Purple leaves
Purple or reddish leaves and slow growth on young plants, usually from cold soil limiting phosphorus.
What you'll see
- Older leaves and stems turn purple or reddish, often on the undersides, and later dull yellow.
- Growth is slow and stunted, most often on tomato, pepper and cabbage-family seedlings in early spring.
- New growth usually comes in green once the soil warms and roots grow.
Why it happens
Young roots in cold, wet soil can't take up enough phosphorus, even when the soil has plenty. True shortages are rare in gardens but happen in old potting mix and very acid or alkaline soil.
How to fix it
- Move seedlings somewhere warmer, or wait to plant out until the soil has warmed.
- Feed with a balanced soluble fertilizer around the base of the plant, at the label rate.
- Feed container plants regularly, since potting mix runs out of nutrients.
Keep it from coming back
- Harden off transplants and plant out after the soil warms in late spring.
- Test garden soil before adding phosphorus; most soils have enough, and extra can pollute water.
- Some plants are naturally purple, and cabbage-family plants often blush under stress.
Sources
- RHS: Nutrient deficiencies
- Missouri Botanical Garden: Nutrient deficiencies
- University of Maryland Extension: Nutrient deficiency of vegetable plants
General guidance, not a diagnosis. For valuable, edible or outdoor crops, check with a local extension service or plant expert. Use any product exactly as its label says, and keep children and pets away while it dries.