There is a small club of flowers that simply cannot be bought well in spring: foxgloves, wallflowers, sweet william, forget-me-nots. By the time they appear in garden centres, the best plants are the ones somebody sowed the previous July. That is the quiet magic of biennials — sow them in the next few weeks, in a spare tray on a shaded windowsill or a corner of the veg patch, and next April to July arrives pre-planted. This is the practical, step-by-step companion to our complete foxglove growing guide: exactly when and how to sow foxgloves and their fellow biennials, and how to get them from seed tray to final position before winter closes in.
- Sow June – early August, in trays or a seedbed
- First flowers April–July next year
- Sow alongside wallflowers, sweet william, forget-me-nots, hollyhocks
- Skill level easy — no heat or special kit needed
Why biennials are sown in midsummer
Biennials run on a two-year clock. In their first season they build only a rosette of leaves and a deep root system; in their second they flower, set seed and bow out. That means the sowing window sits, counter-intuitively, in the middle of summer: seed sown in June or July has three to four warm months to build a strong rosette before the first frosts, and the size of that rosette going into winter decides the size of the display next June. It is why foxgloves and their kin earn a permanent place in what to sow in July — and why gardeners who master this one habit always seem a year ahead of everyone else. If you have never raised any flower from seed before, skim our beginner's guide to growing flowers from seed first; biennials are among the most forgiving plants to start with.
The biennial timetable at a glance
June to early August — sow. Trays, modules or a nursery seedbed all work. Earlier is better: a July sowing makes a noticeably bigger plant than a late-August one.
August — prick out. Once seedlings show their first true leaves, move them into modules or 9 cm pots and grow them on in light shade.
September to early October — plant out. Set young plants in their final flowering positions while the soil is still warm, so roots establish before winter.
April to July next year — enjoy. Wallflowers and forget-me-nots open first, sweet william and foxgloves follow. Leave the last flower spikes to ripen seed and the colony re-sows itself for free.
How to sow biennials, step by step
The method below works for every biennial in the list; the only detail that changes is whether the seed is covered, and that depends on seed size.
- Fill and pre-water Fill trays or modules with fresh, peat-free seed compost, firm gently and water before sowing so the surface is evenly moist.
- Match the depth to the seed Dust-fine seed — foxgloves, forget-me-nots — is surface-sown and never covered, because it needs light. Larger seed — wallflowers, sweet william, hollyhocks — gets a light 5 mm sieving of compost.
- Keep bright, cool and moist 15–20 °C in bright shade is ideal; no propagator needed in July. Expect seedlings in 10–21 days — the fundamentals are in our germination guide.
- Prick out At the first true leaves, transfer seedlings to modules or 9 cm pots. Ventilate well — crowded summer trays are prime territory for damping off.
- Grow on outdoors Stand pots in light shade, water regularly and let plants bulk up through late summer into sturdy rosettes.
- Plant out in autumn After a week of hardening off, plant 30–45 cm apart in final positions by early October — not next spring.
Seed tray or open-ground seedbed?
Both routes lead to the same autumn planting-out; choose by seed size and quantity:
Trays & modules
Best for fine, light-hungry seed and small quantities.
- Full control over moisture and slugs
- Ideal for foxgloves, forget-me-nots and precious F1 seed
- Works on a windowsill, in a cold frame or outside
Nursery seedbed
The traditional route: a spare row in the veg patch.
- Raises dozens of plants with zero kit
- Perfect for wallflowers and sweet william by the row
- Thin seedlings, then transplant to final spots in autumn
Five biennials to sow this month
One sowing session covers the lot — a tray each is ample for most gardens:
- Foxgloves — freckled spires to 1.5 m that thrive in light shade; surface-sow and never cover. Browse foxglove seeds, including first-year flowering Dalmatian types.
- Wallflowers — velvet reds, oranges and golds with honeyed scent from April; the classic seedbed biennial. See our wallflower seeds.
- Sweet william — clustered cottage-garden heads and one of the best cut flowers you can grow; find sweet william seeds here.
- Forget-me-nots — the blue haze under spring bulbs; tiny, light-loving seed like foxgloves. Shop forget-me-not seeds.
- Hollyhocks — strictly a short-lived perennial, but grown exactly like a biennial: sow now for towering spires next summer. See hollyhock seeds.
Common mistakes when sowing biennials
- Burying fine seed — foxglove and forget-me-not seed germinates in light. Press it onto the surface; even a thin covering can halve germination.
- Sowing too late — a September sowing survives but makes a small rosette and a short, shy flower spike. Early August is the realistic cut-off.
- Letting trays dry out — surface-sown seed sits in the driest millimetre of compost. Mist or bottom-water daily in warm spells.
- Waiting until spring to plant out — spring-planted biennials never root as deeply and flower at half height. Autumn planting is the whole point.
- Tidying away the rosettes — first-year biennials look nothing like their flowers. Label rows and learn the leaves before the autumn clear-up.
Frequently asked questions
When is it too late to sow biennials?
Early August is the practical deadline for full-sized plants. Sow later and they will live, but go into winter small and flower modestly — worth doing only if you missed the window entirely.
Can I sow biennials straight into the border?
Yes — either in a nursery seedbed for transplanting, or in situ where they are to flower. Direct sowing suits larger seed like wallflowers; dust-fine foxglove seed is far easier to manage in a tray.
Will my biennials come back every year?
Each plant flowers once, in its second year, then dies. But leave the last flower spikes to ripen and shed seed and the patch renews itself — a rolling population that behaves like a permanent planting.
Do biennials need winter protection?
The classics here are fully hardy: their rosettes sit happily through frost and snow. The one thing they resent is winter-wet soil, so improve drainage at planting time rather than reaching for fleece.
Biennials are the cheapest theatre in gardening: one packet, one July afternoon, and a display next spring that would cost a fortune in plants. Browse all our seeds, dig deeper in our growing guides — and put one tray of foxgloves in before the window closes.
