I have grown Redskin dahlias from seed for the past two years and they sprout and grow quickly for me. I plant out at the end of May and I won’t start my seeds until April. Redskin are about an 18” tall dahlia and their full-size tubers are more like golfball size. What variety and size are your ball dahlias?

I have grown dahlias from seed: they are generally trouble-free, germinating within 10 days from a late March/early April sowing. I don't use bottom heat, just sow a couple of seeds in 7cm square pots. Once the seedlings get their true leaves, I discard the weakest seedling-just cut off the top growth, don't try to pull the seedling out as that can damage the remaining seedling. I never need to pot up - 7cm2 is good enough for a single seedling until transplanting time (which will usually be the end of May in my climate).