Why Do My Marigolds Have Purple Leaves?

At first, I didn't think much of it. Some plants have purple leaves. I thought, maybe marigolds get them too and I never noticed. No big, right? Wrong. Or, at least maybe wrong.

I did some digging and found that the reason marigolds, and other plants, develop purple leaves is due to a lack of phosphorous. This can mean that either the soil itself is not rich in phosphorous or the plant is unable to absorb phosphorous efficiently.

With marigolds, cold weather can keep them from absorbing phosphorous. Here in Missouri, it has been in the mid-70s to low 80s since I set out the plants, but at night it is dipping into the low 50s, which could at least partially explain the problem.

If it is warm and your marigold leaves are turning purple, the problem is very likely within the soil. It is possible to aid the flowers by using a fertilizer, but the best way to combat this problem is with prevention rather than cure. That means that next year, add phosphorous prior to planting. However, you should first test your soil so that you know how much phosphorous it needs. While too little will lead to poorly growing plants, too much can block the vital absorption of zinc, iron, and cobalt - all of which are needed for plant development.

Update: Since I first did research into purple leaved marigolds, I read a couple of more blog posts about how to "cure" the leaf color. One suggested that, with time, when the soil warms, it will correct itself. Another stated that epsom salts can raise the level of magnesium in the soil, which aids in the absorption of phosphorous. I am pleased to report that my marigolds are beginning to turn green again, though whether it's due to the warming weather or the epsom salt, I cannot say.