We need more information. What bulbs and where? What technique are you using?

You can buy 'bulb fibre' for forcing bulbs over the winter or you can just use ordinary potting mix. But I am wondering what bulbs you are starting now indoors?

i'm going to be starting Dahlia. I have a guide that suggests that this is a good time to get them growing. I'll be starting them in shallow (something) with moist soil(?). I'll be using a heat mat and florescent overheads.

soooo...do you think I should use plain soil?

Thanks!

That is important to know. Dahlias are actually tubers rather than bulbs. Their culture is not the same as spring bulbs for indoor display.

Are they going to be planted outside in due course? If so you can just start them in damp peat or any general purpose potting mix because they are not going to stay in that medium long. Don't use garden soil.

I don't start dahlias early indoors since I don't have anywhere warm to grow them on, but you may want to check your last frost date. Early May is probably the soonest planting out date and if they sprout and grow rapidly now you will have quite a plant to house indoors until spring.

the tubers are to be planted outside. as katob points out...it's too early to start them as they can't go out until late may. it's hard to find potting soil without fertilizer in it. is it ok to use the fertilizer potting mix?

This link might help. Any general purpose potting mix will do.

great link floral_uk

thanks!