There are a couple of ways for approaching tomato growing in a greenhouse, you can either dig and prepare the soil of the greenhouse ready to accept the tomato plants or you can grow the plants in a container such as a plant pot (12″ diameter) or growbag.

Realistically most growbags that are available which can be 35 or 40 litres in size are only enough to support two plants. There are ways in which you can push this out to 3 plants but for the cost of a growbag its probably as well just to stick to 2 plants, particularly if you take good care of them and produce lots of fruit.

If you go for pots then you should steralise them before use, to do this you can use a dilute solution of a suitable disinfectant, something like Jeyes fluid is perfect for this task.

While we are on this subject, you really should wipe down the inside of your greenhouse with disinfectant as well to ensure any residual contaminants that could also cause disease are removed from the glass.

One of the reasons I am suggesting using large pots or growbags for growing tomato plants is because the soil in the greenhouse is going to need to be dug out and replaced every 2 or 3 years anyway to ensure that you get rid of any build up of disease and also because the soil will be pretty much spent in terms of nutrients.

Space is limited in a greenhouse so the best option for plant varieties is to use the indeterminate variety of tomato plant i.e. a vine plant. You can prune the plant to the required size, leaving about 4 to 6 trusses on the main stem, which is about 6′ to 7′ in height, greenhouse size allowing. This will give you lots of fruit over an extended period.  You will have to pinch out the main stem when you have enough trusses to stop further growth.

As an aside, using the bush variety is less convenient for greenhouses because they, as the name suggests, form a determinant size of bush without pruning which is probably a little too large in diameter for the average greenhouse. The fruit also has a tendency to all come at once.

Irrespective of the growing method you choose, you should start to feed the tomatoes at the first sign of fruit and for the duration of the growing period, twice a week should be sufficient. Also as you are in a greenhouse regular and consistent watering is also very important and I recommend 2 to 3 times a day with water that has been allowed to warm in the greenhouse.

As the end of the season nears a way of helping the last remaining fruit ripen is to hang a couple of bananas in the apex of the greenhouse. If that fails to ripen the last bit of fruit you can always use the green tomatoes for making a delicious chutney.

One of the main reasons for using a greenhouse when growing tomatoes is because of the climate you live in. If you cannot guarantee warm sunny weather for your tomatoes then you will need to consider using a greenhouse, this will help you control the climate for the tomato plants and give them a better chance of producing lots of edible fruit.

Clearly planting tomatoes in a greenhouse leaves you with limited options, for most people the greenhouse will be relatively small and probably only a little taller than the height of an average man, unless of course you have the space and money for a large more industrial sized greenhouse, but for the purposes of this article I am going to discuss the smaller option that is, I believe, more prolific in the home gardening environment.

This makes it much more difficult to use the tomato plant hanging option for your plants and in practical terms the only real option you have is to plant using the soil inside the greenhouse or to sit pots on the floor of the greenhouse, either way make sure you have a good mix of mulch, compost and fertilizer.

You will still need to be able to support the fronds of the tomato plant and with limited space a good way of doing this is to knock 3 stakes into the ground at each end of the planned run and to tie gardening string between the stakes. When the plants grow they pass through the strings and then hang over them a little like clothes on a washing line.

If you are inside a greenhouse the plants will be totally dependent on you for their water so you have a choice, invest in a self watering system or use hand watering. If you choose hand watering it is also good practice to leave the water in the greenhouse with the plants to allow it to warm a little before use. Takes a bit of discipline but as long as you refill after watering then leave overnight, that should do the trick and you will not shock the plants with cold water.

The final thing you need to take care of is not letting the greenhouse get too hot and or humid, if it is really sunny for a period you can paint the glass with a whitewash to reflect the sun away and you can open the roof light or door to let some of the heat get away but don’t forget to shut them again at night when it is cool.

Other than these few peculiarities the tomatoes should be treated in much the same as they would be if they were being grown outside, so in addition to proper soil preparation and watering, you need to take steps to keep them disease free, pest free and to give them access to plenty of nutrients via a feeding program.