is it too early to plant Dahlia tubers

Definitely too early to go out . I have a few kept under the greenhouse staging that I've just begun giving a drop of water to every now and then.
Most of mine however are left in the borders .They are covered in mulch with a big upturned flower pot over them, during the recent warm weather I have been removing the pots during the day.

 

thanks

 

If you potted the corms into damp compost then personally I would not water until you see young roots appearing. Corms are like bulbs and pretty well have everything they need to start to regrow without intervention. I have the likes of Turk’s head Lillies and fancy Alliums potted up for the charity sales I run. They have had no water whatsoever ever since being potted up in October into damp compost and kept in a cold greenhouse. All are now showing considerable growth so they got watered last week. It is much better to under rather than over water anything in a pot which is not actively growing in my experience.

 

How deep do you plant the tubers? I'll be leaving mine in the growhouse for a couple of weeks

 

A couple of inches of soil over the top of the tubers is ok, IMO, you can plant deeper if you intend overwintering them in the ground. But then if you mulch them over before winter that's not a problem.

 

I don’t plant deep at all but because of my climate I always have to lift them Usually the corms are still visible above ground with say about 3/4 of the corms below ground.