How to Grow Tomatoes in Greenhouse or Grow House

by John Harrison

A growhouse is just a plastic mini-greenhouse with a zippered front that takes one growbag.

Greenhouse Tomatoes

Growbag Watering Pots

Planting Out Tomatoes

Once the young plants are outgrowing their 3½" (OK - 8.89 cm ) pots with the roots coming through the base, it is time to plant on the tomatoes.

For the Growbag

The standard growbag contains between 35ltr and 40 ltr of compost, which is not a lot to grow 3 good plants on. I use a tip I saw on Gardeners World and it works brilliantly.

On top of the growbag I place three 9" bottomless pots. You can buy these for ring culture or just cut the base off some old pots. Using them as a template and a sharp knife, I cut rings into the surface of the bag and 'screw' the pot into the compost below. At the same time, I cut some small slits in the side of the bag about ½ above the base to allow for drainage.

Next, I insert two growbag watering pots to facilitate watering the bag. These are really clever little devices that ensure water and feed gets into the bag. They are re-usable year after year and available from Harrod Horticulture

The also have a ring system that you just screw into the growbag with watering and feeding around the side - take a look here

Having prepared the growbag, I then deep plant the tomato into the pot, leaving just under an inch for watering. A bamboo cane goes in to tie the plant to, which is held in place by going through holes in the top of the growhouse.

You can see small whitish nodules or hairs on a tomato shoot just above soil level. These ‘pimples’ will grow into roots if they contact the soil, enabling the plant to take on more nutrients and moisture

A good watering then beds everything down.

For the Greenhouse

You can grow tomatoes in a bed down the side of a greenhouse but the soil will need to be changed after a couple of years at least or you will get a build up of disease and the the soil's micro-nutrients will be depleted no matter how much fertilizer you add.

This is more work than you might think and I prefer to grow in large pots using the spent compost as a soil conditioner at the end of the season in the home greenhouse but in the border of the allotment greenhouse as it holds water well if I miss a day.

By large, I mean 12" although you can get away with smaller. Pots are measured across the top, by the way. The different depths and styles mean that the professionals buy according to capacity but I just use my eyes!

Some broken crocks in the bottom to ensure drainage, fill with general purpose compost, plant deep and insert a cane to support the plant. Job Done.

In a full size greenhouse you can use strings from the roof anchored into the pot instead of a cane. I think this was more trouble than using a cane and more of a fiddle to tie the plant to.

Growing On - Cordon Tomatoes.

Tomato Sideshoot Removal
Pinching Out Tomato Side Shoot

Because of space limitations, I only grow cordon tomatoes under cover rather than the bush varieties, which take up more floor area. The name of the game is growing tomatoes, not foliage, but the tomato is naturally a bushy plant. Left to its own devices, it would spread along the ground, producing many side shoots, which would make more side shoots and so on. It would not make that many tomatoes as its energy would be going into growth.

Tomato Side Shoot Removal

To channel the plant's energy into producing fruit rather than foliage we need to remove the sideshoots These start in the angle between the leaf and stem. The earlier they are removed, the less energy is wasted. A job to be done at least once a week. After the plant is stopped, I have noticed it really goes mad for sideshoots - so watch out.

Be careful not to confuse these shoots with a truss. A truss is the stem that carries the flowers, which turn into tomatoes.

If you let a sideshoot grow to about 6" or more, you can cut it off, pop it into a pot of wet compost and have another plant. Useful if you find yourself short of plants and it is too late to start more from seed.

Stopping Tomatoes

When the plant has set four or five trusses it is time to stop it. You just take the leading (main) shoot at the top and cut it off. This means all the plant’s energy can be diverted into fruit, which will hopefully mature before the end of the season.

If you let the plant just carry on you will find yourself with a lot of tiny green tomatoes at the end of the year.

Feeding Your Tomatoes

When the first truss has set, which means the flowers have gone and you can see tomatoes beginning to form, it’s time to start feeding. Tomatoes are greedy, we want lots of juicy fruits, so you need a good tomato feed. I use either a bought organic feed, which is based on comfrey, Tomorite or make my own comfrey liquid feed.

Feed weekly at least to keep the plant going.

End of Season

As the season draws to a close, it becomes a race to ripen the crop prior to the frosts. To help this along I remove the lower leaves and expose the fruits to the sun. By this stage the plant does not need as much energy so the leaf removal will not affect it.

At the end of the season before the first frost, I harvest all the green tomatoes of reasonable size and these can either be ripened or used in chutney etc.

You can also hang up the vines with fruit on in a frost-free, cool dark place and they will slowly ripen. If kept in a draw with a ripe banana they will ripen quickly due to the gas given off by the banana

Growhouse Tomatoes

Click on the photo to view larger image

The Tomato Grow House

Here you can see the young plants sitting in the pots, which gives them far more compost to take nutrients up from. As it is early in the season, the top shelves are in place and being utilised for various tender seedlings

Later, these will be removed and the plants will be tied to the crossbars which are part of the grow house structure.

Tomato House

The Tomato Grow House

Here we are in early August and the plants have filled the shelter and been stopped. The pots are hidden under the mass of marigolds which keep whitefly at bay and make for a more attractive item in the garden.

In front our emergency lettuce in a trough (useful when I forget my allotment shopping order) and our cat, Aphy, is watching a butterfly off-shot with great interest.

Unfortunately, we had just picked the ripe tomatoes before taking this photograph but you can see the green ones on the plant.

Tomatoe grow house

Further Information: Tomato Growing Guides



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