Growing fresh herbs all through the winter is one of the easiest and most satisfying ways to use a greenhouse. Clumps of chives, mint and marjoram and parsley plants can be potted up and brought inside to continue growing. Basil, which needs lots of heat and is very tender, will stay growing longer in a tunnel or glasshouse than outdoors before the cold kills it. Although bushy herbs such as rosemary and thyme are hardy outdoors all winter, potted plants under protection will produce mild, fresh-tasting young shoots long after outdoor plants have stopped growing.
Pot up herb plants or clumps in good soil or compost or a mixture of the two, water them well and leave them out of direct sun to recover for a few days. Then place them in good light in cool, airy and well-ventilated conditions. Basil is best sown in small to medium sized pots and kept warmer than the others. Water them regularly and don’t let them sit in saucers of water or dry out completely. Use water warmed by keeping it in the greenhouse for a few days to avoid chilling the plants. Feed them occasionally and remove any dead bits. If flower buds appear, pinch them out to keep them growing fresh leaves. Watch out for aphids and guard against slugs: both stay active in the warmth of greenhouses much later than outdoors. Be ready to cover plants with fleece, bubble-wrap, cloches or other protection on frosty nights.