7 plants to sow in December – discover flowers, vegetables, and herbs you can sow indoors this month

December is a time of cold, with frosts and snow for many of us, and the idea of sowing seeds may be far removed from any gardener’s plans. There are still gardening jobs to do throughout the winter, however, and that can include sowing selection of seeds - albeit a small one. 

If you do intend on sowing seeds in December, you will need to do it indoors and germinate seeds in a heated greenhouse or inside the house. The likes of a heated propagator or heated mat will often be beneficial in providing vital warmth to help germinate the seeds.

Sowing seeds in December helps you to get ahead and you will reap the benefit of earlier blooms and crops come the warmer months, along with enjoying a longer flowering season. 

In truth, the gardening year truly never ends, it may be cold outside but there are also things you can plant in December out in your backyard.

What can you sow in December?

The options for seeds to sow in December are minimal, thanks to the low temperatures and light levels of winter. However, there are still seeds you can sow sow for a flower bed or vegetable garden, and we take a closer look at seven potential ideas to add to your winter to-do list.

1. Geraniums

Tender geraniums, or pelargoniums, can be sown indoors from late December onwards to provide early displays of color. It means that these hugely attractive plants, that come in a plethora of colors and can have glorious scented foliage, can be flowering as early as April onwards from a sowing in December. Deadhead your geraniums regularly and you can then keep them blooming all summer long. 

The seeds are best sown in free-draining seed compost in trays or pots and germinated at temperatures of 70-75°F. Keep a close eye on your trays and make sure to keep the soil consistently moist, but not waterlogged, and do not let it dry out during the early stages of germination. 

These tender plants can be potted up and then moved outside after the risk of frost has passed. They will then need to be moved indoors again when the temperatures drop, to overwinter geraniums. A great example of a geranium to add a pop of color to any flower bed or pot is the Geranium Border Mix available at Burpee.

2. Laurentia

Laurentia are half-hardy annuals, they are usually grown as annuals in colder climates but can be hardy in US hardiness zones 7-10. These delicate and compact plants have soft green foliage and lots of small star-shaped flowers. Laurentia are popular in flower beds and borders, as well as for filling gaps in container gardens. 

Sowing these heat-loving plants in December will require additional heat, courtesy of a propagator or heating mat, as they also ideally want temperatures of at least 70°F. 

The bonus of an early sowing, providing you can give the seeds the heat they want to germinate, is that your Laurentia will flower from early summer onwards and provide blooms and color all the way through until the frosts arrive.

3. Snapdragons

Snapdragons, or antirrhinums, are a classic cottage garden plant and another popular flower which can be sowed indoors in December to flower early in the summer. Winter sowing can mean that your snapdragons start flowering from June onwards. 

There are many snapdragon varieties to choose from and they are plants that do need a long period of growing before bursting into bloom. You could choose a mix, such as the Snapdragon Liberty Classic Series Mix from True Leaf Market, to get a range of different colors for your beds or borders.

Sow the snapdragon seeds on the surface of quality seed compost. Do not cover the seed with a thin layer of soil, simply leave them on the surface and place the tray or pots in a propagator. Alternatively, put the tray in a clear plastic bag until the seeds have germinated. The ideal temperature for germination is around 68-75°F. Prick seedlings into individual pots and then grow them until you transplant seedlings out after the risk of frost has passed.

4. Sweet Peas

If you want to grow sweet peas, the seeds can be sown anywhere from fall through to spring - but a sowing in December is reputed to offer benefits to the plants. Sweet peas sown in winter will need the protection of a greenhouse or be germinated on a windowsill, but a winter sowing is thought to help to produce sturdy plants, with both solid top growth and strong roots. 

Sow your sweet peas in deep pots or root trainers, available at Amazon, filled with a good seed compost and plant each seed around an inch deep in the soil. 

Keep the pots moist, but not waterlogged as excess moisture can cause problems for sweet pea seedlings. Also keep a close eye on your plants as it is well known that mice do love to eat sweet pea seeds. 

5. Eggplant

They might be heat-loving plants and a typical summer crop, but eggplants have a long growing season and the benefit of sowing them early means an earlier crop. As eggplants can take six months to go from sowing seeds to harvest time, the earlier you can start the better. Though this will only be possible in certain situations. For example, if you are growing them as part of your greenhouse planning, or live in a warmer climate, then you will be able to plant eggplants into their final position earlier - this makes a December sowing ideal for the earliest pickings of ripe eggplants. 

Eggplant seeds will need lots of warmth to get them going as they like temperatures of 60-70°F for good germination. It would be an eggplant growing mistake to not give them supplemental heat to start them off. Sow them in individual pots or modules and keep the soil warm and moist. 

You can see the range of eggplant seeds available at Burpee

6. Onions

Onions can be sown from seeds or sets, and there is an old adage that the best time to sow onion seeds is on Boxing Day. Starting the onion seeds in mid-winter means they can have a long growing season and are ready to be planted out as soon as the soil starts to warm come spring. 

When growing onions from seeds, they should be sown lightly into modules and want temperatures of 50-60°F to germinate. Thin the seedlings that appear and keep the soil moist, before transplanting the onion seedlings into the vegetable garden after a period of hardening off in the spring.

7. Mint

Mint can be sown throughout the year and a sowing of this herb in December can mean you have a crop of mint indoors to harvest throughout spring. There are several herbs that can be sown indoors in winter, not only can you have indoor herbs to harvest but the plants can then be transplanted out into the garden come late spring. As well as growing mint, you could sow dill, chives, or basil in a windowsill propagator in December. 

You can get a wide variety of mint seeds, coming in many different flavors, and all are simple to sow. Scatter the seeds thinly on the top of moist compost and do not cover them. They want a good level of light and temperatures of around 60°F - artificial grow lights can be used to supplement the natural light. 

The seedlings should grow quickly and you can start to harvest mint as soon as the leaves reach a usable size. Picking the herb will ensure the plant keeps producing more of the most flavorful young shoots. The plants can be potted up into containers to grow outside once the risk of frosts has passed, or can be planted into a herb garden - but make sure to contain mint as the plant can spread quickly.

See the range of mint seeds available at True Leaf Market

FAQs

A specially-formulated compost for starting seeds is always going to be the best soil to start seeds in. Multi-purpose compost can also be used, but do not be tempted to use old garden soil to sow seeds into as it will sit far too wet over the winter months.