Here's a happy fella. He's feeling a bit smug because his carrots and potatoes are ready before anyone else's because....he's got a greenhouse!
Growing vegetables in a greenhouse allows you to grow crops that would be unpredictable or unsuccessful outdoors, particularly in colder regions. Tomatoes, peppers, chillis, cucumbers, melons are all obvious examples. But you can grow many different types of crops if your greenhouse is big enough, providing a vegetable harvest before they would be ready if grown outside, such as early potatoes or early carrots. You can also grow crops such as winter lettuce which need protection. Being able to sow and grow in a frost free environment, protected from the wind and elements is another obvious advantage of owning a greenhouse.
Your greenhouse can be sophisticated or as basic as you require. By heating the greenhouse all year round and using specialist grow lighting, you can create an artificial growing environment that will provide you with out of season crops during the winter, although you would need to artificially pollinate. Itís more likely that your greenhouse will be unheated or kept frost-free and used to bring crops on early or to start sowing early. Outdoor vegetable varieties can be started off in propagators in the greenhouse and then pricked out before being hardened off for outside planting, giving you a head start on outdoor sown crops.
In the winter, youíll need to line the inside of your greenhouse with bubble insulation to keep it insulated and have a basic greenhouse heater to keep it from dipping below a minimum temperature during particularly cold spells. Likewise, in the summer youíll need to provide shade from the direct sun through the use of shade mesh or a paint-on product such as Coolglass.
You will need to provide ventilation through the hotter months so it is worthwhile buying an Auto Vent which is thermostatically controlled to automatically open roof vents during warm weather. During the summer, it's important to damp-down in your greenhouse by watering the floor to create sufficient humidity to protect the plants from the worst ravages of the heat. Furthermore, greenhouse nasty Red Spider Mite loves dry hot greenhouses so there's another good reason to damp-down. Try not to water onto the plants' foliage in very hot conditions as this can scorch the leaves.
If you donít want to run to the expense of a greenhouse, you can buy polytunnels which recreate the same environment as a greenhouse. Alternatively, mini greenhouses or plastic walk-in greenhouses or growhouses or even simply coldframes can all be used for early sowings or protecting tender crops at fraction of the price of their larger counterpart.