This growing season, get rid of that watering can. While container gardening has long been an enticing option for eco-conscious apartment dwellers, the technology for doing so is evolving. The next frontier of urban agriculture is sub-irrigation. Advocates claim that this modern method can help combat everything from drought to poor nutrition.
So-called "self-watering" containers aren't really that. They are, however, self-contained systems that borrow concepts from hydroponics, oil lamps and candles, and micro-gardening. These sub-irrigation planters (a/k/a SIPs) work by wicking moisture up from a water reservoir into plant root systems. From the bottom up, a SIP contains a water chamber, a wicking medium of some type (usually perlite, a horticultural additive, plus potting mix), a drainage hole of some type (to prevent overflow), potting mix, and healthy plants. A fill tube leads from "above ground" into the reservoir, which needs to be re-filled every few days (no more twice-daily summer watering).
According to their devotees, SIPs are more productive (up to 50 percent more growth) and more efficient (using about 75 percent less water than traditional irrigation methods — i.e., top watering or even drip irrigation) because the water goes straight to the plants that need it, as opposed to evaporating into the air, running off, or being gobbled by weeds. Like raised-bed gardening, these planters eliminate concerns about toxins in urban soil. And SIPs are both portable and convenient: They can be placed anywhere where they'll get sun — including on concrete, decks, or rooftops.
"Simple-to-use personal food growing systems are safe, highly productive, produce no run-off and conserve water," read a blog post on Inside Urban Green (insideurbangreen.org), a website devoted to urban agriculture and container gardening. "Space in the sun for a micro garden system is all they need. Unlike dirt gardens, micro gardens or micro farms can be certified organic from day one. . . . Dirt gardening as the norm makes little sense in the city. If we really want to reduce obesity and hunger, we need to live in the modern world and use some very simple but highly productive technology."
There are several options if you want to go the SIP route this growing season:
• Purchase one ready-made. Some of the most popular options are the models available (online only, right now) at Home Depot and Lowe's (both cost about $30), or through the Gardener's Supply Company, which offers everything from hanging planters to window boxes to large raised beds for $20-170. The EarthBox Ready-to-Grow Kit ($55; earthbox.com) comes with the appropriate potting mix and soil nutrients.
• Make an EarthTainer. This is the SIP grandfather, developed four years ago by a man named Randy Newstead — a home gardener and Silicon Valley executive. A 20-page construction guide is available at earthtainer.tomatofest.com, including instructions for building the base unit out of two large plastic totes ("the new double-walled container-within-a-container design keeps the plant's root system cooler in the summer"), assembling the optional and removable cage system (for tomatoes or other plants that need vertical support), and filling the EarthTainer. Power tools (at least a drill and a jigsaw) are necessary. Newstead wants this information to spread beyond bourgeois backyards. "With the global food crisis escalating," he says on his website, "I believe that spreading knowledge worldwide of how to build EarthTainer growing systems could help feed hungry people in impoverished areas around the world. Not just heirloom tomatoes, but corn, soybeans, and other high-nutrient crops can be grown."