What’s wrong with my plant? Trying to figure that out can be challenging. Here are a few common issues you might run into, their causes and ways to correct the problem.
Germination and the early growth stages:
These issues can happen when you first plant seeds inside, maturing seedlings and young plants that have been transplanted into the garden.
| Symptom | Possible Cause | Less Obvious Cure Options |
| Poor germination | Old seed | |
| Improper soil temperature | ||
| soil dried out after seed coat started to swell | ||
| Seeds planted too deep | ||
| Not enough contact between soil and seed | ||
| Stem rotted at soil line | Damping-off disease | *see below |
| Leaf curl | Too much fertilizer | Flush soil with fresh water or transplant seedling |
| Yellow lower leaves | Not enough light | |
| Magnesium deficiency | Add a little epson salt to water (1T/gal) | |
| Leggy growth | Not enough light | |
| Air temp too warm | ||
| Pale leaf color | Nitrogen deficiency | |
| Low pH | ||
| Bronze leaf edges | potassium deficiency | |
| Over watered | ||
| Discolored roots | Excess salts | Flush soil with fresh water |
| Poor root growth | Compact soil | Transplant seedling into lighter soil mix |
| Phosphorus deficiency | ||
| Mold on soil | Soil too wet | Transplant seedling into lighter mix |
| Low pH | Add a little baking soda to water (1T/gal) |
*In the seedling stage, the most common problem for tomato plants when they are started inside is a disease called ‘damping off’. The seedling stem will look like it is pinched-off or rotted at the soil line. Unfortunately, there really isn’t anything you can do to save a seedling infected with damping-off, but it’s important to keep the disease from spreading to your other seedlings. Damping-off can be caused by a number of different pathogens, but it reproduces in the soil and can spread through the air. One reason I recommend planting tomatoes in separate soil cells (rather than an open flat) is to isolate any potential problems if they occur. Remove the diseased plant, and try treating the remaining seedlings. Using a drench of mild chamomile tea or sprinkling the soil lightly with ground cinnamon will often do the trick. It’s important to not replant the soil cell that had a diseased plant. Doing everything you can to prevent the disease in the first place is even better. Use clean seed starting trays. If you use the same ones year after year, make sure you wash them thoroughly and allow them to dry. Some people use a mild solution of bleach and dry them in the sun. Watering from the bottom, having good air circulation (oscillating fan), using a heat mat to make sure the soil is warm when the seeds are germinating (over 68°) and cooler after they are up and growing (below 77°), and using fine milled sphagnum moss as a top dressing on the soil can all help prevent the disease from ever showing up. Overcrowding can also lead to rapid spread of damping-off disease. Plant only one seed per soil cell.
As the Plant Grows:
There are any number of reasons why your tomato plant might not look the way you expect. Learning to recognize if it is time to panic or is it just nature following the life cycle of the plant, can save you a lot of headaches. Most healthy plants will grow faster than a disease and still produce plenty of fruit. But there are a few that can be a real problem and others can be corrected easily. Cornel has a great disease key online with lots of photos. If you see an issue that concerns you, check out their site https://blogs.cornell.edu/livegpath/gallery
There are also environmental issues that can look like a disease. Although these environmental factors must be corrected for the plant to fully recover, giving them a foliar spray of liquid kelp can help them deal with the stress.
- Wilting leaves can be a sign that the soil is too dry, but it can also signal that the soil has been too wet for a long time and the roots are rotting. Or that some creature has been chewing on the stem or the roots.
- Leaves on the upper part of a newly transplanted tomato plant can turn pale and golden, developing white patches that look like paper. This often happens if plant wasn’t ‘hardened-off’- slowly acclimating to direct exposure to the sun. These leaves have been sun burned.
- Leaves rolling in on themselves can mean the plant is under stress caused by hot dry weather, following a heavy pruning or a rapid growth spurt.
- Lots of flower buds dropping off or not forming into small fruits can result from just a few days of very hot dry temperatures. This can happen at any time during the season.
- At the end of the season, tomato plants are supposed to look bad. The lower leaves will yellow and drop off. At this time, they are putting all their energy into ripening fruit rather than sustaining the plant.
On the Fruit Itself:
Most often once a fruit has been damaged or shows signs of disease, there is nothing that can be done about fixing that individual fruit, but you can address the problem so it doesn’t affect the rest of your harvest. First, remove any unhealthy fruit as soon as you find it. If it’s just physical damage, you can often use the undamaged portion. Don’t throw them in the compost pile. They can attract pests and harbor diseases.
- Split skin. This occurs when the fruit starts to swell faster than the skin can stretch and is caused by inconsistent watering. Sometimes there is no way to control this when Mother Nature supplies a week of rain when the fruits are enlarging. This can be regulated (but not prevented completely) by using soaker hoses on a timer and mulching the plants which helps prevent large fluctuations in moisture.
- Large white patches on the skin. This is another form of ‘sun burn’ called sun scald. This happens when the fruit doesn’t have enough leaf cover to protect it. Aggressive pruning or leaf loss due to insect damage is the culprit. Some varieties have sparce leaf cover to start with and shouldn’t be pruned at all.
- Blossom-end rot looks just like it sounds. The blossom-end (the bottom) of the fruit develops a small dimple which continues to grow and rot the fruit. This is caused by lack of calcium in the fruit, which doesn’t necessarily mean that the soil lacks calcium (a soil test will determine if any amendment is needed). It does mean the plant was unable to absorb enough calcium AND supply it to the fruit when the fruit was developing. If the soil is too dry, too high in nitrogen or too low a pH can also affect the plant’s ability to absorb the nutrients it needs. Remove the damaged fruit as soon as you find it; it will not ‘heal over’ but continue to rot deeper. Consistency in watering (a soaker hose with a timer) and applying a mulch will help as will a pH of around 6.5. There are calcium sprays which claim to help this problem but the skin of the fruit cannot absorb the spray and suppling the plant with a foliar application can’t get the calcium to the fruit during the crucial time.
- Catfacing is a large area that is malformed and scared at the bottom of the fruit. This can be caused by cold night temperatures during the time when the plant is forming fruit. Often those plants planted too early for the region will have their first fruits develop this due to incomplete pollination. Later fruit sets, when the nights have warmed, don’t develop this problem as often. Catfacing is much more common in varieties that produce very large fruits. As with other physical deformities of the fruit, pick them as soon as you find them and use whatever parts are still good.
- Pithy, watery fruit. This happens often if the plant is watered too heavily shortly before picking the fruit. Whenever possible, slow down watering a week before a large harvest. If it rained before you planned to harvest, harvest as soon as possible after the rain, even if the fruits are green. Some varieties are more prone to this than others.
White ‘core’. This forms on the inside of a tomato and unnoticed until you cut into the fruit. Some varieties are more prone to white core; many older hybrids and heirlooms. Even the best tomatoes can develop a white core in part of the fruit if the temperatures fluctuate between very high day time temperatures (above 80°) and low night time temperatures (below 60°) when the fruit was enlarging. The best part is the rest of the tomato is tasty!
Then there is this PEST!
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Hornworms are fairly common. The tomato hornworm (note the black ‘horn’) and the tobacco hornworm (note the red horn) will both decimate a tomato plant in just a few days, eating every part of a leaf except the ribs.
Even though they can easily grow 4” long, most often you will not see him until you notice the damage he has done. He can blend in so well, they are hard to find, unless you look for their poop. He will be on the leaves directly above. Remove him and feed him to the birds or frogs.
If he has white Q-tip looking cocoons hanging off his body, he’s no longer a threat to your plant. Those are the eggs of the tiny Braconid wasp (a good guy), and the caterpillar is now the host food for those immature wasps. If you allow the wasps to finish their life cycle and hatch, they will help control any future tomato horn worms in your garden and they don’t sting people.