Dahlias are quite easy to raise from seed and will flower and form a tuber within one season if sown in spring. The only way to get a dahlia to be exactly the same as its parent is to propagate vegetatively - that is by taking cuttings or dividing up tuber clumps. Seedling dahlias are NOT the same as the plant the seed came from.
Dahlia genetics are complex. You can even collect several seeds from one seed pod and the seedling plants can have very different colours and variable shapes! Basically, every dahlia grown from seed is a unique variety!! You just have to decide which plants are worth keeping. Dahlia breeders often say they only keep about 10% of the plants they raise from seed each season. You can try and do you own cross-pollination, or let the bees do the work. There will often be quite a few single flowered types amongst your seedlings, as 'single flowers' are a dominant genetic trait. Also, if you do have single types growing, the bees find it easier to get to their pollen - so they are likely to spread it around more amongst the other dahlias in your garden.
Examples of parent plants and seedlings that grew from their seeds:
Growing Your Own Dahlias From Seed
Seeds can be sown straight in a seed tray, but they need a little warmth to germinate - around 20 degrees celcius. Sometimes not all collected seeds come up. You will need to protect your seedlings from frost. If you want to save on seedling space, you can germinate them before placing them into seed raising mix and then discard the seeds that don't germinate. This is the method I followed:
1. Check viability - hold a seed between your finger and thumb. If it bends really easily, it is proabaly not viable. Good seeds are firm and quite dark in colour.
2. Lay seeds in folded damp pieces of cloth (or paper towel). Label and put in a container that keeps the moisture in (e.g. a Ziploc bag). Keep in a warm place at around 20°C. (e.g. on top of fridge or in hot water cylinder cupboard. Make sure it isn’t too hot). Germination may start from about day 5.
3. Check each day or two for germinated seeds (showing a white root). I found not all germinated. Some seeds may not have been properly mature when collected, others just rotted.
4. Once germinated, they need light. Each couple of days, I planted sprouted seeds in punnets of damp seed raising mix. Add labels at the time of planting. The punnets were put inside lidded, clear plastic 40L storage boxes in a sheltered spot outside (brought inside at night if there was a chance of frost). Filtered light is good, full sun with the lid of the box on will literally cook the seedlings.
5. This picture below is of about 3 weeks of growth. Once true leaves are showing (more serrated), prick them out so there is one seedling per cell of the punnets. These were started in the last week of September, but you could start earlier if you can keep seedlings protected until the chance of frost in your area is over. I planted them out when they were 15-20cm tall. They had good root systems and grew tubers and almost all flowered in one season.
