Sow flowers in the greenhouse during autumn

The climate changes, and it is getting warmer. This we especially see in autumn and winter. Winter is typically more grey and wet than clear and cold. The average temperature is higher which means that you can use the greenhouse all year. Although during winter the greenhouse is used differently than in the summer. In autumn and winter, you can pre-germinate flowers and get your flowers to bloom early in June.

Previously, it was only possible in England, and places with a similar climate, to sow flowers in autumn so you can get early flowers the following year. But now this can also be done in for example Denmark and Germany due to climate changes.

What are hardy annuals?

Hardy annuals are a specific group of summer flowers that can be sown in autumn. ‘Annual’ means that they grow and produce seed for then to die in the course of a single season. They are categorised as ‘hardy’ meaning they as young plants can survive the winter if they are in the greenhouse.

When to sow in autumn?

It is important to sow at the right time. This is when the plants have started germinating and are growing, but before they have grown too big and have started blooming. A rule of thumb is to sow around autumnal equinox since the growth of the plants rely on the length of the days. In 2022 the autumnal equinox is on 23^rd of September. To sow just before this date and right after is usually fine.

What flowers can be sown in autumn?

Here at Spirekassen we recommend the following flowers for autumn:

Cornflower, Centaurea cyanus
Love-in-a-Mist, Nigella damascena
Larkspur, Delphinium consolida
Queen Anne’s lace, Ammi majus
Khella, Ammi visnaga
White laceflower, Orlaya grandiflora
Greater quaking-grass, Briza maxima
Hound’s-ear, Bupleurum rotundifolium
Wild carrot, Daucus carota
Snapdragon (although there’s a risk that the flower stem won’t be as long when cultivated in autumn)

How to cultivate hardy annuals in the greenhouse

Last year I made a couple of rookie mistakes when sowing hardy annuals in the greenhouse. I was sowing the seeds too close to each other – I cannot recommend this. I got too many plants, and they did not have enough space during winter. I had to transplants them which could have been avoided.

Sow when it is autumnal equinox (23 September 2022)
Get a seed tray with cells
Fill the tray with soil
Irrigate so the soil is soaked
Make a hole a few millimetres deep
Sow 1-2 seed(s) in each cell
Lightly cover with soil or vermiculite

Keep the seed tray moist, and within a few weeks they will start to germinate. For flowers such as Queen Anne’s lace, wild carrot and khella, it may take longer to germinate. In the next few months, your hardy annuals will get about 5 cm tall. Soon it will be cold, and the plant growth will come to a standstill.

Please avoid that the seed tray is not too wet during winter in the greenhouse. If it is a very cold winter, it is a good idea to use a crop cover cloth.

Springtime

The plants in the greenhouse will be hardened during winter, and in mid-April they can be moved to your cut flower garden. Even though your plants are hardy plants, it is a good idea to harden your plants a couple of days before they are permanently moved outdoor. Move the plants outside a few hours a day and bring them back in the greenhouse at night. After 3-4 days, you can transplant the flowers. Consider using a crop cover cloth during the night. It does not matter if it is frost.

Why you should sow flowers in Autumn

Sowing flowers in Autumn is a shortcut to early flowers in the flower garden. Usually, it can be difficult to find flowers for bouquets in the end of May. From tulips and other flower bulbs are done blooming to summer flowers start to appear, there are not many flowers to pick. If you sow in Autumn, you can pick flowers as early as in June.