The beauty of growing tomatoes in greenhouses is that you have a longer growing season because you are not dependent on the weather.
There are a number of methods to grow great tomatoes in a greenhouse.
Growing Tomatoes in Greenhouse Soil
The most obvious is to plant and grow the tomatoes directly in the soil. This method is likely to give you the best tomatoes. It is also a little less work because the soil will retain more water than the other methods. It tends not work out as well after the first year because it presents a few problems. It doesn't take very long for your greenhouse to have pests and diseases. To help fight this, you can sterilize the soil each year by heating it, or just add new topsoil each year.
Here, are the steps for growing tomatoes directly in the soil.
You want to start each growing season with fresh topsoil and compost.
If you are planting seeds, plant them ¼ inch deep and plant roughly eight seeds to an inch.
For seedlings, dig a hole in soil that will allow you to plant the seedling deeper than it is in its pot. Alternatively you can dig a shallow trench and lay the plant on it side and bury it. Don't worry the plant will grow towards the sun. You want to bury it up to the top leaves. The reason for this is tomato plants develop roots along the stem.
Tomato plants need lots of sunlight so if they aren't going to get it from the sun put some florescent lights a few inches above the plants.
Make sure you water the plants regularly. Plants can develop blossom rot if you do not keep them moist.
Once the plants start to mature, you should give them some support in the form of wire cages or bamboo sticks.
Growing Tomatoes Using Grow Bags in a Greenhouse
One popular method is planting the tomatoes into grow bags or bags of soil, placed around the greenhouse. If you are using grow bags made for growing tomatoes, you just add your soil or compost and plant the tomatoes in it. If you are using bags of soil, it is best to get large bags. These are typically around three feet by one foot. Poke a dozen or so holes in the bottom for drainage. In the top, cut two to three Xs with a knife. Fold the flaps back from the Xs to form an open square, and either plant a seedling in each hole or plant two to three seeds in each hole.
Once the tomato plants start to mature you will need to provide some support. Grow bags that you buy can be reused each year, and bags of soil can be replace each year. This helps get around the big problem of pets and disease you would get if you planted directly in the soil. Growing tomatoes this way requires more attention to watering. You want make sure the soil is kept wet to avoid blossom rot, but you do not want to over water because you can drown the plants. If you are going grow your tomatoes this way, you should take a look at How to grow tomatoes in bags.
