Plenty of vegetable and flower seeds can be sown in the UK in December. Some can be sown outside, direct in the ground, while others need to be sown in a heated propagator indoors. Young plants of some hardy varieties can be planted, too.
December is a good time to plant as it means you can get ahead before spring. Sowing vegetables and flowers early can result in earlier harvests – winter-sown broad beans are ready to harvest from May, while hardy annual flowers sown in December can flower several weeks sooner than those sown in spring. Sowing and planting in December can mean fewer empty beds and more roots holding the soil together, which can prevent a loss of soil nutrients and erosion in winter rains.
Sowing seed in December can mean you extend your season of harvest – by sowing now and then again in spring, you could potentially enjoy some crops and flowers for longer.
Shorter daylight hours can make it tricky to provide enough light for indoor seedlings. To counteract this, use a grow lamp. This will stop seedlings becoming leggy and help them grow stronger. What’s more, a heated propagator can increase the number of crops you can sow in December, such as chillies and aubergines.
Vegetables to sow in December
Sow broad beans in December for a crop as early as May. Sow direct outdoors if conditions are mild – broad bean seeds should germinate within a couple of weeks and will then stop growing and enter dormancy until temperatures pick up in the spring. In cold conditions or areas, sow into pre-warmed soil beneath cloches or fleece, or in multi-celled trays in a greenhouse or on a windowsill, which you can plant out later.
Boxing Day is the traditional day to sow onion seeds. Choose seeds, rather than sets, and start them off in pots indoors or undercover, to aid germination. Plant the young onion plants out in spring, spacing them 10cm apart.
In mild regions, you can plant garlic sets outdoors in well drained soil. If you have a heavy soil then start them off in a multi-celled tray, planting one clove per cell. Water well and keep in a greenhouse or similar until spring, and then plant them out 10-15cm apart.
Certain lettuce cultivars, such as ‘Winter Gem’, have been specially bred for their ability to grow at low temperatures and provide a harvest. Sow in pots in an unheated greenhouse or a cold frame, for the best results.
Lamb’s lettuce, also called corn salad, has been grown and eaten for centuries in the winter months. Simply sow the seeds in an unheated greenhouse, and enjoy the freshly picked leaves soon after.
Mustard greens can be sown in the greenhouse, or on the windowsill, and will crop throughout winter if temperatures remain mild (if they enter dormancy they will start growing again when temperatures increase). The young salad leaves can be used to pep up dishes like soups, salads and stir fries.
Microgreens are the seedlings of leafy herbs and plants that we would usually allow to grow to full size before harvesting. Sow and grow them indoors for a burst of flavour on dishes throughout winter.
Chillies and aubergines
Flowers to sow in December
Sweet peas can be sown indoors in December, ideally in containers, such as cardboard tubes, that can be planted into the soil, minimising root disturbance.
Laurentia are bushy, half-hardy annuals, with star-shaped, scented flowers. The seeds can be sown under glass in winter, in a bright spot. A heated propagator will help to warm the soil when sowing.
Geraniums are often propagated by taking cuttings, but why not try growing them from seed, too? Ideally, surface sow in a heated propagator, in a bright spot out of direct sunlight.
Hardy cyclamens like Cyclamen coum and Cyclamen hederifolium can be sown in December. Before sowing, soak the seeds overnight, then sow straight after in small pots. Keep the pots at a temperature of 13-16°C.
Though usually grown as annuals or biennials, snapdragons are actually short-lived perennials. They’re easy to grow, and can be sown under glass in December, to flower from June onwards.