Note from Kirsten: Today’s DIY post is brought to you by Ken Charm. Ken works on the sales counter at our Everett location and recently got involved with Dunn DIY through the Northwest Flower & Garden Festival.
Ken studied environmental science at Western Washington University and worked as an environmental consultant for 14 years, so he knows a thing or two about working with various wood species in a garden setting. In part 1 of this series, Ken shared how to build the frame of a self-watering planter bed (also referred to as a planter bed, planter box, garden bed, etc.). Today, he’s sharing how to plant a garden—and make it self-watering. It’s all you, Ken!
Step 1: Add an Overflow
The beauty of this raised bed is that it's self-watering. To ensure your garden doesn't drown in moisture, add an overflow. Measure about halfway up from the bottom of the bed in a visible but out-of-the-way location and drill a 1 1/8" hole. The hole should go through the cladding, the frame, and the pond liner. (You'll want to use a utility knife to cut through the liner.)
Cut a piece of PVC from the 3’ pipe that’s just long enough that when you put the coupling on one side and an elbow on the other, there’s just a bit of that tube visible.
Glue the tube to the elbow with PVC cement and place the tube through the hole, leaving the elbow on the outside (facing down). Glue the coupling to the tube, trapping the liner and roofing in between. We’re trying to create a seal here.
Place some of the tubing (8” or 10”) into the coupling and place the elbow on the end of that. These last two pieces you don’t need to glue.
Take a small piece of the landscaping fabric you'll be using later, and place it over the end of the 3/4" PVC pipe. Use tape or zip ties to hold it in place. I also put a small, loosely balled-up piece of landscaping fabric in the PVC pipe end extending outside of the bed; this will keep critters from entering and clogging your pipe.
What we’ve created here is the overflow that tells when the reservoir is full. The elbow on the inside gives us some adjustability on how high the reservoir will be when it comes to the step where we fill it up with rocks.
Step 2: Add Perforated Pipe
Now that we have a PVC-elbow overflow to help with the self-watering drainage system, it’s time to install the perforated pipe (which holds the water the roots will wick up when they're thirsty). To start, place the pipe in the bottom of the bed. Put a cap on one end (this is important—it keeps soil from getting in) and an elbow on the other.
To make things easier, place the elbow in a convenient corner, then place a short, scrap piece of pipe into the elbow going straight up and clearing the top of the trim. Finally, add a cap to the top of that pipe. This is where the hose will feed through—so you'll have to remove the cap when it's time to fill things up.
Step 3: Add Rock
Once the pipe is laid, fill the bottom of the planter bed with 1 cubic yard of any small rock, as long as it’s smooth (pea gravel or gravel less than 5/8" is fine). Don’t use crushed rock—the sharp edges could damage the pond liner. Remember, a cubic yard is 27 cubic feet. Most bags of soil and rock you see at the store are about 1 cubic foot—do yourself a favor and have it delivered (or rent or borrow a pickup truck).
This is where things get physical. A cubic yard of rock—what we’re using here—weighs about 3,000 pounds. Go slow, and move that 3,000 pounds into the bottom of your planter box!
Step 4: Add Landscaping Fabric
After you’ve recovered from your rock-lifting workout, place landscaping fabric, jute, coir, or whatever barrier you’ve chosen (burlap coffee sacks work well, too) on top of the rock. The goal is to keep dirt out of the rock and any sneaky weeds out of the garden.
Step 5: Add Soil
Once you’ve laid the fabric, cover it with about 1 cubic yard of garden soil. The garden soil only weighs about half of what the rock does, so this won’t be as hard as all the rock you just moved. Once finished, take your hose and fill the pipes until excess water drains from the overflow tube. This step takes longer than you might think. (There were several times we thought the overflow was broken.) Don't worry—you'll get there with a little patience.
Step 6: Plant Garden
Plant the bed, and enjoy the wonderful results! When I recapped the project for this blog, I’d had one bed planted for about a month. The top of the soil looked dry, but a moisture meter—and the plants—told me that not too far below the surface, everything was doing well. I hadn’t watered the plants in weeks (though it is important to water them from the top as they get established), and nothing had died!
It might be worth adding a layer of mulch to the top of your bed—maybe an inch deep or so—to help keep the top layer of soil from drying out. Mulch will also continue to release nutrients into the soil as it further decomposes, keeping your soil in good condition—and your plants happy!—for years to come.