The Big Mystery of Small Avocados: Solved!

Growing your own avocado tree can be incredibly rewarding when you’re able to reap a plentiful harvest. However, if your garden-grown avocados have been disappointingly small in size you’ll want to solve the mystery of small avocados. Read on to find out.

Avocados Growing on the Tree
Small Avocados Growing on the Tree

Why Are My Avocados So Small?

The most common causes of small avocados are stress, root rot, high temperatures, and lack of zinc.

Let’s take a closer look at the factors that can cause your avocado tree to produce small fruits, and how you can fix these problems.

1. Avocado Tree Stress

Stress is one of the main reasons why an avocado tree (Persea Americana) will produce small and undeveloped avocados. The development of a fruit can be divided into two stages; the first stage is the creation of the fruit (cell division), and the second is the expansion of the fruit (cell expansion).

An avocado seed coat produces auxins (hormones that create cell division) which prompts the continual formation of new cells from the inside of the fruit. When an avocado tree becomes stressed the seed coat in its fruit begins to die which prevents the fruit from fully developing.

Avocado trees become stressed due to abiotic environmental factors such as nutrients deficiency in the soil, high and low temperatures, and the salinity of the water that it receives. Other causes of stress can be attributed to pest and rodent infestations, as well as bacterial infections.

Your avocado tree naturally produces antioxidants as a way to combat stress. Increasing the antioxidants in your soil will assist your avocado tree in protecting the cell membranes of the fruits.

Adding organic humic acids to your soil increases the level of antioxidants that are available for your avocado trees. Calcium is a secondary nutrient that improves your plants’ reaction to stressful conditions. I’ve found that feeding my avocados with an organic fertilizer like this one which includes all the nutrients the soil needs, helps in producing larger avocados.

Small Avocados on the Tree
Small Avocados on the Tree

2. Avocado Root Rot

Avocado trees are vulnerable to diseases, including the most common one: root rot. Root rot will cause your avocado tree to lose foliage and produce small fruits. This multi-fungal infection will enter the rooting system of your avocado tree when your tree is watered, or when the roots sit in soil that is too damp.

Watering the roots of your avocado tree, specifically after a dry period (drought), will cause the roots of your tree to burst open. Once root rot has infiltrated the system, it will begin to decay the roots. One of the first signs of root rot is the drooping of your avocado tree’s leaves, and the premature dropping of its fruits.

Watering your avocado tree on a regular basis will prevent it from experiencing drought stress (and consequently root rot), but be careful not to overwater your tree. Remove any excess organic debris surrounding your avocado tree (if it is more than 4 inches deep) as it retains moisture. This will then lead to overly wet soil.

Ensuring your avocado tree is planted in soil with excellent drainage is one of the best ways of avoiding root rot. One effective method is to mound up the soil before planting, so you are creating a small hill and then plant your avocado tree at the top of your mound. That way, water will not pool in the soil and will instead drain away from your avocado tree roots and prevent the possibility of root rot.

Using organic fungicides and biological control agents like Trichoderma can be an effective method in preventing root rot. However once root rot has taken hold, it can be very difficult to fix organically or even with chemical treatments. 

3. High Temperatures

Avocados are a subtropical fruit that grows best in a climate ranging between 65°F-85°F (18-29 °C). However, avocados can withstand higher temperatures for a short time period, but when temperatures begin to exceed the avocado tree’s limits, the tree will begin to “feel the burn”.

When temperatures start to climb above 90°F (32°C), the stomata (pores on the leaves), which allow your plant to breathe, will begin to close. Heat waves that occur during early March (the beginning of spring) can damage the growth of your avocado tree and cause it to prematurely drop its young fruits.

Young Avocado Fruit
Young Avocado Fruit

As the weather is unpredictable, there are several precautionary measures you can take to protect your avocados from heat stress. Overwatering avocado trees is never a good idea, although when it’s warmer outside, additional watering of your avocado tree can reduce the effects of heat stress.

Whitewashing the branches and trunk of your avocado tree with a white latex paint will act as a sort of sunscreen for the tree. Sprinkling kaolin clay powder on the leaves of your avocado tree will also protect them from sunburn.

Providing shade for young avocado trees will prevent them from dropping their underdeveloped avocados. I recommend enclosing your avocado trees with 30% shade cloth which can easily be adjusted or removed as the tree grows.

4. Lack of Zinc

Zinc is an essential micronutrient that plants require as it helps in the synthesis of proteins and the formation of chlorophyll. A deficiency of zinc in the soil is a major contributing factor to avocado trees producing smaller, rounder fruits.

Using poultry manure and fertilizer with high levels of phosphorus has been found to cause zinc deficiency in soils. This is due to the reaction of the phosphorus and soluble zinc (in the soil) resulting in an inaccessible, insoluble zinc-phosphorus compound that the plants cannot utilize.

Zinc deficiency occurs more frequently in wetter, colder years compared to years that are warmer and drier.

The level of zinc in your soil can be measured by using a soil testing kit. If you find that this level is less than 15 ppm (parts per million), your soil is considered to be lacking in zinc. A healthy zinc-level in the soil is approximately 30 ppm.

You can solve zinc deficiency in your soil by sprinkling ½ a pound of zinc sulfate around the base of your avocado trees. This quantity will be sufficient for a 12-month period. Your avocado tree will need between 3 to 4 pounds of zinc sulfate over a 5-year period.

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