How and when do I sow foxgloves, wallflowers and other biennials?

Why biennials are sown in early summer rather than spring, the plant-out timing that gets them established before winter, and the self-seeding habit that means you only do this once.

Difficulty: beginner
Time: 40 min
Read: 4 min

Short answer

Sow in May, June or early July, the summer before you want them to flower. Grow them on in a nursery bed or pots, and plant them into their flowering positions in September or October so they root before winter. They flower the following spring or early summer, set seed and die.

A biennial spends its first year making a leafy rosette, overwinters, then flowers, seeds and dies in its second. That timetable explains everything about how they are grown: you sow them a full year ahead, which feels wrong and is the reason people who sow foxgloves in spring get leaves and wonder what went wrong.

What you'll need

Seed of the biennials you want
Seed trays or a nursery bed
Peat-free seed compost
Modules or small pots for pricking out (optional)
Watering can with a fine rose

Step by step

Sow in early summer, the year before you want flowers.May to early July is the window. Sown then, the plants have the whole of the summer and autumn to build a strong rosette, which is what carries them through the winter and produces a good flower spike.
Know which plants this applies to.Foxgloves, wallflowers, sweet William, honesty, forget-me-nots, Iceland poppies, Canterbury bells, verbascum and teasel are the common garden biennials. Angelica and some verbascums behave as short-lived perennials but are grown much the same way.
Sow into trays or a nursery bed rather than the final position.You want them somewhere you can water and weed easily through the summer. A spare corner of a vegetable bed works perfectly as a nursery.
Sow foxglove seed on the surface — it needs light.Scatter thinly and do not cover, or cover with the barest dusting of vermiculite. Foxglove seed is dust-fine. Water from below to avoid washing it away.
Prick out and grow on with space.Move the seedlings into modules or spaced rows in a nursery bed once they can be handled. A crowded biennial makes a small rosette and a poor spike.
Keep them watered through the summer.This is the phase people neglect because nothing appears to be happening. The size of the rosette by October determines the size of the flower spike next June.
Plant into flowering positions in September or October.Early enough that they root into warm soil before winter. Wallflowers in particular are traditionally planted in October, often after summer bedding comes out.
Space them properly at planting.They will be considerably larger by flowering time than they look in autumn. Follow the spacing on the packet rather than the size of the plant in your hand.
Leave them alone over winter.They are hardy. Slug protection is worth it for foxgloves in a wet winter, but no fleece or feeding is needed.
Let some set seed after flowering.Foxgloves, honesty, forget-me-nots and teasel all self-seed readily. Leave a few plants to seed and you never have to sow them again — you simply move the seedlings to where you want them.
Remove the plants after flowering.A true biennial dies after it seeds. Pull it out and plant something else, or let the self-sown seedlings take over the space.

Tips

Foxglove seed is extremely fine and one plant produces vast quantities. A single packet, or one seeded plant, supplies a garden indefinitely.
Wallflowers are traditionally bought as bare-root bundles in autumn, which is cheap and effective. Sowing your own gives a wider choice of varieties.
Biennial self-seeders scatter themselves in places you would not have chosen and are often better for it. Move the ones in the wrong place while they are small.
All parts of foxgloves are toxic if eaten and the sap irritates skin. Wear gloves when handling quantities of them and site them thoughtfully if small children use the garden.

Common mistakes

Sowing biennials in spring expecting flowers that summer — They flower in their second year. A spring sowing makes a rosette, sits through the winter and flowers a full year later than you hoped.
Leaving them in a crowded seed tray all summer — The rosette stays small and the flower spike the following year is thin. Prick out and give them room.
Planting them out in late winter — They root far better into warm autumn soil. Late planting gives smaller plants and poorer spikes.
Deadheading everything after flowering — You lose the self-seeding that makes biennials nearly free. Leave a few plants to seed.

Questions people ask

When do I sow foxgloves?

May to early July, for flowers the following summer. They make a leaf rosette in the first year and flower in the second.

Do biennials come back every year?

Individual plants do not — they flower, seed and die. But most self-seed generously, so a population persists in the garden without any further sowing.

Can I buy biennials as plants instead?

Yes. Wallflowers, sweet William and foxgloves are widely sold in autumn as small plants or bare-root bundles, which is the simplest route if you missed the sowing window.

Why did my wallflowers flower poorly?

Usually planted too late in autumn, or grown too crowded through the summer, so the plants went into winter too small.