Why Is My Rosemary Changing Color?

Are the whole leaves of your rosemary turning yellow or brown?

Did the lower leaves turned yellow, and the overall growth has slowed down?

Are there any small insects on the plant?

Are the leaves only stippled with yellow?

Did some leaves turned reddish-brown or purple?

Do the leaves have a powdery white coating on them?

The lower leaves start to turn yellow and overall growth slows down in rosemary plants that are under fertilized or rootbound. Bump the plant out of its pot and check the roots. If they are dense and have been circling around and around the inside of the pot, it's time to either clip them back and return the plant to its original pot, or trim them and repot it in a larger container with fresh soil mix.

The small insects are whiteflies. These tiny, mothlike flies and their larvae feed by sucking plant juices. Whiteflies secrete honeydew, a sugary substance that makes leaves sticky to the touch. A minor infestation of these insects will not harm a mature, otherwise healthy rosemary but young plants weaken, and their leaves turn yellow and die. Spray infested plants with insecticidal soap every 3 days for 2 weeks.

Rosemary roots in soil that is constantly moist or soggy, will suffocate, causing its foliage to turn brown and die. Check the soil in the container. If it is too wet, stop watering immediately. Allow the rootball to dry out and trim off the dead stems.

Spider mites are known to cause yellow stippled leaves. You can control spider mites by spraying plants thoroughly with water 2-3 times a day for several days. For severe infestations, spray rosemary with insecticidal soap.

Reddish-brown or purple leaves on rosemary usually indicate sunburn. When moving rosemary from partial shade conditions to the full sun you need to do it gradually to avoid sun damage. Prune of damaged leaves and the rest of the plant will recover given you provide it with good care.

If the leaves have a powdery white coating on them, the cause is a fungal disease Powdery mildew. Powdery mildew usually appears in damp places. Thin your plants to ensure good airflow. Water rosemary from bellow to keep foliage dry. Any affected leaves should be cut off and removed.

Nutrient deficiencies are known to cause yellow leaves in rosemary. If the problem starts on young leaves and spreads to the old ones, it's likely an iron deficiency. If the first leaves to turn yellow are the oldest ones, it could be nitrogen, zinc, or manganese that's missing. Use a basic water-soluble fertilizer such as 20-20-20 with micronutrients to alleviate symptoms.