How to Grow Tomatoes in Your Greenhouse

In the past, gardeners have tended to be rather conservative in their choice of tomato varieties. But modern hybrids, developed for commercial growers, have been joined in recent years by a huge number of heritage varieties from all over the world. These include varieties with green, white, brown, orange, yellow and striped fruits as well as the conventional red. They can be anything from currant-sized to giant beefsteaks.



If you are prepared to provide some background heat in the greenhouse later in the spring, start sowing now. Plants will be ready to plant out about eight weeks from sowing.


All seeds sown usually germinate, and as seed of modern hybrids can be very expensive, decide how many plants you want and sow just enough. Surplus seed can be saved and should remain viable for up to five years if stored somewhere cool and dry. An airtight jar containing a bag of silica gel, and kept in the fridge, is ideal.

Scatter the seed thinly into a small pot containing moist multipurpose compost and cover with another 1cm of compost. Place the pot in a propagator set to a minimum of 15°C, but preferably nearer 21°C. Germination takes 7-10 days; less at the higher temperature. If you do not have a propagator, cover the pot with polythene or cling film and put it in a warm place until the seedlings appear. Move them somewhere warm and light, e.g. a sunny windowsill.

When the seedlings are large enough to handle, carefully separate them, holding the tip of the seed leaf, not the stem. Pot them individually into 7- or 8-cm pots. Water and keep at 18°C for a couple of days, then lower the temperature to 15°C to produce short, stocky plants.


Three or four weeks after pricking out, pot the plants into 10-cm pots. If the plants are tall and leggy, remove the lower leaves and plant them as deep as the new pot will allow. This will not harm the plant – in fact, the buried stem will quickly produce roots. Very leggy plants can be rescued by coiling the stem and burying it.

Gradually harden off the young plants. In a propagator, open the air vents progressively, then remove the top altogether. Finally, move them on to the greenhouse bench, providing background heat at night if necessary.


Plant into the open greenhouse. If you have soil borders, this is the best place to grow tomato plants. But do not grow tomatoes continuously in the same border because soil diseases gradually build up. Alternate tomatoes with non-related crops (e.g. cucumbers) each season. Work plenty of organic matter into the soil before planting to provide nutrients and retain moisture.

If you do not have borders, or have had poor results, use large pots filled with multipurpose compost or the contents of growing bags, rather than planting in the growing bags themselves. Gardening Which7 trials have shown that it is easier to keep tomato plants watered if they are in pots rather than growing bags.

Plant one plant to a 10-litre pot or three plants to a standard growing bag. Using 15-litre pots or two plants to a growing bag will make watering easier in high summer.

Most greenhouse tomato varieties are tall plants with a main shoot that grows upwards for several metres. The best way to control them is to support the main stem and remove the side shoots. Tomato plants grown in this way are said to be grown as cordons. To grow as cordons, bury a length of soft string under the tomato plant and attach the other end to the greenhouse frame. Or, better still, grow each plant next to a garden cane tied to the top of the greenhouse. Allow about 45cm between plants.


Tie the main stem loosely to the support as it grows. Pinch out any side shoots that form but take care not to damage the tiny clusters of yellow flowers.


Pick the fruit when it is fully ripe and has developed its full color. Water the plants frequently, which may mean twice a day in growing bags or pots on the warmest days. A trickle irrigation system will automate the process if you are not able to attend to the plants twice a day.

Feed plants regularly with tomato food, and ventilate the greenhouse on sunny days, by opening the door.


Stop the plant in early September, by pinching out the growing tip of the lead shoot. This stops further trusses of fruit developing and allows the trusses already formed to ripen. Keep pinching out side shoots, and remove dead or yellowing leaves. Banana skins in the greenhouse will encourage ripening of green fruit.


Pick unripe fruit, clear the plants and clean the greenhouse.

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About the Author: Greenery always attracts Arthur Kunkle. He has a big garden where he plants many fruits and vegetables. His passion for gardening motivates him to write and share different tips on gardening.

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