Why Are My Plant Leaves Turning Yellow? 7 Common Causes

You walk into your grow space and notice it: one of your healthy green leaves has started turning yellow.

Should you add nutrients? Water more? Water less? Change the light?

Yellowing leaves are one of the most common warning signs growers encounter, but they can have several different causes. Before adding another product to your feeding routine, take a closer look at where the yellowing started and how the plant is behaving.

Here are seven common causes and what you can do about them.

1. Overwatering

Overwatering is often caused by watering too frequently rather than applying too much water at once. Constantly wet growing media can reduce the oxygen available to the roots, making it harder for the plant to absorb water and nutrients.

Possible signs include:

• Yellow, soft or drooping leaves
• Growing medium that remains wet for a long time
• Slow growth
• An unpleasant smell around the root zone

Allow the growing medium to dry sufficiently between waterings and make sure your container has adequate drainage.

2. Underwatering

A thirsty plant can also develop yellow leaves. The leaves may feel dry, thin or crispy and the growing medium may pull away from the sides of the container.

Water the plant thoroughly and check that the entire root zone receives moisture. Avoid giving frequent little splashes that only wet the surface.

3. Incorrect pH

A plant may have nutrients available in its growing medium but still be unable to absorb them effectively when the pH is unsuitable. This is sometimes called nutrient lockout.

Use a reliable pH meter to test your water or nutrient solution. Remember that the ideal range can differ depending on the plant and whether it is being grown in soil, coco or a hydroponic system.

4. Nutrient Deficiency

The position and pattern of the yellowing can offer useful clues.

Uniform yellowing that begins on older, lower leaves may indicate a nitrogen deficiency. Newer leaves turning yellow while their veins remain green can be associated with iron availability.

Avoid immediately increasing every nutrient. First check your watering, pH and root health, then make one measured adjustment at a time.

5. Too Much Nutrient

More food does not always mean faster growth. Excess fertiliser can cause salt accumulation around the roots, leading to yellowing, burnt leaf tips or brown edges.

Always follow the recommended dosage for your nutrient product. If you suspect overfeeding, check the strength of your nutrient solution and consider flushing the growing medium with correctly balanced water.

6. Light or Heat Stress

Leaves closest to a powerful grow light may become pale, yellow or dry. Excess heat can also cause curling, wilting and rapid moisture loss.

Check the recommended hanging height for your light and monitor the temperature around the top of the plant—not only at floor level. If the plant appears stressed, increase the distance from the light or improve airflow.

7. Pests or Root Problems

Mites and other sap-feeding pests may cause yellow speckles, patches or weakening foliage. Inspect the undersides of leaves and the points where leaves join the stem.

Unhealthy roots can also prevent a plant from taking up water and nutrients. Healthy roots are generally firm and light in colour, while damaged roots may appear dark, soft or slimy.

A Quick Checklist

Before changing your feeding programme, ask:

• Is the growing medium too wet or too dry?
• Does the container drain properly?
• Is the pH suitable for the growing method?
• Did the yellowing begin on old leaves or new leaves?
• Are there burnt tips, spots, webbing or visible pests?
• Has the lighting, temperature or feeding routine recently changed?

Yellow leaves are a symptom rather than a diagnosis. Observe the whole plant, make one adjustment at a time and give it enough time to respond.

Need help identifying what your plant is telling you? Visit GeneSage Boutique in Newton Park, Gqeberha, or browse our growing media, nutrients and essential grow accessories online. We’ll help you find a practical solution for your setup.