When Frances Greene checks whether she needs to water — the dill, collards and other vegetables — at a local garden, she looks a bit like an auto mechanic.
“Just as you can check the oil in your car, you can check the water level in the reservoir,” says Greene, 70, who volunteers with the nonprofit Urban Patchwork. She inserts a long bamboo pole into a PVC pipe that sticks out of the dirt, then pulls it out. Moisture is visible for about 10 inches up the bamboo — showing that the plants in this raised bed, with a reservoir under the soil, still have water.
Seven gardens at In.gredients, a microgrocer that is part of Urban Patchwork’s farm network, use this water-conserving method, called “wicking beds.” The concept of wicking beds (sometimes called “sub-irrigated beds”) can be observed by dipping part of a paper towel into water and watching the water move up the paper towel. In this same way, water will wick up into the dry soil of a garden bed, moistening the roots.
These beds save on water, Greene says.
“You lose very little through evaporation,” she says. “I think they probably refilled the water every two to three weeks.”
Greene says the frames for the beds were made out of wooden pallets, with extra wood to fill in gaps. A sheet of vinyl was stapled over the lower interior and the ground. (Being economical, they used old banners from outdoor events such as races.)
“You have made a basin and given a waterproof lining to it,” she says. Then they set a plastic pallet on a ledge about halfway up the inside of the bed and drilled holes through the plastic.
After putting a knot in pieces of polyethylene rope, they threaded a length of rope through each hole in the plastic barrier, to “wick” up the water into the soil. (The knot keeps the wick from slipping into the water.) On top, they added a mixture of topsoil, sand and compost for most of the beds.
A PVC pipe runs the entire height of the bed, from reservoir, up through the soil to the open air. Water is refilled through the pipe, which needs a cap on top.
“This is a way to have a water reservoir without mosquitoes,” she says. “It’s not open to the outdoor air.”
They occasionally need to water on the surface if they have planted seeds or transplanted seedlings, until the roots have started, she says.
There are multiple ways to make wicking beds, from raised beds, to in-ground beds to container gardens. Numerous web sites have do-it-yourself instructions, and YouTube videos offer tutorials. At www.globalbuckets.org, gardeners can learn to make wicking planters out of two five-gallon buckets.
In the book “Incredible Vegetables from Self-Watering Containers,” author Edward C. Smith says a wicking system “takes water from the reservoir and moves it to the soil. In some containers, the wick is a piece of capillary matting, analogous to the wick in a kerosene lamp. In others, some of the soil comes into contact with the water and serves as a wick; the water then moves by capillary action up through the soil.”
In addition to water savings, Smith writes, the plants require less fertilizing because nutrients won’t get washed away.
John VanDeusen Edwards, co-founder of the nonprofit Food Is Free Project in Austin, is trying to spread the word about wicking beds, especially using salvaged materials, to grow edibles.
Since 2011, Edwards says, he has experimented with different ways to construct wicking beds.
“There’s no one right or wrong way to do it,” he says. With materials on hand and some planning, he says, “I’m pretty confident that anyone could build one in an hour.”
During an incredibly hot summer, plants watered with this method thrived, and Edwards realized that this was a feasible way to garden, with minimal upkeep.
“I didn’t have to water for all of August,” he says. “That just blew my mind.”
He and co-founder Jonathan Horstmann encouraged and helped 18 neighbors on a Central Austin street install wicking beds. The Food Is Free Project website (www.foodisfreeproject.org) posted a video that explains the steps they used to build the beds (which differ from the wicking beds at In.gredients).
First, they assembled four sides out of wooden pallets and set it in a level area of ground, “to make sure water is getting to all sides of the bed,” Edwards says.
They covered gaps in the pallet wood with corrugated plastic (using old campaign signs), and lined the bottom half of the bed with a waterproof tarp, to create the reservoir. They filled this with about 6 inches of tumbled crushed glass.
They installed a PVC pipe with holes in it at an angle, for drainage. A PVC pipe also is placed vertically up the height of the bed for refilling water.
Next, they added a sheet of burlap atop the crushed glass to separate the soil and the reservoir. They put soil on top of the burlap and started planting.
“The burlap is breaking the surface tension of the water,” Edwards says, in the video. “Just the same way a candle wicks wax up the flame … as the soil above it dries out, water will rise up through the fabric and go from where it is moist to where it is dry. So it will naturally water it, automatically.”