Can I use a heat pad under this? I'm starting seeds in a fully-enclosed, but unheated utility room. Typically I only see heat pads underneath trays that don't utilize a water bed underneath - so I don't want to heat just the water and encourage mold growth around the roots. Maybe I should just use a grow light instead? (asked on Amazon, too - sorry to duplicate!)
Yes you can absolutely use a heat pad under these trays even with a water bed. We do this exact same thing when we grow our seedlings with great success.
I purchased one of these kits over the winter and am getting ready to try growing annuals from seeds for the first time. While researching, I've seen some systems use a flat sponge-like sheet for holding water. Is this necessary? Also, what is the recommended level to fill the water? Thanks!
Rockwool cubes? You can certainly use those. They work very well, especially for beginners. Alternatively, you can use you a soil or potting mix to start your seeds. Best to put a 1/2" of water on the bottom and use the dome to retain the humidity. Without the dome, you can also fill the bottom tray with water just so it touches the bottom cells, wicking up the water. In order to avoid over saturation, a little air blowing in the room is using good propagation practice. If you want to avoid using the dome at any point and also want to avoid lots of water, just be sure to mist your seedlings a few times a day. Hope this helps!