Epsom salts, chemically known as magnesium sulfate, are often used in horticulture to address specific nutrient deficiencies in plants, particularly citrus trees. Magnesium is a component of the chlorophyll molecule, making it necessary for photosynthesis and energy transfer within the plant. This guide provides practical steps for applying magnesium sulfate to citrus trees, ensuring proper dosage and timing to support tree health and fruit production.
Identifying Magnesium Deficiency in Citrus
Visual inspection of the foliage is the first step in determining if a citrus tree requires magnesium supplementation. Magnesium is a mobile nutrient, meaning the tree can relocate it from older leaves to support new growth and developing fruit. Because of this mobility, deficiency symptoms first appear on the mature leaves located lower down on the branches.
The characteristic sign of a magnesium shortage is a pattern of interveinal chlorosis, where the tissue between the veins turns yellow while the veins themselves remain green. This yellowing often creates an inverted ‘V’ or herringbone pattern. In severe cases, the yellowing can progress until the entire leaf turns a bronze or yellow color before dropping prematurely, which can significantly reduce the tree’s vigor and fruit yield. A definitive diagnosis should involve a soil or leaf tissue test to confirm the need for magnesium.
Determining the Proper Dosage and Preparation
Before applying any treatment, it is important to accurately measure the Epsom salts to prevent over-application, which can interfere with the uptake of other nutrients like calcium. Dosage varies significantly depending on the method of application—whether you are using a soil drench or a foliar spray. For a soil drench, a general guideline is to use 1 to 4 ounces of Epsom salts for every cubic foot of soil around the root zone, or approximately 75 grams for a mature tree, applied three times a year.
When preparing a foliar spray, a common ratio is to dissolve one to two tablespoons of Epsom salts per gallon of water. Use warm water and stir thoroughly until the granules are completely dissolved, ensuring the solution is homogenous and preventing crystallization that could clog a sprayer.
Applying Epsom Salts to the Tree
Soil Drench Application
The soil drench method involves applying the dissolved magnesium sulfate directly to the soil where the tree’s feeder roots are most active. Pour the solution around the “drip line” of the tree, which is the imaginary circle on the ground directly beneath the outermost tips of the branches. Applying the solution here ensures it reaches the area where nutrient absorption primarily occurs.
Avoid pouring the solution directly against the trunk of the tree, as this concentration of salts can damage the bark and superficial roots. After applying the drench solution, water the area thoroughly with plain water to help carry the magnesium down into the root zone for uptake. This method provides a slower, more sustained release of the nutrient, which is preferable for long-term correction.
Foliar Spray Application
The foliar spray offers a faster way to deliver magnesium directly to the leaves, providing a quicker visual recovery from deficiency symptoms. To maximize absorption, apply the solution when the weather is calm and the temperatures are moderate, ideally in the early morning or late evening. Avoid spraying during the hottest part of the day or when the tree is under heat stress, as this can cause the leaves to scorch.
Ensure that the spray thoroughly covers both the top and, more importantly, the underside of the leaves, as the stomata—the small pores responsible for gas and moisture exchange—are more numerous there. The magnesium is absorbed directly through the leaf surface, bypassing any soil issues that might be hindering root uptake. Applying a horticultural wetting agent can help the solution spread and adhere to the waxy leaf surface, further enhancing absorption.
Optimal Timing and Frequency
The most opportune time to apply Epsom salts is during the tree’s periods of active growth, typically corresponding to the spring flush of new leaves and early summer when the fruit is actively developing. Magnesium demand increases significantly when the tree is setting and sizing fruit. Applying the supplement before or at the start of these high-demand phases can prevent the onset of visible deficiency symptoms.
For a tree showing clear signs of deficiency, treatment may need to be repeated two to three times annually to correct the imbalance. Once the deficiency is corrected, a maintenance application once per year is often sufficient. Monitor the tree’s response and avoid excessive application, as an overabundance of magnesium can reduce the tree’s ability to absorb other positively charged nutrients, such as calcium and potassium.