Large fast growing seeds (like beans and squash) plant well right in the gravel beds (don't know what type of planting method you are doing though.)
I've also used capillary matting to start seeds in peat pellets, I'm sure this would work well for many other seed starting medias too. I set capillary matting on some liner on a shelf and let the edge drape down into a trough of water and it kept the pellets nicely moist without the water logging that can happen if you leave the bottoms of the pellets standing in water.
Once the seedlings were well established, it is easy to pop the pellets into net pots, or into the gravel, or slide them into my zip grow towers.
When I get some more time I intend to improve on my seed starting shelves to add automatic top up or flow through on the water trough and test out some other seed starting medias on them like soil blocks, batting, rock wool, and whatever else I get my hands on easily.
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