How Can You Grow Dahlias From Seed?

How can you grow dahlias from seed?

Dahlia seed needs warmth, light and time. Sow indoors in spring, grow the seedlings on somewhere frost-free until the weather settles, then plant them out into their final position once the danger of frost has passed. Unlike tubers, seed-grown dahlias won't come true to a named variety, so if you sow a packet of mixed seed you'll get a genuine spread of colours, heights and flower forms rather than an identical set of plants.

This makes seed the cheapest way to fill a border or cutting bed, and it suits gardeners who like a bit of unpredictability more than it suits anyone chasing an exact show variety.

Dahlia growing procedure

• ›Sow indoors in March or April, six to eight weeks before your last expected frost, sowing any earlier just leaves seedlings sitting too long on a windowsill.
• ›Fill small pots or modular trays with peat-free seed compost, sow seed around 1cm deep, and cover lightly with compost or vermiculite.
• ›Keep at 18-20C, a warm windowsill or propagator works well, since dahlias germinate poorly in cold compost, and keep the compost moist but never waterlogged.
• ›Seedlings usually appear within 7 to 14 days, once they have their first true leaves, pot them on into individual pots to keep them growing steadily.
• ›Pinch out the growing tip once plants reach around 15cm to encourage a bushier, sturdier plant rather than one tall stem.
• ›From late May, harden plants off over 7 to 10 days, giving them increasing time outdoors, before planting into a sunny, sheltered spot once frost risk has fully passed.

Maintenance of Dahlias

Dahlias are hungry, thirsty plants once they're established, so consistent watering and feeding through summer makes a real difference to flowering. Water deeply during dry spells rather than little and often, and feed with a high-potash fertiliser every couple of weeks once buds start forming.

Deadhead regularly to keep new flowers coming, taller varieties benefit from staking early so the stems don't snap once they're heavy with bloom, and it's worth checking new growth for slugs and earwigs, which both have a taste for young dahlia foliage. In autumn, once frost blackens the foliage, tubers can be lifted and stored somewhere frost-free over winter, or left in the ground if your soil is free-draining and your winters mild enough. If you'd rather not manage watering, feeding and lifting yourself, our garden design and landscaping service includes seasonal planting care so beds stay looked after through the full growing year.

Are dahlias difficult to grow from seed?

Not particularly, they're one of the more forgiving flowers to raise from seed, germinating readily in warmth and growing fast once established. The main challenges are protecting young seedlings from frost and keeping up with their appetite for water and feed once they're in full growth. Soil matters too, dahlias dislike waterlogged ground, so heavier clay soils like those found around parts of Fulham need improving with organic matter before planting, while the lighter, free-draining soil around Chelsea suits them with far less preparation.

Can you just scatter dahlia seeds?

You can direct-sow outdoors from late May once frost risk has passed, but scattering seed straight into a bed loses several months of growing time compared with starting indoors in March or April. Direct-sown dahlias also germinate less reliably outdoors, exposed to slugs, birds and unpredictable weather, so while it's possible, it's not the most efficient route to a full season of flowers.

Do dahlias flower in the first year from seed?

Yes, dahlias are unusual among tuberous plants in that seed sown in spring will typically flower the same year, usually from midsummer onward if started indoors in March or April and planted out in late May. Each plant will also form its own tuber by autumn, which can be lifted and stored to grow on as a fixed variety the following year, giving you a plant with a known flower colour and form for future seasons.