Tomato Growing Guide Contents

Stopping tomatoes

For cherry varieties (apart from Tumbler and other bush varieties) stop the plants (pinch out the growing points) in the first week of September; for all other types stop them in early August. It may help to ripen the remaining fruit if you remove some of the older leaves which are shading them. Don’t do this in very hot conditions as the excessive heat may make the fruit soft.

Picking tomatoes

With cherry varieties you should pick your first ripe tomatoes when they are flowering on the 6th truss; for larger-fruited types you’ll have to wait until the 9th truss flowers. You might get a new truss approximately every ten days, so if you plant in mid May with the first truss in flower, you might expect your first pick sometime in the first half of July for cherry tomatoes and about a month later for larger varieties. In the meantime, buy British-grown tomatoes for the best flavour.

Sowing tomatoes

Sow about 25% more seeds than you want plants, to allow for some losses and so you can select the strongest seedlings. You will need some clean seed trays. Those with individual cells work well, but you can also use suitable food packaging if you make sure there are holes for drainage. The trays need to be at least 3cm deep. Fill them with good quality seed compost – look out for Gardening Which Best Buys (and Don’t Buys!) Make sure the surface is level and firm. Sow the seeds about 3cm apart and cover with about 4mm of compost. Water them using a watering can with a fine rose. Cover with clear plastic or a sheet of glass. Put them somewhere warm to germinate: 20 – 25°C is ideal. After about 5 – 7 days the seeds will have started to germinate. They must be uncovered immediately and put somewhere with plenty of light, but still ideally 20°C (minimum 16°C). It may be necessary to spray the seedlings with a fine mist to help the emerging seedlings shed their seed coats.

Soil or grow bags for growing tomatoes?

Getting the watering right in a grow bag or pot is always more difficult than if you grow tomatoes in soil. If you have a small greenhouse and always grow your tomatoes in the same place, then there can be a build up of soil-borne diseases such as Fusarium (wilt; crown and root rot), Verticillium wilt and Corky root rot. You can get round this either by not growing in the soil or by using grafted plants: see To graft or not graft for tomato growing?

What does determinate and indeterminate mean?

Tomato varieties can be divided into three groups according to their growth habit: ‘indeterminate’, ‘semi-determinate’ and ‘determinate’.

Indeterminates (also known as cordon varieties) provide a continuous harvest from about mid-June (cherries) or early July (others) until first frost. This type produces side-shoots, which must be removed, and needs to be ‘stopped’ (have the growing point pinched out) in the first week of September for cherry tomatoes or early August for other varieties. In a commercial greenhouse, each tomato plant produces over 30 trusses and grows for up to 50 weeks (including propagation). The stems grow up to 15m long. All of our varieties apart from Lizzano and Tumbler are indeterminate.

Semi-determinates are in between and do not need side-shooting or stopping; Lizzano is a semi-determinate variety suitable for growing in patio containers or hanging baskets; it may need staking if grown in open ground.

Determinates are short and bushy (they are also known as bush varieties). They grow to about 90cm (3ft) tall and usually don’t require support. Determinates provide lots of ripe tomatoes at once and are suitable for growing in containers. They do not require ‘stopping’. Tumbler is a determinate variety.

Nutritional disorders of tomatoes

Iron deficiency

Symptoms are yellowing of the very youngest leaves at the top of the plant, with even the smallest veins remaining green; usually caused by over-watering and/or poor soil aeration. It can be treated by spraying with a proprietary iron foliar feed, but you also need to fix the underlying cause.

Magnesium deficiency

Symptoms are yellowing of the older leaves with the main veins staying green. This can be due to a number of causes:

  • Low soil magnesium levels (especially if potassium level is high)
  • Root problems caused by waterlogging, disease, over-application of soluble fertilizers
  • Stress due to heavy fruit load

Removing the underlying cause should alleviate symptoms. Use a liquid feed which contains magnesium as well as potassium. Have your soil analysed and apply magnesium fertilizer before the next crop (if required). If it’s really bad you can spray with 1 litre per 10 sq m of a 2% solution of Epsom’s salts, with a little washing-up liquid as a wetter. Be careful, as this can scorch the leaves if done in sunny conditions.

Blotchy ripening & leaf curling

Blotchy ripening

Uneven ripening and fruit that tastes ‘flabby’ (low acidity) is usually due insufficient potassium. Feed every watering with a high potash tomato feed. Have your soil analysed and apply high potash fertilizer before the next crop (if required).

Leaf curling

Early in the season, there can be large differences in temperature between the warm, sunny days and cold nights. These wide diurnal fluctuations can cause the leaves to roll up or curl. This is due to large amounts of carbohydrates accumulating in the leaves because the nights are too cold for the plants to assimilate them. It is usually a temporary problem that cures itself as the nights get warmer.