So, vigilance is the key. I've been using 2kg yogurt buckets set up as a water well - stones at the bottom about 3 cm, small drainage hole at the side level with the top of the stones, a piece of shadecloth then the soil. Works most of the time, if I forget occasionally to water - which I do, enough water to drip out of the drainage hole.
Garlic chives at the moment, and had great success at getting roots to form on rhubarb transplants. Once again, the buckets can be recycled.