If you are lucky enough to have a greenhouse, you are in the perfect position to get a head start when it comes to your garden. A greenhouse will also give you the opportunity to grow all-year round, keeping up a supply of vegetables during winter.
A productive vegetable plot relies on being able to grow tender young plants under glass, ready to plant out when the risk of frost has passed. Many plants will need to be hardened off before planting out, which involves placing them outside – ideally in a cold frame – for a week or so to enable them to get used to colder temperatures. Check the individual requirements for each type of crop you are growing, with timings also dependent upon where you live.
Sow seeds fortnightly in spring to ensure a steady supply through the summer and autumn. Tomatoes are probably the classic greenhouse crop and you can choose from so many varieties. Grow young seedlings in grow-bags, ready to go outside in warmer weather, and make sure your greenhouse is well ventilated to avoid mildew-type problems. If you are lucky enough to have a glut, you can make up big batches of tomato sauce and freeze them.
Lettuces are easy to grow under glass and there are so many different varieties from which to choose, ranging from iceberg to radicchio. Germinate the seeds in early spring and thin out once the seedlings have grown. These can be planted outside in early May and harvested when needed. Keep them well watered and keep an eye out for slugs. Young plants can also be picked earlier, especially leafy plants such as spinach that are much sweeter and milder when young.
Peppers are a great crop for greenhouses, as they need heat and sunshine and plenty of water. You can grow capsicum or bell peppers, or go for chillies if you like your food spicy. Harvest as and when you need them. Peppers are sweeter and chillies spicier when they have ripened, although they can be eaten when still green. Chilli plants can be kept indoors on a sunny windowsill, but water them daily.
Cucumbers can be grown outside from seed; however, most varieties need to at least be germinated under glass. If your greenhouse is heated, you can plant seeds in early spring; if it is not heated, wait until mid-spring. Cucumbers plants need supporting – a bamboo cane is perfect. They can be planted out in early summer but will benefit from being under a cold frame for a week to harden them off and acclimatise them to cooler temperatures.
Greenhouses are also great for growing tender flower plants and giving them a head start in the garden. Sweet peas grown in an unheated greenhouse are much more reliable than those planted directly in the garden. You can plant seeds in winter, keeping seedlings under glass over the winter, or in the spring. For spring-planted sweet peas, harden them off before planting out in April.