Why Geranium Leaves Turn Red and How to Fix It

If you start geraniums from seed in a Zone 4 garden like Iowa, you may notice the leaves turning a bright purplish-red before transplanting outdoors. This discoloration often signals a magnesium deficiency, a common issue in container-grown seedlings. The good news? It’s easily corrected.

Understanding the Cause

Geraniums (Pelargonium spp.) are heavy feeders, and when grown in soilless mixes, they can quickly deplete available magnesium. Cool spring temperatures and limited root space exacerbate the problem, causing older leaves to develop reddish-purple margins while the veins stay green. The plants usually survive, but they look stressed and may lag after planting out.

Simple Solution: Epsom Salts

Epsom salts (magnesium sulfate) provide a quick, inexpensive magnesium boost. Dissolve 1 tablespoon per gallon of water and apply as a soil drench every two weeks until the foliage greens up. Alternatively, sprinkle 1 teaspoon around the base of each plant at transplant time and water in well. This practice also benefits roses and tomatoes—adding Epsom salts to tomato planting holes helps prevent blossom-end rot and encourages larger fruit.

Prevention Tips

• Use a balanced fertilizer with micronutrients, including magnesium.
• Avoid overwatering, which leaches nutrients from the root zone.
• Harden off seedlings gradually before moving them outside.

With a little magnesium, your geraniums will green up quickly and perform beautifully all season.