How to correctly use Epsom salt on cucumber and tomato plants

The idea

Epsom salt is magnesium sulfate, which provides magnesium and sulfur to plants. To use it, mix one tablespoon of Epsom salt per gallon of water. For example, you can add two tablespoons to a two-gallon watering can. Once dissolved, pour the solution around the base of your plants, soaking the soil to ensure it reaches the roots.

Why it works

Magnesium and sulfur are secondary macronutrients that plants need, but in much smaller quantities than primary macronutrients like nitrogen, phosphorus, and potassium. Over-supplying magnesium and sulfur can be detrimental, as it can "lock out" your plant's ability to absorb other vital nutrients from the soil.

If you regularly use compost and mulch, your plants likely already receive sufficient magnesium and sulfur. Therefore, Epsom salt should not be used as a routine, weekly, or monthly application. It is most beneficial when plants are heavy feeders (like cucumbers, melons, zucchini, squash, and tomatoes) and when grown in containers, where nutrients are more quickly depleted. Do not use Epsom salt as a cure-all for yellowing leaves, as this is often a sign of nitrogen deficiency, not magnesium.

Try it

1. Mix 1 tablespoon of Epsom salt per gallon of water. Ensure the salt is fully dissolved.
2. Apply this solution at planting time for heavy-feeding plants like cucumbers and tomatoes.
3. For established heavy-feeding plants, especially those in containers, apply the solution once mid-season.
4. Pour the mixture slowly around the base of the plant, allowing it to soak into the root system.

Watch out for

• Over-application: Do not use Epsom salt too frequently or in excessive amounts. Too much magnesium and sulfur can prevent plants from absorbing other necessary nutrients.
• Not a complete fertilizer: Epsom salt only provides magnesium and sulfur. It does not supply the primary macronutrients (nitrogen, phosphorus, potassium) that plants need in larger quantities.
• Misdiagnosis of yellowing leaves: Yellowing leaves are often a sign of nitrogen deficiency, not magnesium deficiency. Address primary nutrient needs first before resorting to Epsom salt.
• Soil health: If your garden soil is already rich in organic matter from compost and mulch, your plants may not require additional magnesium or sulfur from Epsom salt.