I start most of my annual vegetables from seed. I retired my old 400 watt energy hogging plant light and replaced it with a much more energy efficient LED grow lamp, and since I had scrap lumber, decided to build a dedicated seed starting shelf with an integrated self-watering system.
The shelf design is pretty basic — 2′ deep, about 4′ wide, and around 5′ tall — fit to the available space I had in my workshop.
I decided to set up only the top shelf for now, since I wasn’t sure I needed all of the space on the bottom shelf yet.
The next step was to add a plastic sheet to somewhat protect the plywood shelf underneath. It’ll still get wet, but it won’t be as wet as it would be if the capillary mat was directly sitting on the plywood.
I cut the capillary mat so that there are several strips that can be fed through the shelf and into the water reservoirs below.
The water reservoirs are cheap plastic oil pans, available at your local auto parts store; each one holds about three gallons of water. This is enough water so that you only have to fill the reservoirs once a week.
The capillary matting, once wet, will wick water up from the reservoirs.
You might be wondering how the heck the seedlings get water if they are in pots. The answer is that they are not in pots — I use soil blocks for seed starting, and the blocks sit directly on the capillary mat. The soil block mixture wicks water up directly from the capillary mat. This way, the seedlings get the water that they need from the bottom without being watered from the top. (Top watering seedlings can cause fungal issues on the young plant).
The last step was to add reflective sheeting around the grow chamber. This material reflects and diffuses light so that the plants get ambient light from their entire environment, instead of only overhead; this mimics nature more effectively and also helps the plants photosynthesize more and grow stronger.
I can grow about 280 plants in a chamber this size until they are large enough to move outside into my small greenhouse in late spring. So far, the top shelf has been (barely) enough to grow all the plants I start indoors, and the light is strong enough so that the plants harden off rapidly when they’re moved outside.