Sowing Biennials: Start Foxglove Now for Next Year

There is that one plant that suddenly stands a metre and a half tall by the fence in June, dangling pink bells into the half shade, and that you are quite sure you never planted. Foxglove is a quiet self-seeder like that. And that is exactly the little secret of biennial plants: they need two summers but ask for almost no work. If you sow now in high summer, they flower next year without you having to juggle seed trays in spring.

What „biennial" actually means

Botanists sort plants by lifespan. Annuals germinate, flower and die in one season, like nasturtium. Perennials return for many years. Biennials sit in between: they live two growing seasons.

In the first year not much spectacular happens above ground. The plant forms only a flat leaf rosette and stores energy in root and leaves. Only the cold stimulus of winter unlocks the flowering rhythm, this is called vernalisation. In the second year the flower stalk then shoots up, the plant flowers, sets seed and dies afterwards. Classics of this group, alongside foxglove, are mullein, honesty, sweet william and hollyhock.

For you as a gardener this means above all one thing: you have to think ahead. What goes into the soil this summer is a promise to the next.

Why high summer is the right time

Timing is half the battle. Sow too late, say in September, and the plant goes into winter as a tiny seedling, freezes easily or is too weak to flower in spring. Sow very early in spring under glass and some species already flower in the first year, but then fall out of rhythm.

The window from mid-June to mid-July, that is CW 24 to 28, hits the middle exactly. The soil is warm, germination is quick, and the plant still has a good three months to build an over-wintering rosette before the first frost.

It is also practical that your seed bed usually frees up in high summer. Where radishes or the first lettuce stood, there is room for the next generation of flowering plants.

Sowing foxglove: step by step

Foxglove is the most rewarding beginner plant for summer sowing. The seeds are as tiny as dust, yet germinate willingly. You can sow directly into the bed or raise plants in pots and prick them out later. Raising in pots gives you more control over the site.

1. Prepare the seed tray

   Fill a shallow tray or pots with lean, fine seed compost. Too much nutrient encourages soft, rot-prone seedlings. Press the surface lightly and water it through beforehand so the fine seeds do not float away later.

2. Only press the seeds on

   Scatter the dust-fine seeds thinly and only press them on gently. Foxglove is a light germinator, so no soil goes on top. Sow too densely and you will have a harder job pricking out later. A knife tip of seed is enough for a whole tray.

3. Keep moist and bright

   Place the tray in half shade and keep it evenly moist. Water from below or with a fine rose, otherwise you wash the seeds away. At 18 to 20 degrees the first seed leaves show after 14 to 21 days.

4. Prick out

   As soon as the seedlings have two to three true leaves, separate them into individual pots or into the bed at 20 cm spacing. Handle them only by the leaves, never by the tender stem.

5. Plant out by September

   Set the strong young plants in their final spot by mid-September at the latest, so they still root before winter. Half shade with humus-rich, fairly moist soil is ideal.

The finest biennials for the border

Foxglove is the star, but it has good company. You sow these species by the same principle in high summer.

The second summer: from rosette to spike

After winter the rosette wakes, stretches, and within a few weeks the foxglove pushes its flower stalk into the air. The spotted bells open from bottom to top, and if you look closely, fat bumblebees crawl in head first. The pattern in the throat is no accident, it guides the pollinators like a runway.

That is exactly the trick against the gap the year after next: if you sow a small batch every summer, one generation always flowers while the next grows on as a rosette. That way you never have a flowerless year.

Letting them self-seed

The loveliest thing about foxglove comes almost by itself. Leave a few seed heads standing in late summer and the plant scatters thousands of seeds into its surroundings. The following spring you find small rosettes everywhere, which you either leave in place or transplant to the desired spot in early spring.

Such self-seeders wander through the garden and often find better spots than you would have chosen for them, gladly along half-shaded edges and between shrubs. A garden with foxglove, honesty and mullein always stays a little in motion because of it. If you want to steer the self-seeding, simply weed out the rosettes in unwanted places and let the rest have their way.

If you want to keep pure strains, say the white foxglove 'Alba', you should know: with free seeding the colours cross, and over the years the strong purple-pink usually wins out. Then you collect seed deliberately from the finest white plants and sow it separately.

Common questions about biennial plants

When is the best time to sow foxglove?

The best time is in high summer, from mid-June to mid-July, that is CW 24 to 28. The plant then forms a strong rosette by autumn and flowers the following summer. Sowing in late summer is possible but often leads to weaker plants.

Why does my foxglove not flower in the first year?

That is completely normal. Foxglove is biennial and forms only a leaf rosette in the first year. Only after the cold stimulus of winter does the flower spike come in the second year. If you want flowers straight away, buy plants ready to bloom in a pot.

Do foxglove seeds need to be covered with soil?

No. Foxglove is a light germinator. The dust-fine seeds are only scattered onto the moist soil and pressed on lightly, but not covered. Under a layer of soil they germinate poorly.

Does foxglove come back after flowering?

The individual plant dies after flowering, because it is biennial. But if you leave the seed heads standing, it self-seeds and you have new plants year after year. So the stand behaves as if it were permanent.

Which biennials can I still sow in summer?

Besides foxglove, mullein, honesty, sweet william, hollyhock and dame's rocket are suitable. You sow them all in high summer, they over-winter as a rosette and flower the following year. The principle and the timing are the same for all of them.