Late in the season use an Epsom salt spray to increase tomato and pepper yield and keep plants green and bushy; early in the season add Epsom salt to the soil to aid germination, early root and cell development, photosynthesis, plant growth, and to prevent blossom-end rot.
Epsom salt is a natural mineral compound of about 10 percent magnesium and about 13 percent sulfur—often referred to as magnesium-sulfate. Epsom salt is highly soluble and easily taken in by plants when combined with water and sprayed on leaves. As a soil additive, Epsom salt becomes soluble with soil moisture and is drawn up into plants through the roots.
A magnesium or sulfur deficiency in the soil can cause tomato and pepper plants to grow small and spindly, leaves to yellow between leaf veins late in the season, and fruit to be slow in maturing and ripening.
How to Apply Epsom Salt to Plants
• Foliar spray during the season. Add two tablespoons (42 grams) of Epsom salt to a gallon (3.8 liters) of water and use a tank sprayer to apply the mix once a month substituting the spray for regular watering. Use one tablespoon (21.25 grams) per gallon of water if you apply Epsom salt spray more often than once a month. Begin foliar spraying when blooms first appear.
• Sidedressing during the season. Work one tablespoon (21.25 grams) of Epsom salt per foot of plant height around the base of each plant. Sidedress plants every six weeks beginning soon after leaves appear and continuing through the end harvest.
• Soil additive at planting time. Add one or two tablespoons (21.25–42 grams) of Epsom salt to the bottom of each hole before planting seeds or transplants.
More useful information about magnesium and sulfur:
- Magnesium is critical for seed germination, production of chlorophyll, and fruit development; it helps strengthen cell walls and improves plant uptake of nitrogen, phosphorus, and sulfur.
- Sulfur is critical for the production of vitamins, amino acids and protein, and enzymes.
- Alkaline soils with a pH of 7 or greater and acidic soils high in calcium and potassium often have low levels of magnesium. Calcium and potassium compete with magnesium for uptake by plant roots—magnesium can be blocked from plant uptake by calcium and potassium.
- Dolomitic lime which is used to raise the pH of acidic soils is rich in magnesium (46 percent calcium carbonate, 38 percent magnesium carbonate).
- The soil additive Sul-Po-Mag (22 percent sulfur, 22 percent potassium, 11 percent magnesium) which is often added to alkaline soils should negate the need for Epsom salt.
- Beans, peas, lettuce, and spinach produce good yields in soil with a low magnesium level.
- A soil test will tell you if your soil is nutrient deficient. The cooperative extension service in your area or a private soil testing laboratory can perform a soil analysis.
- Epsom salt is available at the garden center and hardware stores as are most other soil additives.
- Epsom salt gets its name from the town of Epsom in Surrey, England where the bitter salt was first produced from a saline spring.