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Growing your own tomatoes is satisfying on many levels. Their season is fast and high-yielding, making it an ideal crop for both a veteran green thumb and a novice gardener. But as you scan your tomato plants daily for new growth and flower buds (which will later become delicious fruit!), be on the lookout for common diseases and pests that can wreak havoc on your harvest.

We spoke to Alexandria Stubblefield of Plant California Alliance (a member-based association for professional and academic horticulturalists), for advice on how to ensure your crop reaches its full potential.

Below she offers her expertise on how to spot signs that your tomato plants need some extra TLC, what to do to save them from ruin, and how to keep them happy, healthy, and thriving.

Related Reading: Why Are Heirloom Tomatoes So Expensive & Are They Really Worth It?


One of the most important things to look out for, according to Stubblefield, is a fungus among your plants.

Blight is a common tomato terror that falls into two categories: early (which takes hold at the start of the season when the weather is warm and wet) and late (mid to late season as the weather cools).

“With early blight, you’ll notice that there are some black or brown spots on the fruit and/or on the leaves,” says Stubblefield. “With late blight, it might start out like little spots, but it will actually grow and you’ll start to see white fuzzy mold forming on the leaves and the fruits may start to turn brown.”

To prevent blight, keep the bottom leaves trimmed on your tomato plants to minimize the risk that they come in contact with any potential spores in the soil. Stubblefield also discourages overhead watering given that the leaves will get wet and provide a more welcoming environment for fungal growth.

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If your plants begin to show signs of  blight, immediately clip the infected leaves and fruit, do not compost, and disinfect your tools thoroughly.

For an all-purpose organic fungicide, Stubblefield relies on neem oil, a plant-based concentrate. Blend with water and spray early in the morning so that it soaks into the leaves and dries out before the midday heat.

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If you encountered blight this year but want to try your hand at growing tomatoes again next season, Stubblefield recommends starting over in a different section of your yard. In the afflicted area, consider rotating in a different crop that’s less susceptible to blight (avoid anything in the nightshade family, which, in addition to tomatoes, includes potatoes and peppers).

Finally, you could try to eliminate blight altogether between seasons via solarization. “Cover the soil with plastic and try to kill it off by creating an environment that’s too hot for the spores to live,” Stubblefield advises.

Related Reading: How to Start a Garden: 5 Tips for Beginners


Another common fungal contaminant is mildew, particularly of the powder variety. Instead of a fuzzy residue that results from blight you’ll notice your leaves have been dusted with spores. 

Allowing your plants to breathe is key to prevention. “Make sure that you’re pruning the canopy of your tomatoes as well so that there is some air flow getting in there,” Stubblefield advises. “It really is hot and humid inside the center of a tomato plant. They like that, but if it’s too dense of foliage, it can also make the plant more inviting to mildews and blight and other kinds of fungal issues.”

Blossom End Rot

If you notice that the bottom of your tomato fruits are starting to brown and develop a leathery texture, you’re dealing with blossom end rot.

The problem here is a lack of calcium. While most common commercial fertilizers rely on a combo of nitrogen, phosphorus, and potassium, they don’t often contain much calcium, which tomato plants crave.

Give your tomatoes a calcium boost by sprinkling the soil with powdered oyster shells or gypsum or use clean, dry eggshells from your kitchen, crushed as fine as possible.

Related Reading: How Eggshells and Coffee Grounds Can Make Your Garden Grow


While you’re waiting for those juicy tomatoes to grow, caterpillars don’t mind getting a head start on the green matter, feasting on the foliage as well as the fruit. “They can really wreak a lot of havoc,” Stubblefield says.

Clearing these butterflies-to-be out of your garden can be difficult considering their Darwinian camouflage coloring which blends in seamlessly with the stems and leaves.

Stubblefield recommends keeping the plants shielded while they’re young using a floating row cover to prevent these interlopers from showing up in the first place.

If caterpillars have already staked a claim on your plot, pick them off by hand when you spot them and use organic Bacillus thuringiensis (Bt) spray to take back your territory.

Related Reading: Get Rid of Garden Pests with These 6 Natural Deterrents 


You’ve waited weeks, maybe months for your tomatoes to ripen, but alas, the fruit has cracked, split, or burst open on the vine. 

According to Stubblefield, these frustrating results are likely a sign that you’ve been overwatering. When watering by hand with a hose or a can, set a recurring alarm on your smartphone. Be mindful of your timers with a drip irrigation system, monitor your garden on a daily basis, and scale back if you begin to see cracks.

Related Reading: How to Grow an Herb Garden, Indoors or Out


In short, Stubblefield’s general advice when it comes to growing tomatoes comes down to:

“Keep your plant well pruned. Have a consistent watering schedule. Make sure it gets the proper supplements that it needs throughout its growing season, like calcium. Fertilize on at least a monthly basis with a balanced fertilizer.” But she warns that even with all that in mind, it might not be enough to keep your tomatoes out of harm’s way. “No matter how good of a gardener you are,” Stubblefield says, “nature is always there.”

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Header image courtesy of Mint Images / Getty Images

David is a food and culture writer based in Los Angeles by way of New York City. His work has appeared in the Los Angeles Times, CBS Local, Mashable, and Gawker.
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