Growing healthy, vibrant avocado trees requires a clear understanding of their growth patterns and the fertilizers needed. Avocado fertilizers should be applied to the effective root zone, which is typically the top 30 cm of soil, to ensure nutrient utilization efficiency. Avocado trees are subtropical evergreens that are never dormant, although their activity slows down in winter compared to spring and summer. These trees belong to the Lauraceae family and come in three horticultural races: West Indian, Guatemalan, and Mexican, each adaptable to various soil and climate conditions.
Among the three horticultural races, the West Indian variety is most susceptible to low temperatures, while the Mexican variety is the coldest hardy. Planting avocado trees in frost-free areas, such as slopes with good air drainage is best. Additionally, avocado roots are sensitive to poor aeration, so avoid planting them in heavy, compact soils with poor permeability.
Research shows that for a ‘Hass’ avocado yield of 30 tons per hectare, the nutrients removed are 120 kg of Nitrogen (N), 25 kg of Phosphorus (P), and 240 kg of Potassium (K). To achieve high-quality yields, the recommended annual quantities of nutrients are 250–300 kg/ha of Nitrogen, 80–120 kg/ha of Phosphorus, and 500–600 kg/ha of Potassium.
Major Avocado Fertilizers
Before applying any fertilizer, it’s essential to assess the specific needs of your avocado tree. Young trees, for example, require nutrients to support rapid growth, particularly nitrogen for leaf and stem development. Mature trees, on the other hand, benefit from a balanced approach that supports both the tree’s structure and fruit production. Observing your tree’s growth patterns, leaf color, and overall health can provide initial clues to its nutritional needs.
The type of soil affects how avocado plants should be fed. Rather than giving the tree direct access to the nutrients it needs, we fertilize to compensate for any nutrient deficits in the soil. Avocado trees require well-aerated soil since they are shallow-rooted plants, with the majority of their feeder roots located in the top 6 inches (15 cm) of the soil.
Conducting a Soil Test: The most reliable method to ascertain these requirements is through a professional soil test. This test will identify nutritional deficits in addition to your soil’s pH level. A pH of 6.0 to 7.0 is preferred for avocado plants, which are slightly acidic to neutral. Regardless of the fertilizer used, nitrogen uptake may be impacted if the pH is outside of this range.
Here is the list of major fertilizers for better yield of avocado.
Mycorrhiza
The absence of root hairs in avocado trees results in their heavy reliance on mycorrhiza for food. These fruit trees are colonized with fungi that generate arbuscular mycorrhiza, which improves nutrient and water uptake while also encouraging plant development and general health. With the help of these fungi, which develop into a broad mycelial network in the roots, plants can better withstand environmental stress such as salt, drought, acidic soils, the presence of toxic substances, and root infections, as well as boost their uptake of phosphorus (P), copper (Cu), and zinc (Zn).
According to recent research, mycorrhizal fungi greatly accelerate the growth of avocado seedlings. By enhancing the absorption of vital mineral nutrients like phosphorus, zinc, and copper, these fungi benefit their host plants. It’s remarkable that seedlings with mycorrhizal relationships may get enough phosphorus from untreated soil. Mycorrhiza increases the concentration and content of nitrogen (N), phosphorus (P), and potassium (K) in plant tissues.
Compost
Composted organic matter, chicken manure, and well-rotted cow manure are excellent sources of slow-release nutrients. They improve soil structure, enhance microbial life, and provide a wide range of essential nutrients for a long time.
Nitrogen (N)
Nitrogen is considered to have a great influence on the growth of the avocado tree and is therefore commonly used.
Nitrogen is the most widespread deficiency in avocado orchards. Nearly all orchards require some nitrogen fertilization each year to maintain normal yields. Nitrogen should be applied to the tree every year to maintain optimum production.
The fertilizer schedule would be applied in three split doses in late February or early March, in June, and the remaining in September.
| Age of Tree (Year) | Dose of Nitrogen (N) |
| 1 | 1 tablespoon i.e 14 g |
| 2 | 57 g in three split doses |
| 3 | 114 g in three split doses |
| 4 | 227 g in three split doses. |
| 5 | 340 g in three split doses. |
| Over 5 | 450-1000 g in three split doses. |
Nitrogen is crucial for the growth of avocado trees and is commonly used to address widespread deficiencies in avocado orchards. Most orchards require annual nitrogen fertilization to maintain normal yields and optimum production. A good hand-applied fertilizer schedule involves applying nitrogen in three split doses: late February or early March, June, and September. In the early years of avocado production, a single soil nitrogen application was made between January and March, or it was split between January and June or July.
To protect groundwater from potential nitrate pollution, avocado growers are encouraged to apply the total annual nitrogen in six small doses, about every other month starting in January. This schedule does not consider changes in nitrogen demand associated with different stages of tree phenology. ‘Hass’ trees need more fertilizer than ‘Fuertes,’ probably twice as much. It is suggested to change or rotate materials every two years, for example, using ammonium nitrate for two years, urea for the next two, and ammonium phosphate in the fifth year. Nitrogen may be applied once or twice a year on mature trees, ideally in February and July. Fertilizing during the blossom and fruit setting period from March through June is not recommended.
For young plants, no fertilization is necessary until their root systems are fully developed. Afterward, abundant fertilization is essential, especially on light soils, to achieve rapid development. The yearly nitrogen amount for young trees should be 30-40 grams per tree in the first year, 80 grams in the second year, 160 grams in the third year, and 200 grams in the fourth year. This fertilizer can be divided into two parts, with about a third applied in early spring and the remainder in mid-summer.
Phosphorus (P)
Phosphorus should be applied pre-flowering and continuously throughout the flowering stage until the end of harvest, as flowering requires high metabolic energy. Biweekly applications of Zn support the production of auxins, which are crucial for synthesizing nucleic acids, proteins, and vitamin C, thereby aiding fruit setting. It is advised to avoid high potassium (K) fertilization until 60 days after full bloom, as it might repel bees from the flowers.
Excess phosphorus (P) can cause zinc (Zn) deficiency symptoms, although avocado plantations generally do not exhibit clear P deficiency symptoms. Even when low P levels in leaves are corrected with fertilization, the effect on yield is negligible. However, it remains a common practice to apply P fertilizer to avocado plantations on poor soil.
Potassium (K)
To increase fruit size and improve quality, ample amounts of potassium are required during fruit development. Potassium also enhances plant water management and drought tolerance in warm weather. Deficiency symptoms appeared only after eight years in trees grown in sand culture without receiving any potassium (K). The leaves were small and narrow, and in autumn, brownish-red necrotic spots began to appear on older leaves, eventually spreading over the entire leaf blade between the large veins. Severely deficient trees had very thin twigs, and some dieback occurred.
Zinc (Zn)
Zinc deficiency, commonly referred to as mottle leaf, is a prevalent issue in avocado trees, being the most frequently recognized micronutrient deficiency. This deficiency results in reduced tree vigor and lower yields, and if left uncorrected, can ultimately lead to tree death due to a lack of zinc. While foliage spray can be applied at any time of the year, it is most effective when done in early spring. An effective spray mixture consists of 1 pound of zinc sulfate (36% zinc) per 100 gallons of water. However, it is crucial for growers to understand that more zinc does not necessarily mean better results; excessive zinc levels can waste resources or even reduce yields.
Soil application of zinc sulfate (36% Zn) is beneficial, particularly for acid-type soils and situations where spray rigs cannot access the orchard due to crowded trees or steep terrain. Although soil treatment has a slower response compared to foliage spray, its effects are more prolonged, lasting up to five years, whereas spraying needs to be done annually or biennially. Soil application can be done at any time of the year. However, phosphorus should be continuously applied from the pre-flowering stage to the end of the harvest to meet the high metabolic energy requirements. Biweekly zinc applications support the production of auxins, which are crucial for the synthesis of nucleic acids, proteins, and vitamin C, thereby aiding fruit setting.
| Age of Tree (Year) | Dose of ZnSo4 (36% Zn) per tree |
| 2 | 375 g |
| 5 | 907 g |
| 7 | 1180 g |
| 10 | 1497 g |
| 15 | 2404 g |
| 20 | 3040 g |
Calcium (Ca) & Boron (B)
Calcium deficiency or excess in leaves can indicate interference in the uptake of other elements. Symptoms of calcium deficiency sometimes resemble those caused by Phytophthora cinnamomi, as both lead to the collapse and disintegration of the root system. However, in cases of calcium deficiency, the roots can regenerate, whereas plants affected by Phytophthora experience root disintegration followed by loss of leaf turgor and much faster dieback. Research suggests that maintaining high calcium levels in soils can reduce the severity of root rot by improving soil structure. Additionally, calcium helps roots resist infection by Phytophthora cinnamomi, which causes avocado root rot.
During the early stages of fruit development, when evapotranspiration through the fruits occurs, it is recommended to provide more calcium than potassium and to avoid applying ammonium-nitrogen, as it may interfere with calcium uptake.
Boron is also important, as it supports the transportation of sugars, the internal regulation of growth hormones, and other physiological processes. Moreover, boron is being studied for its potential role in improving fruit set in avocado trees. Known for its importance in pollen germination, boron supports the growth of the pollen tube, enabling successful fertilization by guiding the pollen through the stigma, style, and ovary to the ovule. Studies have shown that applying boron sprays to trees—particularly those that are not deficient—during fall or spring can significantly improve fruit set, especially under cooler temperatures. This practice has proven effective for various deciduous fruit trees, as boron helps with critical reproductive processes.
In trials, avocado trees treated with foliar boron showed enhanced pollen germination and pollen tube growth compared to untreated trees, even when untreated trees had adequate boron levels for normal growth. This suggests that additional boron application, particularly targeting reproductive structures, may benefit fruit set regardless of overall plant health.
Iron (Fe)
Iron is crucial for chlorophyll synthesis in plants, and deficiencies typically occur in alkaline soils rich in calcium carbonate, as well as in overly wet and cold conditions. Although iron is naturally present in most soils, its availability to plants diminishes with higher soil pH. Iron deficiency can often be addressed by reducing irrigation frequency or avoiding waterlogging, as these conditions reduce iron solubility and accessibility to plants. Foliar sprays containing iron chelates are effective in correcting iron deficiency when applied directly to plant leaves.
When to Fertilize Avocado Tree?
It is recommended to apply fertilizers three times during the growing season: once in early spring, second in mid-summer, and next in autumn aligning with the periods of active growth in trees. Regarding the distribution of fertilizer, the application rates should be divided according to the following schedule:
Early Spring
As soon as new growth appears, it is best to apply a balanced fertilizer solution for the first time. Test the soil for specific nutrient shortages and make any necessary adjustments to the fertilizer composition depending on the findings. Furthermore, it would be wise to think about using a foliar treatment at this time to properly address any nutritional deficiencies if your trees showed symptoms of such last season.
During the active growth season
To encourage further fruit development and overall tree growth, stick to a schedule of nitrogen-rich fertilizations every 4-6 weeks for follow-up treatments. The health and production of the tree depend on these routine applications. Prioritizing enough water is crucial, especially after fertilizing, since this allows the tree to absorb nutrients more efficiently and use the nutrients from the fertilizer more efficiently for healthy growth and fruit production.
Autumn
Apply the final fertilizer application by late summer or early fall to prevent promoting new growth that won’t be able to survive the winter months.
How to apply Avocado Fertilizers?
For the best results, make sure to fertilize your avocado plant evenly. To prevent damage, apply fertilizer in a circle around the tree’s base, keeping away from the trunk. Consider this as shaping a doughnut, with the roots assiduously absorbing nutrients like customers at a counter and the trunk serving as the hole. The drip line, or the outside edge of the canopy where rainfall naturally falls from the leaves, is where it’s crucial to uniformly distribute the fertilizer. This method encourages the formation of outer roots, which improves the stability and nutrient uptake efficiency of the tree. Fertilizer shouldn’t be applied too near to the trunk to avoid root burn and possible tree damage.
FAQs
Q1. What is the best N-P-K ratio for avocado trees?
For avocado plants, the optimal nitrogen-phosphorus-potassium (N-P-K) ratio usually falls between 8-3-9 and 10-5-15. Moderate nitrogen levels are beneficial to avocado trees because they encourage healthy growth of leaves and stems. On the other hand, too much nitrogen may cause too much vegetative growth at the expense of fruit production. Potassium supports fruit development, quality, and the tree’s resilience to stress, whereas phosphorus is essential for root growth and general plant vitality. Selecting a fertilizer that is well-balanced and supplies these nutrients in the right amounts promotes healthy growth and fruit. Maintaining sustainable and productive orchards requires modifying the fertilizer mix according to soil test results and the unique requirements of the avocado trees.
In terms of application rates, mature avocado trees typically require around 0.5 to 0.8 kg (1 to 1.8 lbs) of actual nitrogen, 0.19 kg (0.42 lbs) of phosphorus, and 0.75 kg (1.65 lbs) of potassium per year for optimal yield when using synthetic fertilizers. Farmers should consider these guidelines when applying fertilizers to ensure the nutritional needs of avocado trees are met without causing nutrient imbalances or environmental harm. Adjustments in fertilizer application should be made based on factors such as soil conditions, tree health, and fruiting patterns observed throughout the growing season to achieve sustainable production and maintain the health of avocado orchards over time.
Q2. Is potash good for avocado?
Yes, throughout the summer, avocado trees use a lot of potassium, especially when the fruit grows and ripens. The plant absorbs potassium in the form of potassium ions (K+), which stay in their ionic state after being absorbed from the soil solution. This nutrient is essential to the physiology of the plant because it controls how guard cells open and close stomata, which improves the efficiency of water usage. Furthermore, potassium helps trees grow strong roots, improves disease resistance, encourages the production of larger, higher-quality fruit, and strengthens the tree’s resistance to winter weather.
Q3. How do you increase the yield of an avocado?
The following procedure should be followed to increase the yield of avocados:
- Plant density
Maintain proper plant density and spacing to maximize air circulation and sunlight exposure.
- Pruning
Frequent pruning increases fruit output and encourages a balanced canopy.
- Irrigation
Sufficient irrigation is beneficial for optimum growth, especially during fruit set and development.
- Balanced fertilizers
Fertilizers mentioned above in this article are recommended to apply to the avocado tree to boost the yield.
- Bees
Bee increases the fruit set in the orchard.
- Girdling
Girdling in October encourages the development of flowers and strengthens them, making them more resilient to stress than blossoms on ungirdled trees.
