Yellow oregano leaves are usually a sign that the plant is lacking nitrogen or specifical minerals such as iron. A general all purpose fertilizer like fish emulsion or pelted chicken manure can help to solve low nitrogen levels. Apply iron chelates if you notice green veins and yellow leaves.
Yellow leaves can also be repaired if the plant is given the nutrients it needs. I have given my oregano an all purpose fertilizer and it repaired the leaf color after 2 weeks. I use pelleted chicken manure but any organic all-purpose fertilizer will work well.
This article will explore why oregano leaves turn yellow and what you can do to save it.
Why oregano leaves turn yellow and easy solutions
Here are the top reasons why oregano leaves turn yellow and what you can do to solve each one.
Lack of nitrogen
Nitrogen is essential for oregano to for green leaves. Chlorophyll is the bright green pigment that exists in the leaves responsible for allowing the plant to photosynthesize and create its own energy. Oregano plants that lack nitrogen will have lower levels of chlorophyll and the leaves can turn yellow.
Yellow oregano leaves caused by a lack of nitrogen can be solved is easily solved by giving them a feed of diluted liquid nitrogen fertilizer every 2 weeks over Spring. Add a few handfuls of pelleted chicken manure around the plant for longer lasting nitrogen and your plants will replace old yellow leaves with new green leaves.
To prevent yellow leaves on oregano due to the lack of nitrogen dig through some aged cow or chicken manure through the soil before planting. Give the plant pelleted chicken manure in spring and fall and you will not have any problems.
Lack of minerals
If your leaves have turned yellow but the veins have remained green this can indicate a mineral deficiency. It is likely that this is relating to the Fe or iron chelates. Try a dose mixed in water or add some slow release fertilizer that contains iron.
Not enough sun
Oregano plants that are not getting enough sunlight can develop yellow leaves. Oregano plants grow best in full sun and if they are getting too much shade they will lack the green color in their leaves.
To solve this problem move potted oregano plants into a bright sunny area in late spring and summer. This will avoid any early spring frosts that can damage leaves and give the plant more sun. Oregano plants are a summer growing herb so bright sunlight is important to keep them growing throughout the year.
Overwatering can cause nitrogen and minerals to be washed out of the soil and cause oregano leaves to turn yellow.
Oregano plants prefer to dry out between watering rather than grow in consistently wet soil. Avoid overwatering oregano plants by checking the soil moisture before adding more. Move the soil with your finger or a spade to see if it is damp.
Water the oregano if it is dry 1-2 inches below the surface. Adding bark mulch will help to regulate the amount of water that the oregano gets as it can absorb extra water and slowly release it to the plant.
Overwatering is more likely to happen to oregano planted in pots. If your pot sits in a pot tray or self-watering pot take care not to leave any water sitting in the bottom. Excess water can cause the roots to rot and stop the plant from absorbing nutrients.
To avoid this always tip out excess water from the catch tray after watering.
Pest attack can be the cause of yellow or damaged leaves on oregano plants. Sap sucking insects such as aphids or spidermite can damage the plant.
Small green aphids can attack oregano plants sucking their sap and causing leaves to turn yellow. These insects will attack new growth and can appear in Spring. Ladybugs can help to control aphid populations but if not you will have to take action.
I always like to treat this pest problem by trimming off the affected leaves and spraying down the plant with water. Use neem oil on the plants to treat the pests and wait for 2 weeks before eating the leaves.
Underwatering can cause oregano leaves to turn yellow. Poor, sandy soils that drain quickly can dry out quickly and cause the roots to suffer, the plant to dry out and cause leaf damage.
To avoid this problem start by planting the oregano plant into improved soil. Always improve the soil in your garden beds before planting out new oregano plants. Use aged cow manure and compost and mix it through well.
Water oregano every 3 day in the heat of summer. Apply a 2 inch layer of bark mulch in the warmer months and this will help to keep water in the soil for longer and prevent the plant drying out.
What to do when oregano leaves turn yellow
Here are the top 3 steps to follow if your oregano leaves turn yellow.
1. Check the soil and water it well
Stick your finger 1-2 inches below the surface of the soil to check the moisture level. Water oregano every 3 days, 2-3 times. If the soil is still wet wait until the top layer has dried before watering again.
2. Liquid feed with nitrogen fertilizer
Add dilute liquid fertilizer to the oregano plant to give it a nitrogen boost. Do this if the leaves look yellow and you should see an improvement in 2 weeks. Follow this up with some longer lasting nutrients using a slow release fertilizer.
3. Trim the oregano
Trimming off up to 1/2 of the oregano stems can help it to recover from yellow leaves. This will encourage the plant to send up new shoots, grow new leaves and recover quickly.
Following these steps will help a yellowing oregano plant to return to healthy growth.
Yellow leaves on Oregano | Summary
Oregano leaves can turn yellow due to a lack of sunlight, lack of nitrogen, mineral deficiency, over or underwatering or pest attack. To avoid this problem plant them into good quality soil improved with aged animal manures, mulch with bark mulch, and give them a slow release all-purpose fertilizer in spring and fall.
Oregano are a hardy herb that can recover quickly when the problem is identified and solved. Happy growing.
I am an accredited practicing dietitian, experienced gardener and a dedicated cook. I love writing and sharing my experience so you can learn from my successes and mistakes.