
It has been hot, hot, hot in New York City and I've been worried about all the plants wilting. I've heard lots of people tell me that their plants looked great, until August, and then mysteriously, while on vacation, everything died. Well, it feels like August now, and I'm working on a design for a rooftop garden that has no water source. It's exposed to full sun and wind, yet has absolutely no irrigation. There's a drainpipe for run-off we wanted to attach to a rain barrel, but this too is set up so close to the door, and runs about 1 inch off the ground, so that nothing can be put around or under it, and it can't be altered.
So while researching self-watering containers, gel water crystals, and drought tolerant plants, (unfortunately, the client doesn't like yucca), I've come across some articles of interest. The Los Angeles Times published an article, How do his veggies grow? The no-dig way , about Pat Marfisi who has raised beds of layered alfalfa hay, straw, blood and bone meal, and compost, and it doesn't require much watering, and very little digging.
The Seattle Post Intelligencer weighed in last week with Green Gardening: I'll take my garden dry, on the rocks , and the key here is deep, gravel mulch. Foilage is planted in topsoil and compost, and then mulched with about a half-inch of crushed gravel. The author, Ann Lovejoy, wrote "Because these gardens are not watered (after the initial planting year), weeds rarely trouble them. The deep gravel mulches make pulling the few weeds that do appear a snap.... Why is gravel depth so important? Like any mulch, it is supposed to moderate soil temperatures and keep soil evenly moist. A 2- to 3-inch deep gravel mulch also will prevent weed seeds from germinating. A skimpy half-inch deep mulch won't.
Dry garden pathways often are trenched 12-18 inches deep, then filled with 3/4-inch crushed gravel. Like French drains, such paths pull excess water away from raised beds in winter, allowing plant roots to get plenty of air. This helps prevent the root rots that carry away so many plants during our long wet winters."
Last year, Slate.com published a good article, On Dry Land, which not only describes drought tolerant plants, but also tells how to prep the soil to retain rain water run off. The author, Constance Casey, advises, "Make the water percolate down to plants' roots. Don't till the soil; bare plowed soil loses water to evaporation. Leave organic material lying on the soil surface or plant groundcover (a cover crop like clover or alfalfa in the case of farmers). Midwestern farmers are now leaving corn plants up after harvest to catch the snow and protect the soil. Encourage worms, whose tunnels, about the diameter of a pencil, direct water down to root level."
If you're looking for drought tolerant plants, one of the best known suppliers is High Country Gardens