While looking for the cost of organic tatsoi on the web (research for my New Year's resolution), I ran across someone who wrote a thesis in the '90s about raising vegetables on roof tops. Though it didn't give me the answer I was looking for, I couldn't help but read it.
The article was a bit dry, not that that would deter me from reading it. His beds had soil that was only 3" deep to keep the roof from collapsing, but he did succeed in growing things. Sadly he concluded that it wasn't an economically viable enterprise. The useful tidbit that I got out of it was from his use of soil blocks.
Since I'm trying soil blocks this year and they can be eroded by watering from above, I've been contemplating how to water them. I had decided to just bottom water and hope they hold up. I don't like the idea of misting the little seedlings which is the recommended solution. It promotes disease in our humid area. However this author watered with a capillary mat. Yes! That is the perfect solution. I think even my husband can take care of my seedlings with a capillary mat.
I'm not using the author's route to a capillary mat which was buying a commercial one. Surely one would be easy to make with materials at hand. I have lots of cloth of different kinds: leftover bits from making things, old t-shirts and the like. I'm sure I'll find something that will prove appropriate after a little bit of testing. Before testing however another web search was at hand. What do other people use? I've found the most often recommended cloth is an old acrylic blanket.