Common problems and disease when growing tomatoes

Unfortunately, there are quite a lot of problems and diseases which can attack tomatoes.

Curling leaves caused by low night temperatures ideally the temperature should not fall below 15C, although this is aesthetic only.

Yellowing leaves can be a magnesium deficiency which can be corrected by feeding with proprietary tomato food. If it persists despite feeding, it can be too little or too much water.  

Problems with split fruit - literally the fruit splits caused by irregular watering. Given our variable weather, regular watering is far from easy.

Greenback where the top of the fruit does not ripen fully caused by lower temperatures or lack of regular feeding.

Blight is the most serious and common problem and is often prevalent in a wet summer by which the plants develop brown patches and keel over the killer disease; you can spray them with proprietary sprays available from the garden centre but be quick off the mark, it can be too late by the time you spot the blight. If you don't want to spray, remove all infected leaves and dispose of not in the compost bin. Tomato plants grown in the greenhouse are much less susceptible to blight. If you grow tomatoes in an area prone to blight, ( the wetter parts of the country)  it may be better to grow in a greenhouse or lean to.  Blight is shown in the image below left.

Halo Blight, which is small spots on the fruit surrounded by lighter rings and is a water-borne fungal disease. To minimise the risk avoid splashing the fruit when you water. See How to grow tomatoes section on watering.

Blossom end rot: unsightly black patches on the underside of the tomato fruit. Caused by irregular watering, and more common in container-grown tomatoes than outdoors.

Botrytis, grey mould, which can also be a problem. To avoid this ensure as much ventilation as possible. Do not crowd the plants and open all vents and doors in the greenhouse.

Many types of tomatoes need support and this is usually done by staking. The image below right shows how the wrong type of support can cause problems. Here the stem has folded over the support and is close to snapping. 

Tomato plant with Blight

Blight on tomatoes

Heavy fruit causing stem to snap

Tomato with broken stem

What causes a lack of tomatoes and a small crop?

Tomato flowers becoming fruits on the vine

The flowers on tomatoes are very important because they become the fruit, i.e the tomatoes, so the more flowers the more tomatoes.  I show this in the image left, where the spent flowers have become baby green tomatoes with some yellow flowers at the end of the branch, which will also become fruits.

Poor pollination can cause a lack of tomatoes. The flowers need to be pollinated to produce the tomatoes, and this is more of a problem for tomatoes grown indoors in greenhouses and poly tunnels. Outside, nature does this by pollinating insects, such as bees. It is important to open greenhouse doors, windows and vents to let the bees in to do their work. Commercial growers with large poly tunnels and glass houses will import bees to pollinate. I have seen commercial growers in Iceland growing tomatoes in the depths of winter, utilising the thermal underground heat, and importing boxes of bees to fly around and pollinate.  

A lack of fruit can also occur during poor a summer if it is persistently wet and cold. The pollinators cannot fly around as much because of the adverse weather conditions. 

Top Tips for Growing Tomatoes

  1. Regular watering is really crucial: do not let the plants dry out.
  2. For best results feed regularly as soon as the first flowers appear.
  3. Keep an eye on the plants, thin out leaves and take off side shoots.
  4. Don't give up on them: Tomatoes will crop in a greenhouse until November, after which cut the vines and leave somewhere warm to ripen.
  5. To avoid diseases, if growing under glass, make sure there is good ventilation and air circulation, and avoid splashing the leaves when watering.

Step by step guide to growing tomatoes

Follow the Sunday gardener's step-by-step advice about growing tomatoes to ensure you have a successful sweet tasty crop every harvest. 

  1. How to grow tomatoes
  2. How to grow tomatoes from seed and what to do about weedy seedlings
  3. What are the easiest tomatoes to grow? Cordon or Bush?
  4. How to pot on tomatoes, dos and don'ts,  and why it is important.
  5. Hardening off tomatoes for growing outside
  6. Pinching out Side Shoots on tomatoes
  7. Stopping off  Tomatoes
  8. The Best way to Water and Feed Tomatoes
  9. How to ripen Green Tomatoes
  10. If you have found these tips helpful, why not buy the book: Success with Tomatoes The Sunday Gardener's guide to growing tomatoes, packed full of practical tips and helpful images, everything you need to know to grow a tasty crop. Only £6.20
Disease tomatoes