On the QT | The Official Newsletter of GWA February - March 2017 - Page 18


Wicking Beds : Bottom-Up Sustainability

An ancient technology practiced by the Aztecs 2,000 years ago , wicking beds are gaining popularity for their sustainable use in gardening and urban farming . Basically , they use the design principles of selfwatering containers on a larger scale to garden sustainably outdoors . They are self-contained , raised beds that use capillary action to draw water from reservoirs beneath through a wick to the plant roots . This eliminates water wasted on off-target irrigation and reduces maintenance because the water reservoir can sustain plants for days or weeks at a time . The beds can be automated by adding a water-level sensor to refill the reservoir .
“ Wicking beds are gaining popularity in Australia for growing high-value annual vegetables for kitchen gardens ,” says Angelo Eliades , a passionate forest gardening advocate with Deep Green Permaculture , in Melbourne , Australia ( Australia is the world ’ s driest continent ). “ Typically only the most expensive veggies would be grown in a wicking bed , as the cost-per-square meter of gardening space is very high . This is a factor that restricts their widespread use . The capability of self-watering over an extended period is a blessing for school produce gardens , where the gardens are often unattended over the holiday periods , especially during the peak of summer .”
John Ditchburn , a lifelong vegetable grower with Urban Food Garden in Ballarat , Australia , notes that wicking beds use 40 to 50 percent less water than conventional garden beds . “ Wicking beds are usually made with timber sides and a pond liner at the bottom to act as a water reservoir , but they can also be made out of plastic tubs or any other container that holds water and does not corrode when in contact with soil ,” he says .
Wicking bed cross-section design shows the components of the system .
Since wicking beds are raised , they ’ ll warm up quicker in the spring than in-ground plantings , says Rob Avis of Verge Permaculture , Calgary , Alberta , Canada . On the flip side , that means they ’ ll freeze sooner in the fall and are more vulnerable to winter freezing and thawing . To offset this , he recommends attaching cold frames to the wicking beds , or covering them with insulating fabric for added protection .
Avis cautions that there is a physical limit to the distance that water will travel upward . “ When designing your wicking bed , it ’ s important to keep the depth of the media-filled water reservoir at or below 12 inches ( 30 cm ) as the capillary action struggles to lift the water higher than that . The soil layer should measure 12-13 inches ( 30-32 cm ).”
According to Ditchburn , the cost of building a wicking bed can be three to four times that of building a conventional raised bed of the same size . Eliades says , “ Building a wicking bed is a costly exercise , if done properly . There is a lot of embedded energy in the materials used , namely the pond liner , which also happens to be one of the most expensive components , and also one of the most critical ones . All materials have a finite life , so using a pond liner with a longer warranty will ensure that the wicking bed will have a long service life that will return the cost of the materials and offset the energy used to manufacture all the construction materials .”
If you ’ re relatively handy , wicking beds can be a do-it-yourself project . “ The skill level required