Epsom salt, known chemically as magnesium sulfate, is a compound gardeners often use to address specific nutrient imbalances in trees. This substance provides two secondary macronutrients: magnesium, which is necessary for photosynthesis, and sulfur, which is needed for the creation of amino acids and proteins. Because application rates vary widely based on the tree’s size and the chosen delivery method, understanding the precise dosage is important for effective treatment.
Identifying Magnesium Deficiency in Trees
The primary reason to use Epsom salt on trees is to correct a confirmed or strongly suspected magnesium deficiency. Magnesium is a mobile nutrient within the plant, meaning the tree moves it from older leaves to newer, actively growing ones when supplies are low. This movement causes deficiency symptoms to appear first on the older, lower leaves.
The most common visual symptom is interveinal chlorosis, where the tissue between the leaf veins turns yellow while the veins remain green. Deficiency can also cause leaves to develop reddish or purplish hues. Severe deficiency can lead to premature leaf drop, stunted growth, and poor production of flowers or fruit. Epsom salt is not a complete fertilizer and should only be used when a deficiency is present, as excessive magnesium can interfere with the uptake of other nutrients like calcium and potassium.
Recommended Application Methods
Epsom salt can be delivered to trees through three main methods, each offering a different rate of nutrient absorption:
- Soil drench: Dissolving the salt in water and pouring the solution directly over the root zone. This allows the magnesium sulfate to be absorbed by the roots, providing a steady, long-term supply of nutrients.
- Granular or dry application: Spreading the crystals directly onto the soil surface around the tree’s drip line. The salt is slowly dissolved by rainfall or irrigation, making this a slower but longer-lasting treatment.
- Foliar spray: Spraying a diluted solution directly onto the leaves. This offers the fastest absorption and a quick visual fix, but the effect is temporary since the nutrient is not stored in the soil.
Precise Dosage Instructions
The dosage of Epsom salt is determined by the size of the tree and the chosen application method. For established, large trees, a granular application is measured based on the root zone area. Apply about two tablespoons of dry Epsom salt for every nine square feet of soil over the root zone, which extends to the tree’s drip line. For very large trees, use one to two pounds per nine square feet around the base, ensuring it is watered in well.
For smaller, young trees and shrubs, apply one tablespoon of dry Epsom salt for every foot of the plant’s height, spreading it within the root area and watering thoroughly. When using a soil drench, dissolve one to two tablespoons of Epsom salt per gallon of water.
For a foliar spray, mix one to two tablespoons of Epsom salt into one gallon of water. The spray should fully coat the leaves, but apply it during the cool parts of the day to prevent leaf scorching. Avoid exceeding these recommended rates, as high concentrations can cause salt burn or create a nutrient imbalance that inhibits the uptake of other elements.
Timing and Frequency of Treatment
The best time to apply Epsom salt is in the early spring, just before new growth begins, or in the late fall after the leaves have dropped. Applying it before the growing season allows the tree to readily use the magnesium for active growth and chlorophyll production. Fall applications allow the minerals to slowly dissolve and become available in the root zone over the winter.
Frequency depends on the deficiency severity and the method used. A soil application for an established tree is recommended once a year, or a maximum of three times annually. A concentrated soil drench can be applied monthly during the growing season until symptoms resolve, and foliar sprays may be repeated every two to four weeks. Avoid treatment during peak summer heat or drought stress, as adding salts can worsen dehydration.