When can dahlias and tender bulbs be planted outdoors?
Wait until all frost danger is past. To give dahlias and other tender bulbs a head start, pot them up for a few weeks in potting soil and leftover nursery pots, and grow them indoors.
For instance, I put my cannas (which I overwinter in the basement), into nursery pots and tucked them in the garage (which isn’t heated but stays cozy compared to outside at night in earliest spring). I drag them out into the sun in the daytime, then back in. If you just had a few pots, you could do it indoors in the house in a warm spot.