5 common tomato problems and how to solve them

Tomatoes are the quintessential summer garden crop, but they’re not always simple to grow. In fact, by this point in the growing season, even the most experienced gardener may be having problems. According to experts, unusual weather, including a massive amount of rain in some places, is making for an especially tough tomato season this year. The good news: Most tomato plant issues are solvable.

“Don’t panic, whether it’s a pest or a disease,” says Doug Oster, a gardening writer and broadcaster in Pittsburgh. Even serious issues, he says, don’t necessarily spell doom. “Make sure you’re identifying the problem before you take action, and that will save you a lot of heartache in the garden. Don’t make a rash decision.”

Here are five common issues that can derail your fruit production, along with expert advice on how to deal with them.

Fungus

All of the rain this summer, on the heels of a cool spring, isn’t ideal for tomatoes. “They want Italian summer, not east coast spring,” Oster says. And while rain is important to growing vegetables, constant downpours have a big downside.

“There are fungal spores in the ground — they’re always going to be there — and when it rains, they splash up,” Oster says. “They get on the bottom leaves, and if the leaves stay wet for a long period of time, those fungal spores make their way into the plant’s system.”

Common fungal infections, like Septoria leaf spot and early blight, start to set in around this point in the season, Oster says. “The bottom leaves will start to turn brown and yellow, and it’ll work its way up the plant.”

While most fungal issues won’t kill the plant, he says, they will slow growth and production. The simplest way to combat a common fungus is to remove the infected foliage. To avoid spreading fungus, disinfect your pruners with a 10 percent bleach solution between plants, Oster says. Or if you’re using your hands, wash them after touching an infected plant.

There are also fungicides on the market that can help. Dave Freed, a California gardener known as “the Tomato Guy,” swears by sulfur dust, an organic preventative available at garden stores. “It stops it right in its tracks most of the time,” Freed says. He applies the dust using a bag made from pantyhose. “I just fill it up and shake it over the tomato plant so it falls lightly on the leaves,” he says, “and that will solve the problem if you do it every two or three weeks.”

Oster anticipates the wet weather will also cause a spike in rarer fungi, such as Anthracnose. “That’s a bad one,” he says. “Your tomatoes will start having black soft spots in them, and once the plant has it, there’s almost no way to get rid of it.”

And the pathogen Phytophthora infestans, also called late blight, while rare, is even worse. It “rears its ugly head maybe once a decade, and it’s disastrous,” Oster says, spreading from plant to plant, blackening stems, leaves and fruit.

But be careful not to confuse it with more typical, treatable diseases. “People looking at early blight and Septoria leaf spot think they have late blight and start pulling out their plants,” he says. “And I’m like ‘No, no, this is different.’” Circular brown spots that start on the lowest leaves indicate one of the less-threatening infections. “But if you start to see the stems of your plant and the tomatoes themselves turning black,” Oster says, “act fast.”

Mineral deficiency

Unusually frequent heavy rainfall also washes away nutrients, wreaking havoc on your soil quality, says Carrie Spoonemore, co-founder of the From Seed to Spoon app. When tomatoes can’t get enough calcium, specifically, they can develop blossom-end rot, where brown lesions form on the bottom of the tomato where the flower was attached.

Adding crushed up eggshells or Tums around the base of a plant can boost calcium. Sometimes, though, blossom end rot happens when the soil contains plenty of calcium, but the plants “don’t have the water they need to get the calcium up,” Oster says. That can happen because of inconsistent watering, like “when you have deluge thunderstorms, then let them dry out,” he says.

Take heart, though: Blossom-end rot isn’t a plant-killer. “If you catch it quick, you know there’s some kind of water issue, and you can correct that,” Oster says. “The number one thing you can do for tomatoes in the garden is a nice layer of mulch to try to keep the soil evenly moist.”

Hungry (and thirsty) plants

Tomato plant leaves should be a deep, vibrant green. If yours are looking pale, Oster says they may be due for a good meal. “Tomatoes are heavy feeders,” he explains. They eat up nutrients, especially once they begin to fruit, and pale foliage is a sign they need fertilizing. Feeding is especially important, Oster says, for plants being grown in pots. “Whatever container they’re in, they’re going to quickly eat up what’s in there,” he says. “You’re doing yourself quite a service by doing your fertilization, usually weekly at this point in the season.”

But Spoonemore cautions to not go overboard. “If you have too much nitrogen in the soil — and this goes for any plant, not just tomatoes — you’re going to have a lot of lush green leaves, but not a lot of flowering or fruiting.” Thankfully, overfeeding is a relatively easy problem to solve.

“If I apply too much nitrogen fertilizer, like fish oil or something like that, I just try to essentially wash the soil out,” Spoonemore says. She waters heavily, then adds a calcium-rich supplement (she favors Tomato-tone), “so I don’t get the blossom-end rot afterward.”

And as the summer wears on, Freed says, a regular watering schedule becomes critical. “When the really hot weather comes, the important thing is to keep the roots moist,” he says, to avoid premature ripening and grow the largest tomatoes possible. “If that tomato plant thinks it needs to go into survival mode, it’s going to tell all the fruit on there, no matter what size, ‘hurry up, turn red, we’ve got to go to seed, the end is near.’” Keeping the roots consistently moist can help the plant regulate its temperature, Freed says, which will yield larger, more flavorful tomatoes.

Insufficient support

Tomato plants get big — sometimes much bigger than gardeners expect — and by midsummer they may be getting a bit wild. Good structural support is important, Oster says, for a few reasons. If you keep your plant from flopping over and dragging its leaves on the ground, you’ll reduce its exposure to fungus. Plus, a trellis or other support can increase airflow and encourage more prolific fruiting.

For most heirlooms and indeterminate varieties (those that keep growing until the first frost), “the normal tomato cage is useless by this time of year,” Oster says. Many growers make their own, or use a large trellis built with a cattle panel, a section of fencing available at farming supply stores. But if you have a whole stack of the traditional round wire cages, you can still make it work, says Oster.

“I tell people to start with the biggest one of those cages you can, but then take another one, flip it upside down, and wire it to the top of the first one,” he says.

Big bugs

One of the most voracious tomato plant eaters is the caterpillar that metamorphoses into a five-spotted hawkmoth. To fuel the transition, these caterpillars, otherwise known as hornworms, have to eat a huge number of leaves. Tomatoes are their favorite.

“They are monsters,” Spoonemore says. “You go out one day and everything’s fine, then you go out the next and you’re like, ‘What happened to every leaf on this tomato plant?’ It happens so quickly.”

Hornworms aren’t tiny — they can grow to roughly the size of your index finger — but they do have the advantage of camouflage. “With how large they are, it’s amazing how well they blend in,” Spoonemore says. “They’re the exact color of a tomato plant stem.”

The best way to defend against hornworms is to pull them off the plants and relocate or squish them. They also make a great snack for a backyard chicken flock, or the frogs in your local pond. And while they can hide in plain sight, there’s a trick to spotting them. “If you go out in your garden at night, with a black light flashlight, they will glow fluorescent green and you’ll be able to find them,” Spoonemore says.

Ultimately, hornworms and most other tomato plant troubles are surmountable. If you give them everything they need, Oster says, tomatoes can outgrow most problems. His best advice: Don’t be discouraged by a tough season. There’s only so much you can control, after all, and there’s always next year.

“You get one of these seasons where it’s wet and humid, it’s just difficult,” he says. “As gardeners, we just have to accept the ebb and flow of what Mother Nature gives us. She’s always in charge.”