By Vanessa Richins
When I went into work today, my friend greeted me with the question:
“Why are my tomato plant’s leaves yellow?”
If only there was a simple answer to this. There are many different factors that can cause tomato plants to develop yellow leaves.
Here are some of the most common reasons:
- Under-watering: When plants don’t get enough water, they start to wilt and lose color. Under-watered plants are also more prone to attack from diseases and pests.
- Over-watering: On the flip side, overwatering can also cause yellow leaves. Over-watering can also cause root rots.
- Aphids: If you see sticky honeydew and small green, black, or red insects, you have aphids. A strong spray of water can knock these off. Ladybugs love to eat aphids.
- Nitrogen: Another cause of yellow leaves could be a lack of nitrogen. Test your soil with a basic kit available at home improvement stores or nurseries, or you can send in your soil for more detailed testing through your local cooperative extension. The cost varies by location but for example, it costs $15 here in Utah. If this is the case, add compost or a nitrogen fertilizer.
- Tomato Hornworm: If you see chewed yellow leaves, you may have tomato hornworms. Check the plant for these large, fat green worms. The easiest remedy is to just pick them off.
- Iron: Another nutrient deficiency signaled by yellow leaves is lack of iron. Add an iron chelate to the soil or the leaves, depending on the form.
These are only some of the causes. Other possibilities include: Early blight, psyllids, sunburn, curly top virus, whiteflies, flea beetles, and Septoria Leaf Spot.
If you are unsure of the cause, you can call a fellow gardener, ask here on Tomato Casual, or consult your local extension office.