Yellow leaves on tomato plants usually mean the plant is not getting enough nitrogen, or the soil is staying too wet
Tomato plants turn yellow for a few specific reasons, and most of them are fixable once you know what to look for. The yellowing starts at the bottom of the plant and works its way up when nitrogen is low — the plant pulls nitrogen from older leaves to feed new growth. If the whole plant yellows at once, or if the leaves look waterlogged and soft, the problem is usually overwatering or poor drainage. Less often, yellow leaves signal a disease or pest damage, but those come with other visible signs.
The good news is that you can usually tell which problem you have just by looking at the plant and feeling the soil. Once you know the cause, the fix is straightforward.
Key Takeaways
- Nitrogen deficiency causes yellowing that starts at the bottom leaves and moves upward, and it is fixed by feeding the plant with a balanced fertilizer or compost.
- Overwatering and poor drainage cause yellowing across the whole plant and soft, waterlogged stems — the fix is to let the soil dry out between waterings and improve drainage.
- Check the soil moisture by pushing your finger two inches into the ground; tomato soil should feel damp but not soggy.
- Yellow leaves with brown spots or rings may signal disease, and you should remove those leaves and improve air circulation around the plant.
- Once you fix the underlying problem, yellow leaves do not turn green again, but new growth will be healthy.
Nitrogen deficiency: the most common cause
Tomato plants need a lot of nitrogen to grow, and when the soil runs low, the plant cannibalizes its own older leaves to feed new ones. You will see the bottom leaves turn yellow first — sometimes just the edges, sometimes the whole leaf — while the top of the plant stays green. This is natural and normal if it is only happening to a few leaves at a time, but if it is spreading fast, the plant needs feeding.
The fix is to give the plant nitrogen. You can use a balanced fertilizer (something like 10-10-10 or 5-10-5, where the first number is nitrogen), or you can add compost or aged manure around the base of the plant. If you are using a liquid fertilizer, follow the label directions for how much to use and how often. If you are using compost, work an inch or two into the top of the soil around the plant, being careful not to bury the stem.
Tomato plants in containers run out of nitrogen faster than plants in the ground, because water drains through the soil and carries nutrients away. If your tomato is in a pot, you may need to fertilize every two to three weeks during the growing season.
Overwatering and waterlogged soil
Tomato roots need oxygen as much as they need water. When the soil stays wet all the time, the roots cannot breathe and they start to rot. The plant responds by yellowing — sometimes the whole plant at once, sometimes in patches. The soil will feel soggy when you push your finger into it, and the stems may feel soft or mushy near the base.
The fix is to let the soil dry out between waterings. Tomato plants need about one to two inches of water per week, but that does not mean watering a little bit every day. Instead, water deeply once or twice a week and then let the soil dry out before you water again. Push your finger two inches into the soil; if it feels damp, wait another day or two before watering. If it feels dry, water until the soil is moist all the way through.
If your tomato is in a container, make sure the pot has drainage holes in the bottom. If water sits in the pot after you water, the soil is not draining fast enough. You can improve drainage by mixing perlite or coarse sand into the potting soil, or by repotting the plant into a container with larger or more drainage holes.
Poor air circulation and fungal disease
Yellow leaves with brown or tan spots, or leaves that look like they have rings or halos on them, usually mean a fungal disease. The most common ones on tomatoes are early blight (brown spots with concentric rings) and septoria leaf spot (small brown spots with dark borders). These diseases spread when leaves stay wet for too long, especially if the air around the plant is still and humid.
Remove the yellow or spotted leaves as soon as you see them — cut them off with clean scissors or pruners, and throw them in the trash, not the compost. Do not let them sit on the ground or on other plants. Then improve air circulation by spacing plants farther apart, pruning lower branches so air can flow under the plant, and watering at the base of the plant instead of overhead. Water in the morning so any water that does land on the leaves dries quickly.
If the disease is spreading fast, you can spray the plant with a fungicide made for tomatoes. Sulfur and copper are common active ingredients in organic fungicides. Follow the label directions for how often to spray and when to stop spraying before harvest.
Pests that cause yellowing
Spider mites and whiteflies can cause yellowing by sucking juice from the leaves. With spider mites, you will see tiny yellow or white spots on the leaves, and if you look closely at the undersides, you may see fine webbing. With whiteflies, you will see tiny white insects on the undersides of the leaves, and the leaves will be sticky (that is whitefly droppings). Both pests thrive in hot, dry conditions.
Spray the plant with water from the hose to knock off the pests, and repeat every few days. If that does not work, you can spray with insecticidal soap or neem oil, following the label directions. Make sure to spray the undersides of the leaves where the pests hide. Improve air circulation and avoid letting the soil dry out completely, because dry conditions make these pests worse.
When to remove yellow leaves
Once a leaf turns yellow, it will not turn green again. You can remove it to help the plant focus its energy on new growth, or you can leave it on the plant if it is not bothering you. If the leaf is diseased (spotted or discolored in a pattern), remove it right away so the disease does not spread. If the leaf is just old and yellow from nitrogen deficiency, you can leave it until it falls off on its own.
When you remove leaves, use clean scissors or pruners and cut the leaf off at the stem. Do not tear it off by hand, because that can damage the plant. If you are removing diseased leaves, wipe your tools with rubbing alcohol or a 10 percent bleach solution between cuts so you do not spread the disease to other parts of the plant.
Preventing yellow leaves going forward
The best way to avoid yellow leaves is to start with good soil. Tomato soil should be rich in organic matter — mix in compost or aged manure before you plant. If you are planting in a container, use a potting mix that is made for vegetables, not garden soil, because garden soil compacts in pots and drains poorly.
Water consistently and deeply, and let the soil dry out between waterings. Mulch around the base of the plant with two to three inches of compost or straw to help the soil hold moisture evenly and to keep it from splashing onto the leaves. Space plants at least two feet apart so air can flow around them. If you are growing tomatoes in a humid climate, prune the lower branches to improve air circulation under the plant.
Frequently Asked Questions
Can I eat tomatoes from a plant with yellow leaves?
Yes. Yellow leaves do not make the fruit unsafe to eat. The fruit will be fine as long as the plant is otherwise healthy. If the yellowing is from disease, the fruit itself is still safe, but you should remove the diseased leaves to stop the disease from spreading.
How long does it take for a tomato plant to recover after you fix the problem?
New growth will be green and healthy within a week or two of fixing the problem, but the yellow leaves that are already on the plant will not turn green. You can remove them to make the plant look better, or leave them until they fall off on their own.
Should I fertilize my tomato plant every week?
No. Most tomato plants in good soil need fertilizing every two to three weeks during the growing season. If you fertilize too often, you can end up with lots of leaves and few tomatoes. Follow the label directions on your fertilizer and adjust based on how the plant looks.
What if only the edges of the leaves are yellow?
Yellow edges usually mean the plant needs potassium, or the soil is too salty (from tap water or old fertilizer buildup). Flush the soil by watering deeply and letting water drain out the bottom of the pot, then feed with a balanced fertilizer. If you are using tap water with high chlorine or salt, try using rainwater or letting tap water sit overnight before watering.
Can yellow leaves spread to other plants?
If the yellowing is from disease, yes — fungal spores can spread to nearby plants through water splash or on your hands and tools. If it is from nitrogen deficiency or overwatering, it will not spread, but other plants in the same soil may develop the same problem if the soil conditions are the same.