Ah, well dahlias should be started off in pots indoors or in a greenhouse - you pot them up and don't water, then as soon as growth starts, you start watering. Plant or pot outside mid to end of May, they're frost sensitive. Get yours out of the ground asap - with the wet weather we're having, there's a high risk they'll rot in the ground.

Thanks Bamboo :)

I leave mine in the ground all year - they even came through the winter before last. Mine are just peeping through. Mind you, we live in a relatively milder area and have extremely well drained soil.

I think the soil in Hampshire is over a clay substrate, like London, and mine don't survive outside here over winter.