One of the trickiest things new gardeners struggle with is watering. Wicking beds (better known as self-watering garden beds) take the guesswork out of watering.
The gist of how wicking containers work is easy. Water goes in the reservoir (the base), water holding material gets added, then a barrier to segregate the base from the soil above . The result is that your plants get watered through capillary action, and evaporation.
You’d be surprised by how much you can grow with hardly any intervening.
Here’s a quick guide on you too, can take advantage of self-watering garden beds…
The Materials You’ll Need
- A raised garden bed (or the material to build one).
The height should be 40 cm at least for a reservoir with a depth of 15cm and a 25cm soil bed. Ideally 60cm high, at most.
For the material to use, treated timber can be long-lasting, or you could opt for galvanized steel or another sturdy material that’s resistant to rust and rot.
- Liner
The interior needs to have the walls and base lined with a waterproof membrane. For this, you can use a pond liner, or similar material.
- Water Reservoir material
Use 7mm to 10mm crushed gravel for best results. Alternatives include river gravel, scoria, woodchips, garden mix, cocopeat, super soil, sand, sand and gravel mix.
- Plumbing supplies
Drainage material and a water inlet valve with a garden hose connector, plus a sealant to prevent leaking.
- Geotextile fabric
This is to keep the soil and water separated. Polypropylene sheeting or a similar geotextile fabric works.
Soil
Use a soil mix that’s appropriate to the plants you intend to grow.
Tools for the Project
- Spirit level
- A drill with a hole saw attachment
- A handsaw
- A Stanley blade or scissors
- A shovel
- A stapler
Step-By-Step Guide to Building a Self-Watering Garden Bed
- Level the surface
The frame needs to be built on a level surface to ensure even watering in the garden bed. If you’re building on a slope, make a frame support so that the entire base is horizontal. Otherwise, it’ll cause uneven watering.
- Build the frame
The height of the frame should be 40cm to 60cm. Any taller, the top soil is unlikely to get enough water from the wicking process.
- Line the interior with a pond liner or similar waterproof barrier
Lay the liner inside the frame folded. Working in sections, unfold it, push the liner into the bottom contours of the frame, pull it snug, and staple it near the top. Avoid stapling too close to the base as that could lead to leakages. Play it safe by stapling where the soil will be, not where the water will be.
- Attach the plumbing
For the plumbing, use a hole saw attachment on a drill to cut 2 holes in the frame to fit the size of the water inlet and drainage/overflow pipe. These go as close to the bottom as possible so that water can be emptied when required.
Affix those to the frame, sealing around the the fixtures to stop leakages.
The overflow pipe faces upward so you can use it to see how much water is in the reservoir. To drain the reservoir, the overflow pipe should be fitted in a way that allows it to be rotated to empty the water when necessary.
On the inside of the frame, cut the liner, feed the piping through the frame and apply a sealant around the fixtures.
Note: This is a good stage to add water to test that it is water-tight before proceeding to fill the reservoir with gravel or equivalent material.
- Add your reservoir material
As a rule of thumb, the depth of the reservoir should be filled to a quarter of the depth of the garden bed frame. For example, if you have a 40cm garden bed, fill the base with 10cm of reservoir material such as river gravel, scoria, woodchips, garden mix, cocopeat, super soil, sand, or a sand and gravel mix.
The reservoir material should be level. Use a spirit level to ensure that whatever material you use to fill the reservoir is level. There should be no puddling/pooling when water is added. If there is, tamp it down with your feet or a board, and add more filler material until there is no water pooling, indicating the base is level.
- Add the geotextile fabric
The geotextile fabric is used to keep the reservoir material seperated from the soil above. Polypropylene sheets or landscape fabric do the job.
- Add your soil
Fill the rest of the garden bed with the most appropriate type of soil for the plants you’ll be growing.
Maintenance Tips to Keep Your Self-Watering Garden Bed in Tip Top Condition!
- Watering a self-watering garden bed
Self-watering garden beds still need to be watered on occasion. Some of the reservoir will be topped up during the year from rainfall. The drainage or outlet pipe gives you a visual indication of how much water is in the reservoir. Generally, when the water level drops to around 10cm, attach a hose to the inlet valve to top up the reservoir.
- Draining a wicking bed
Flushing the soil is next to impossible in a self-watering garden bed. Excessive fertilizing can lead to a salt accumulation in the reservoir, or the soil could go anaerobic (giving off a foul smell), at which point, you’d want to empty the reservoir and start again. Do that by rotating the drainage pipe downward to let the reservoir empty.
It can be helpful to fill the reservoir and then empty it again to clean out salts from inside the reservoir.
- Winter drainage
In the winter when rainfall is heavier, it helps to angle the overflow pipe slightly to allow for more water to exit the reservoir. Consistent water will keep the reservoir full, in turn, keeping the fabric barrier in constant contact with the water, running the risk of root rot affecting your plants from consistently damp soil.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.