Using greenhouses and cold frames to extend the growing season for vegetables and salad crops makes sense for those of us in the chillier parts of the world. You can start seedling plants which would otherwise struggle outdoors in early spring and you can carry on cropping from mature plants well into autumn. So what are the best ways of using greenhouses for home crops? |
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As with so many aspects of gardening, it rather depends upon what you want.
Most amateur gardeners have not the time and dedication to heat the greenhouse throughout the chilly months. Nevertheless the greenhouse can be a valuable asset at almost any time of the year.
Here are some ways of using greenhouses to extend the season, mainly for food crops, without additional heating.
Using greenhouses and cold frames to start off seedlings
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If you have no heating at all and you are in a temperate part of the world, you will probably need to use a heated propagator for starting off your seedlings. An unheated greenhouse will be too cold for early crops.
Later in the year (around April onwards for the UK,) seedlings will often thrive without extra heat. You need either a good bench or work surface (staging) in the greenhouse or alternatively a seed tray stand. The seedling trays should be kept off the floor as that is the coldest spot in the greenhouse.
Cold frames can also be used but you may need to supply some kind of heat until the frosty months are past. If you have a greenhouse and some unheated propagators this can be a part solution. Start seedlings inside the house in the propagators and move them outside when they are seedlings have germinated.
A double thermometer is a useful tool as it allows you to see the lowest temperature of the previous night. You can use this to help you judge when it is warm enough for any particular seedling to be put into the greenhouse. (The maximum temperature shown also helps you plan your greenhouse's ventilation.)
If you want a good guide to greenhouse or sunhouse growing, consider the Greenhouse Gardener's Companion 
for a good all round manual which covers just about everything - and it's quite humorous too!
Using greenhouses for growing on seedlings 
Many of the smaller vegetables can be given a good and early start by growing them on in the greenhouse. Beans , especially dwarf varieties can be grown in pots and tubs. Some, such as French dwarf beans can even be grown to maturity in the greenhouse.
Leeks and onions can be started in boxes of soil. Cabbage family seedlings can be given a good head start by keeping them inside the greenhouse for a few weeks.
All these plants will need to be hardened off gradually before they are put out into their permanent quarters.
Using greenhouses, picture right: salad crop seedlings can get a quick start in the greenhouse during spring or autumn
Using greenhouses for over-wintering crops Many small vegetables such as lettuce and mizuna can be ...
