing the signs of underwatering is a good first step toward protecting the health of your tree, but it’s just as important to know how not to correct underwatering. For avocado trees, proper irrigation techniques vary by the age of the tree, seasonal temperatures, and tree size.
Signs of Minor Drought Stress
There are several early warning signs that your avocado tree may need more water, including the following:
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- Dieback on terminal branches. This is also known as “staghorning.”
- Flagging leaves
- Yellowing leaves
- Abundant flowering
- Sunburned fruit
If you notice one or more of the above signs, give your tree some water. It should start to revive after a couple of days. Going forward, make irrigating your tree a regular part of your gardening routine.
If your tree doesn’t start to perk up, however, test your soil for the fungus that causes root rot. Root rot causes many of the same symptoms as underwatering because it kills the roots that provide ample water to the tree. Unfortunately, if root rot is your tree’s issue, there is almost nothing you can do to save your tree (source).
Long-Term Consequences of Underwatering
It’s important to correct underwatering as soon as you notice it because the long-term consequences can be severe. There are several diseases associated with drought stress, including:
- Avocado black streak (ABS)
- Bacterial canker
- Stem and leaf blight
Avocado Black Streak
ABS is a common disease that attacks avocado trees’ trunks and branches. Many of the symptoms, including poor growth, yellow leaves, and leaf drop can be attributed to other causes, as well. A surefire way to diagnose ABS is to look for cankers.
The cankers caused by ABS exude a dry, sugary substance. When removed, you will find reddish-brown lesions underneath.
If you catch it early, you can treat ABS by improving your irrigation methods and protecting your tree from further stress. If ABS becomes severe, it will eventually kill your tree.
The great news is that ABS is completely preventable if you avoid underwatering and drought stress altogether (source).
Bacterial canker is caused by the bacteria Xanthomonas campestris, which lives quite harmlessly on many avocado trees. It can infect wounds on the tree’s bark, but underwatering–especially over prolonged periods–increases the severity of the infection.
Usually, bacterial canker presents itself as dark brown or black sunken areas on the bark that range from one to four inches in size. Cutting away the bark reveals decayed wood that may ooze liquid.
For mature trees, bacterial canker is usually not deadly, although affected branches might not produce as much fruit. Often, the cankers will heal once the tree receives sufficient water on a regular basis (source).
Stem and Leaf Blight
Stem and leaf blight is caused by a fungus that leads to decay and defoliation. Early signs include dieback, leaf blotching, and a thinning canopy. If the tree loses enough leaves, the fruit will likely be sunburned.
The fungus that causes stem and leaf blight thrives in drought conditions, so this is another problem that you can prevent through consistent irrigation.
If your tree is experiencing stem and leaf blight, prune off dead tissue and adjust your watering routine. Most of the time, this will be enough to restore the health of your tree.
What Not To Do To Correct Underwatering
When you notice signs of drought stress, it’s natural to want to correct the problem by giving your avocado tree as much water as possible as quickly as possible along with a hefty dose of fertilizer. This approach, however, may create more problems than it solves.
It’s very easy to over-correct for drought stress, especially if your tree’s symptoms are moderate to severe. Here are some common “don’ts” to avoid with your underwatered tree.
- Don’t water every day. Avocados are sensitive to overwatering as well. In fact, many diseases like root rot are associated with too much water and too little airflow.
- Don’t water immediately after a rainfall. Let the soil dry out first, even if the rainfall didn’t seem heavy, and even if it’s been several days since you irrigated.
- Don’t use fertilizers to cure drought stress. Excess fertilizing can add too much chloride and sodium to the soil, which will create a whole other problem for you to solve (source).
Proper Irrigation Techniques
There is no “one size fits all” approach for watering your avocado tree. Your routine will vary based on the age of your tree, seasonal temperatures, and the size of your tree’s canopy.
In all cases, timing and consistency are the most crucial factors. Establishing a consistent watering routine is one of the best actions you can take to keep your tree healthy and thriving.
Furthermore, in every stage of the tree’s life, it’s important to let the soil dry out before watering again. You can test the soil’s dryness by taking a handful from near the base of the tree. If the soil keeps its shape when you squeeze it, it still contains plenty of water.
Avocado trees are considered “young” if they are three years old or younger. Younger trees can’t store as much water as mature trees, so you will need to water them more often.
You should water recently planted trees frequently, at least once or twice a week, for the first eight weeks after planting.
During periods of low rainfall (five or more days without precipitation), your young tree will need about two gallons of water two or three times a week. During rainy periods, let the soil dry out before giving your tree more water (source).
As your tree matures, most of its roots will extend parallel to the ground, rather than straight down into the soil. Because avocado roots are so shallow, they can’t store vast amounts of water from rainfall alone, so you will still need to irrigate them.
During the growing season, mature avocado trees need about two inches of water per week. This may not sound like very much water. However, one inch of rain provides 0.623 gallons of water per square foot–and your tree’s root system will collect water from a much larger area than one square foot (source)!
If you live in an area that doesn’t receive that much rainfall each week, plan to water every seven to ten days. Water slowly, so that no puddles are left on the surface. Furthermore, you should water thoroughly across the entire area covered by the canopy, so that all parts of the root system have enough.
When temperatures are below 90℉, your tree may use 20 gallons of water per day from the soil (source). Unfortunately, in many avocado-growing zones, temperatures do not stay below 90℉ in the height of summer.
Avocados are not particularly heat tolerant, but you can shield them from significant damage by boosting their water supply during heat waves.
You can start preparing for heat waves in the spring by establishing a consistent watering routine that promotes your tree’s overall health. Mulching the ground beneath your tree helps, too. Mulch keeps soil temperatures cool and helps retain moisture.
The day before a predicted heatwave, give your tree one and half times its usual amount of water. Throughout a lengthy heatwave, your tree will benefit from small amounts of water each day, in addition to regular deep irrigation, to keep its shallowest roots from drying out.
Avocado trees can grow very large, and the larger your tree, the more water it needs. If you prune your tree so that it stays around 15 feet, your tree’s water needs will be much more manageable.
It’s good practice to consult a professional arborist before pruning large trees.
If you notice signs of underwatering or drought stress, make it your mission to establish a routine of watering your tree slowly and thoroughly. Consistent, thorough irrigation is critical to preventing disease, promoting vigorous growth, and remaining healthy and productive for years to come.