Why Are My Marigold Leaves Turning Yellow?

Yellow leaves on marigolds are one of the most common complaints, and they usually point to a problem at root level rather than above ground. Waterlogged soil, a nutrient shortage, or the early stages of a fungal disease are the three most likely culprits. Identifying which one you're dealing with takes only a few minutes of observation.

Overwatering and Waterlogged Roots

This is the single most common cause of yellowing in marigolds. Push a finger 5 cm into the compost or soil. If it feels wet and cold, you are watering too frequently. Marigolds prefer to dry out slightly between waterings. In waterlogged conditions roots suffocate and can no longer supply nutrients, so lower leaves yellow first, then the problem climbs the stem. Allow the soil to dry out, improve drainage if needed by adding grit, and water only when the top few centimetres are dry.

Iron or Magnesium Deficiency

Yellowing between the leaf veins while veins themselves remain green (interveinal chlorosis) usually indicates an iron or magnesium deficiency. This can happen in alkaline soils where these nutrients are chemically locked. Test your soil pH — marigolds prefer slightly acidic to neutral (6.0–7.0). If pH is too high, apply sulphur chips to lower it gradually. A foliar spray of chelated iron or a dose of Epsom salts (magnesium sulphate) dissolved in water often reverses the yellowing within two weeks.

Natural Lower-Leaf Senescence

As marigolds mature, the lowest leaves naturally yellow and die off — this is normal ageing, not disease. If yellowing is confined to just the bottom one or two leaves on an otherwise healthy plant, simply remove them and move on. Good airflow around the lower stems reduces humidity and helps prevent any fungal issues that might otherwise follow.

Fungal Root Rot

In persistently wet conditions, Pythium and Fusarium root rots can set in. As well as yellowing leaves you will notice stems becoming soft and brown near soil level. There is no cure once rot is advanced. Remove and destroy affected plants. For the remaining plants, drench the soil with a copper-based fungicide, improve drainage, and reduce watering frequency. Avoid replanting marigolds in the same spot next season.

Nitrogen Deficiency in Late Summer

In containers that have not been fed for several months, nitrogen leaches away with each watering. The result is a general pallor and yellowing that starts on older leaves and progresses upward. Apply a balanced liquid feed every two weeks from midsummer onward. Do not over-correct with high-nitrogen feeds, as too much will suppress flowering.