Growing dahlias from seed
Dahlias must be one of the best value flowers you can grow. From mid to late summer they produce an abundance of blooms that keep on coming (encouraged with a little deadheading) until the plants turn brown with the first frosts. The flowers come in a range of sizes, forms and colours, from crisp white, through pastels, to deep, rich shades. They make fabulous cut flowers, the petals are edible (although, to be fair, not always that tasty) and some do a brilliant job of feeding bees and butterflies. It's no wonder growing dahlias can become an obsession!
Dahlia tubers are easily available and can be saved from one year to the next. But if you really want dahlias to bring diversity and value for money to your garden, seed is the way to go. A packet of dahlia seeds will cost a few pounds – often less than a single tuber. From that one packet you can grow enough plants to fill a small border. You won’t know exactly what each flower will look like, as you do when planting tubers, but that’s part of the fun of growing from seed.
When & how to sow dahlia seed
Sow seeds indoors in early spring to give the plants time to grow strongly and produce flowers in their first summer.
You will need…
A small pot or a module tray
Peat-free multipurpose or seed compost
A packet of dahlia seeds
A seed tray or saucer to stand the pot or module tray on
Watering can with a rose
Labels and a pencil
Propagator or a clear plastic bag
Sowing dahlia seeds
Fill the pot or module tray with a good quality peat-free compost and gently firm it level. Sow the seeds onto the surface and cover lightly with more compost. How many seeds you sow will depend on the size of pot or modules you’re using. Try to give each seed enough space to grow and spread 3-4cm. Stand the pots on a tray and water gently until the compost is damp but not soggy. Label with the variety name and date. Keep the tray somewhere warm – a heated propagator is ideal to help germination along, but you can also put the pot inside a clear plastic bag which will help maintain humidity.
When the seeds have germinated…
After a couple of weeks, you should see the first signs of growth. Keep the seedlings warm and ensure they have as much light as possible. Water to keep the compost evenly damp.
The first leaves to push their way up to the light are the seed leaves. After these the ‘true’ leaves develop and this is a sign that your seedlings are ready to be moved to individual pots. Fill some small pots with compost and poke a hole in the centre that’s large enough to easily accommodate a seedling’s roots. Hold one seedling by its seed leaf and very gently ease it from the seed pot or module (using a label or pencil to lift the roots from below can help). Place the roots into the new pot and gently firm compost around them. The seedling should be planted so the compost is at the same level as it was in the seed pot.
Preparing your plants to grow outside
Grow your plants on in a protected, light spot until all danger of frost has passed. You will need to accustom the plants to outdoor conditions before you plant them out in the garden. Starting in about mid-May on a warm, dry day put your plants outside in a sheltered position for a few hours during the day and bring them back indoors for the night. You can gradually move them outdoors for longer and to more exposed positions during the day, still bringing them back under cover when the temperatures drop in the evening. After a couple of weeks, your young dahlias are ready to be planted out where they are to flower.
Where to plant dahlias
A sunny position with good, rich soil is best. Water the plants immediately after planting and again during dry spells. An organic slow-release or liquid feed will help keep the plants healthy and producing plenty of flowers. When the plants have grown to about 30cm in height, I usually pinch or cut out the main stem. This will delay flowering for a short while, but it produces a bushier plant that will produce more flower stems. I also remove the flowers as they fade to prolong flowering… unless I want to save seeds from the plant, but that’s another story!
Be sure to mark all the plants that you especially like so you will remember to save those tubers for the following year.
In the autumn
The first frosts of autumn will turn your healthy plants with their dazzlingly beautiful flowers to a fairly uniform brown. At this point, cut back the top growth. If you live in an area with mild winters, you can spread a mulch around the tubers and leave them in the ground to flower the following summer. Alternatively, carefully dig the tubers up, clean and dry them off, and store in a cool but frost-free place to plant out again next year.
Want to have a go at growing dahlias from seed? Dahlia ‘Bishop’s Children’ is a lovely variety with dark foliage and flowers in a range of yellows, oranges, pinks and reds. The plants look fabulous in a border, large pot or in the kitchen garden where the flowers attract beneficial insects by the dozen!