Growing Herbs in Your Greenhouse

Herbs have a long history of cultivation, principally for their various culinary, medicinal and cosmetic properties. Today, whether grown for cooking or simply for their wonderful scents, herbs still have a special place in the garden and although they are more commonly planted outdoors, growing them in a greenhouse provides one or two opportunities which might otherwise be missed.

An Extended Growing Season

One of the most obvious benefits of having herbs under glass is the longer growing season that they can enjoy, even in an unheated greenhouse. Although herbs tend to be harvested during the spring and summer months, they can be made available almost year-round. Sow chervil (Anthriscus cerefolium), coriander (Coriandrum sativum) and parsley (Petroselinum crispum) in the late summer or early autumn and in the frost-free environment of the greenhouse, they will grow throughout the winter. Herbaceous perennial herbs such as chives (Allium schoenoprasum), tarragon (Artemisia dracunculus) and the many varieties of mint (Mentha) which normally die back during the colder months can also be forced in the greenhouse for winter use. Lift and divide mature plants in late summer and then replant them in a good quality, loam-rich potting compost. With a little routine care, they will keep putting out new shoots, which can be harvested as required to provide fresh leaves in the depths of winter. When spring comes, the forced plants can either be discarded or planted out – though it is important to leave them un-picked for a year or two to allow them to recover their natural vigour.

Over-Wintering

Even if you don’t plan on harvesting your herbs throughout the winter months, a whole range of herbs will benefit from being potted up and brought into the greenhouse while the weather is cold. Once their leaves drop, swathing them in bubble wrap to protect both roots and shoots will give them the best chance of getting off to a flying start once the new growing season gets underway. Tender and half-hardy herbs in particular, such as aniseed (Pimpinella anisum), cumin (Cuminum cyminum) and lemon verbena (Aloysia triphyllia) will also benefit from being brought into the greenhouse as the days get shorter.

Some gardeners also like to plant herbs in containers and bring them on over the winter – often in a heated greenhouse – to get an early start as the soil begins to warm up in the spring. If you do try this approach it is important to gradually harden them off with a spell in a cold frame before planting them out in their final positions to give them a chance to become fully acclimatised to their new conditions.

Sowing and Propagation

The greenhouse also makes an ideal place to propagate herbs, providing one of the quickest – and certainly least expensive – ways to grow a large number of new plants. Annual and biennials are typically raised from seed and it is a relatively simple matter to collect your own; perennials are more usually propagated by cuttings. Herb seeds should be sown in a good quality, specialist seed compost and once they have grown big enough to handle they should be pricked out and then transplanted into individual pots to be grown on. Both seedlings and cuttings will once again need to be fully hardened off before being planted out.

For most gardeners there are few things which match the satisfaction of knowing that you have brought on your own plants and the herb enthusiast is no exception. Whether you choose to propagate new specimens, enjoy a year-round crop or simply help tender varieties survive the winter, growing herbs in your greenhouse has an appeal all of its own.