fill a container, the size of the one you are growing in currently, with soil. pick it up to see how heavy it is. then water it until some water comes out the bottom of the pot. pick it up again after the water is done draining out. When its wet it will feel that heavy. When its dry it will feel as light as the soil w/o water. over time you will get the feel for it. this method works well until your containers get larger than 5 gallons.

keep them a little extra damp while they are first starting out... like every 2-3 days depending on container size.