Growing tomatoes successfully depends on avoiding some common pitfalls that can trip you up along the way. Knowing what to expect and what to do about it will greatly improve your chances of a truly terrific crop of tomatoes. Read on to discover how to troubleshoot some of the most common tomato problems...
Common Tomato Pests
Aphids and whitefly
Aphids and whiteflies are regular visitors from early summer. They often congregate in large numbers, sucking sap from your plants and leaving their sticky excrement, known as ‘honeydew’, on the foliage. Some types also transmit plant diseases.
Small infestations can simply be blasted off with a jet of water. Or try spraying plants with a solution of soapy water, taking care to reach the undersides. To minimize potential problems attract pest predators such as ladybugs and hoverflies by planting flowers close by – marigolds are a good choice. You can even buy these predators to introduce into enclosed environments such as a greenhouse.
Spider mite
Warm, dry conditions are perfect for spider mite, which like aphids and whitefly can quickly weaken plants. Look out for their faint webbing. Peer closer and you may be able to see the tiny, usually red, mites.
Spider mites love drought-stressed plants, so don’t let your tomatoes dry out. If spider mites do attack, spray the foliage with a fine mist of water, ensuring you reach all parts of the plant. Then cover the plant with a row cover for a few days to create the shady, humid conditions that will repel the mites.
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Tomato hornworm parasitized by braconid wasp larvae
Tomato hornworm
Many parts of North America are prone to tomato hornworm, a caterpillar that chews holes into tomatoes. Check plants regularly for signs of damage and remove and destroy any caterpillars you find. Cocoons like those shown in the photo above are great news – they belong to braconid wasps, which feed on hornworms to bring them under control.
Tomato Diseases
Late blight
Late blight strikes during spells of warm, wet weather. Foliage and then the fruits become covered in brown blotches; eventually the plant simply wilts and collapses. Late blight also affects potatoes, which are related to tomatoes.
Blight is rare on indoor tomatoes, so grow plants under cover if it’s been a problem in the past. Avoid splashing the foliage when watering, and remove and destroy infected plants as soon as you spot the first signs of blight. You could also grow varieties described as ‘blight resistant’.
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Blossom end rot
Blossom end rot is a disease caused by dry soil conditions and a shortage of calcium. Fruits form sunken black patches at the blossom end of the fruit.
Ensure your tomatoes have enough water at all times, and feed them regularly with a liquid tomato fertilizer. This is the best way to guarantee your plants are getting all of the minerals and nutrients they need for healthy growth. Pay particular attention to plants in confined spaces, such as pots or growing bags.
Watering and Feeding
Split fruits
Irregular watering often leads to split fruits, when a sudden rush of water causes the fruits to swell quicker than the skins surrounding them. Instead of leaving soil to completely dry out between each watering, aim for consistent soil moisture. Water regularly and mulch tomatoes with plenty of organic matter to keep roots cool and moist.
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Mineral deficiency
Mineral deficiencies usually show up in the leaves first. Magnesium deficiency is the most common form and often arises as a result of high potassium levels. To correct the deficiency, spray a solution of Epsom salts directly onto the foliage then switch to a tomato feed that contains a higher proportion of magnesium.
Wilted plants
Plants can wilt when the soil is either too wet or too dry. Too wet and the roots literally drown, while very dry soil won’t supply plants with all the moisture they need.
Pay close attention to watering. Containers of tomatoes should have good-sized drainage holes at the base so that excess water can drain out. Raise containers up onto pot feet if water doesn’t drain away easily. In all cases, water generously when it’s dry, or set up an irrigation system if you can’t be there to water. Later on in the season mature plants with lots of foliage may need watering twice a day.
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Poor Fruit Set
Poor fruit set, when flowers fail to produce fruits, is a very common problem. A lack of bees, excess heat, poor nutrition, and very dry or humid air are all possible causes.
Make sure pollinating insects such as bees can reach plants growing in greenhouses and tunnels. Improve pollination by simply twanging or tapping on supports to dislodge the pollen, or gently twiddle the flowers between your fingers.
Provide as much ventilation as possible in hot weather. If your climate’s also very dry, raise the humidity around plants with regular watering. And make sure to feed your plants regularly with either an off-the-shelf tomato feed or a homemade high-potassium liquid fertilizer such as comfrey tea.
Don’t be put off by all these potential problems. So long as you know what you’re looking at and react quickly, your tomatoes are likely to recover. Please drop us a comment below to let us know about any other tomato problems you’ve encountered and how you got around them.
