Advice
RHS Help & Advice
Growing tomatoes successfully
Tomatoes are being
sold in an ever increasing range of colours, sizes and shapes
with the recent interest in heritage cultivars fuelling further
interest.
Sowing
Sow tomato seed in mid-March for outdoor crops, and mid-February for growing in an unheated glasshouse. Seed can be expensive, but usually only a few plants of any one cultivar are needed and germination is usually good.
A single 9cm (3 1/2in) pot or small seed tray should provide enough plants for most gardeners. Fill pots with seed or multipurpose compost, level, firm gently and water. Sow seeds on the compost surface, spacing them evenly, a finger-width apart, to reduce contamination from damping-off disease. Cover with a fine layer of vermiculite and keep at approximately 21°C/70°F, ideally in a heated propagator, although a clear plastic bag will do.
Seedlings emerge after about five days; place them in the best-possible light and at a temperature of around 18°C/65°F to prevent ‘legginess’. Leggy plants produce their first flowers high up the plant and require more staking or, in greenhouses, more training.
A heated glasshouse is by far the best environment, but fair results are possible using a sunny windowsill.
Pricking out
Seedlings in communal pots should be large enough to prick out into pots of multipurpose compost two weeks or so after sowing. Fill pots two days before pricking out, water well, and allow the compost to warm to room temperature to reduce damping off. Hold seedlings by their cotyledons (seed leaves) to avoid damage to the delicate stems. Water in lightly with tepid water. Reduce the temperature to 16ºC/60ºF when plants reach 15cm (6in) high.
Growing on
Ideally, grow on in a glasshouse (or failing this a well-lit windowsill), spacing plants so that their leaves never touch. Plants grown so close that leaves touch tend to be leggy. About a month after pricking out, the plants will be ready for planting into their final positions, this usually being indicated by the production of the first flower clusters or ‘trusses’. The stress of being grown in pots promotes flowers earlier than would form if the plants were in less stressful positions in soil, growing bags or other less restricted environments. Greenfly can be very damaging to tomato seedlings – treat as seen, ideally with systemic insecticides that will protect the plant from re-infestation.
Planting and training
Aim to plant outside in early June, in unheated greenhouses in mid-April, and in heated greenhouses in mid-February. Plant 40cm (16in) apart when the first flowers open, watering in well.
Bush types require no supports or shoot removal. Support cordon types with canes or string, carefully removing sideshoots as they develop. Stop cordon plants two leaves past the fourth (outside) or sixth (indoor) truss.
1. 
2.
Above: Cordon grown tomatoes. Plant the young tomato plant
next to a cane and tie in (1). Remove sideshoots (2) as they
develop. Photography copyright RHS
Watering and feeding
Roots should be kept moist but not waterlogged. Pots and grow-bags require the most frequent watering. Irregular watering can result in splitting and blossom-end rot, whereas over-watering can impair flavour. Feeding isn’t essential for soil-grown plants, but those in bags or pots benefit from regular feeding, using a formulated tomato feed and following manufacturer’s instructions.
Fruit set and harvest
Tomato flowers self-pollinate freely. However, indoor plants benefit from being gently shaken to dislodge the pollen. Misting flowers can also help fruit set.
Pick fruits as required, with the calyx still attached. Outdoor plants can be laid on straw and covered with cloches to speed up ripening.