In the Garden March 2016

By Peg Keenleyside

Along with getting myself one of those snazzy new Tesla electric cars, on my bucket list for this year is building or buying a self-watering raised bed for growing my must-have summer vegetables.

Self-watering containers have been on the market for years, and of course the raised bed has become the go-to model for growing your own vegetables, but recently the DIY gardening websites have started talking about a new kind of raised bed – one that has a reservoir for water built into the bottom of it.

In this new raised bed design, plants get watered not from the top, but rather from the bottom, drawing or wicking up water from the reservoir through their roots.

This new design is variously called a SIP (Sub-Irrigated Planter) or a wicking raised bed. This new method of growing vegetables is not to be confused with growing plants in a water solution only – called hydroponic growing. In these beds the roots of the vegetables are still nestled in soil as they would be in a traditional raised bed.

The difference is that below the soil layer is a reservoir that you fill with water. Plants take up that water on an as-needed basis through a permeable membrane between the soil and the reservoir. In this method, plants use up to 90 percent less water than they would through top-down watering.

Whether you’re a Point part-timer who just gets down on the weekend, or you’re a year-rounder in this rural paradise, the SIP bed or large self-watering container is going to take a whole bunch of worry and work out of the hot months of summer when vegetables need watering on a daily basis. The reservoir needs filling just every 2–4 weeks.

With another hot dry summer in the forecast I’m thinking this is the spring project to get started on.

For the Do-It-Yourselfer, building a self-watering raised bed starts with some online research at a website such as WikiHow, where step-by-step visuals show you how deep to construct your wood box in order to have the dual capacity for the earth and water reservoir you’ll need.

The DIY sites – including those ubiquitous YouTube videos – also show you how to build an overflow drain pipe into the box at the reservoir level and a standing pipe that comes up through the soil layer that’s used to get water into the reservoir.

Building these beds will, mercifully, not take a degree in rocket science and the equipment list is readily available at the hardware store and easy to manipulate with simple tools.

There are a couple of key elements to consider for the weekend DIY warrior, however. One is making sure that the liner at the bottom of the reservoir is sturdy and thick enough to prevent puncture leaks. Some sites recommend using pond liner material over builder’s plastic. If you’re interested in longevity for your bed, pond liner is the way to go.

There are also different types of medium that make up the reservoir structure. Choices range from a layer of lava rock or gravel spread over perforated PVC pipes, to pond reservoir blocks you can buy from pond supply shops or online.

One needs to also consider the permeable layer of material that will sit between the reservoir level and the earth level above it. Your best bet is going to be a top grade woven landscape cloth that won’t break down over time, preventing the soil layer from slumping through and clogging up your reservoir.

If this all seems too much like work to consider, then the answer to your self-watering bed dreams may lie online where large self-watering containers can be ordered with a click of your mouse!

The Terrazza brand SIP bed available online at gardeners.com, for instance, is a large freestanding white plastic affair, big and deep enough to grow vegetables in.

Most garden edibles will develop their root systems within the first 300 mm (about 12 inches) of soil and you want this area to drain well. The soil composition in your self-watering bed is therefore a big consideration in your plan whether you go DIY or pre-fab.

Like with a stand-alone planter, the soil needs to be about 40 percent (organic) potting soil, 20 percent compost and about 40 percent sandy compost. Some sleuthing around the Internet for “container garden” soil mix recipes will get you both soil composition recipes and pre-mixed order sources.

Top your whole bed off with a grow tunnel – hoops of flexible PVC pipe covered in lightweight plastic for rainy days or permeable sunshade fabric for the late summer – and you’ll be good to go.

Next up, my Tesla.