Harvesting dahlia seed from “Cafe Au Lait”.
How to Harvest Dahlia Seeds
Collecting dahlia seeds is a wonderful way to grow your own unique varieties. Unlike plants grown from tubers, dahlias grown from seed will be genetically different from their parents, so you never quite know what you're going to get!
Step 1: Leave the flowers to develop seed
Rather than deadheading, leave a few of your favourite dahlia flowers on the plant after they've finished blooming. The petals will fall away and the seed head will gradually mature. I harvest hundreds of seed each year but each seed head will produce up to twenty seeds.
Step 2: Wait for the seed heads to ripen
Ideally, leave the seed heads on the plant until they turn brown and begin to dry. This can take several weeks after flowering. Try to collect them before prolonged wet weather causes them to rot.
Step 3: Collect the seeds
Cut off the mature seed heads and carefully pull them apart. Dahlia seeds should be dark, flattened and pointed at one end. Separate the firm, well-developed seeds from the dried petals and other debris.
Step 4: Dry and store
Spread the seeds on paper somewhere dry and well ventilated for several days. Once thoroughly dry, store them in labelled paper envelopes in a cool, dry place until spring.
Step 5: Sow in spring
Sow your dahlia seeds indoors in March or April (or earlier if you have grow lights and heat mats). Your seedlings should flower in their first summer.
My top tip
Don't be too quick to discard an unattractive seedling. Some dahlias develop better flowers as the season progresses, and it's worth giving promising plants a chance before deciding which ones to keep.
The exciting thing about saving dahlia seed is that every seedling is a potential new variety. You might even discover something worth naming and growing for years to come!