@sairhardyGb3DP3h7, did you sow them directly into the ground , or sow indoors and grow them on before planting out? It may be that they didn't have enough time to get established and form flowers.
@AnniD i put seeds in a pot indoors then outdoors when i thought strong enough (a bit of Google!) So yes maybe they didn't have enough time.... Im a beginner 😏!
You can do both, pot them up in Spring and when shoots are 3-4 inches high cut them off plus a tiny bit of the tuber if you can. Pot into compost and keep somewhere warm, ask if you're not sure how to "do" cuttings. Keep them just moist they rot easily if too wet. The mother tuber will happily grow new shoots and can be planted out. I've been told that folk who show plants say you get larger flowers from cuttings. You can also divide tubers in the Spring and grow on. I'm in NE England pot up at the end March putting the pots in a cold greenhouse and my coldframe, I don't do cuttings I'm a splitter. My dahlias are still flowering their socks off.
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It may be that they didn't have enough time to get established and form flowers.
Im a beginner 😏!