Are you giving them a deep watering every few days? They need a lot of water once they have started growing. Swan Island suggests watering with a sprinkler for an hour or two every couple of days (depending on how hot it is where you are and how much rain you get). My first year of growing them was a failure and I think it was because I just let them get watered by the sprinkling system and they did not get enough water. They were all small and very few blooms.

Linda

Hm, that's a good idea, but I live in Portland, Oregon and we've had the wettest spring and summer on record in a hundred years. Could it be a lack of nutrients?

I've shared in the wealth of northwest wetness! Hasn't this been about the buggiest year that you've seen? I don't recall ever being kept so busy trying to spread organic pesticides. Once I get the pest stuff where it belongs so it can do it's job . . . multiple days of rain. So the next spell when it doesn't rain, I'm back out baiting, spraying, spreading . . . . Not my favorite year for dahlias. Particularly during the last month of July and I haven't seen my first bloom open. But finally, there's a little color in a few buds.

I've noticed that a dose of fish fertilizer every couple weeks does enhance growth in my garden. But I don't want blooms until my plants are large enough to support them. With the boost given by the fish fertilizer, finally I have a large number of plants that both have buds, and are healthy enough to support a bloom. The downside of the fish fertilizer is the lovely smell I am never quite careful enough so as to not bring it back into the house with me.

If you have enough water and sunshine, it might be the soil that is the problem. It would take sometime for your soil to take those fertilizers in before it could nourished plants like your dahlias.