What is a wicking bed?
A wicking bed is a self-watering pot. It is a growing plant method in which water wicks up from an underground water reservoir via capillary action.
It reduces water consumption by up to 50%, which is a big difference compared to the standard growing systems since evaporation is greatly reduced. If you want an efficient way to use water in the garden, I recommend giving a wicking bed a try!
The wicking bed’s objective is to prevent the water from exiting the base using a waterproof layer or lining. It creates a water reservoir below the soil. Instead of delivering water from above, the water wicks up into the soil from below, keeping it moist to ensure better growth and development of the plants you will cultivate.
How deep should a wicking bed be?
A wicking bed has several advantages compared to the conventional irrigation system, especially with its ability to ‘self-water’ without a control timer.
The difference with the systems that require programming to anticipate the plant’s needs is that a wicking bed provides water directly to the roots of the plants when needed. With this approach, there is minimal wasting of water via evaporation, which is further reduced via good mulching practices.
Before considering how deep should a wicking bed be? you need to learn the basics first.
For most experts, the upper limit in terms of soil depth for a wicking bed should be 25 cm. It is the highest distance water can be drawn up through the soil. Since most herbs and vegetables require the same soil depth for optimum root growth, it serves as ideal.
There should be a 25 cm of depth to hold the water reservoir below. Take note that a large body of water to draw from will make your wicking bed effective over a more extended period, such as a few weeks if you are going to leave your plants during the holidays.
When creating a wicking bed, make sure that the vessel is around 50 cm deep.
When this is your first time preparing a wicking bed, the initial step is to line the base, which will serve as the reservoir using a rigid, non-porous lining that holds the water in place.
Make sure that the lining is driven securely alongside the walls and into any angles. Doing this will ensure that there is a smaller amount of pressure on the material once it is occupied with water and scoria.
Note that any miniature punctures or rips allow the water to leak and can be challenging to fix. In case you are on a budget, you can utilize a dense builders film, but you should stay on the safe side by applying double layers. Otherwise, a pond liner will serve as a foolproof option but can be more expensive.
The next step is to work on the components that supply water in and out of the wicking bed. An inflow outlet that will fill up the reservoir must go to the base of the wicking bed and rest 1 or 2 inches of scoria.
If water is left to stay in the reservoir, it might draw in mosquitos. With this in mind, the inflow passage must be plugged when not in use. Make sure that you will fasten an overflow valve on the side of the container. As stated earlier, the reservoir’s depth should be no more than 25 cm from the top of the wicking bed.
Once you fill up your reservoir, water that overflows from this valve is an indication that the wicking bed is full.
A close look at the wicking bed design
A wicking bed has a simple design. When it comes to the size, it is a personal preference and can differ from a small basin that you can place on a table or stand or an entire garden bed-sized system.
It is important to note that the standard sizes of wicking beds are based on the measurements of commercial raised beds or construction supplies.
Some often use railway sleepers for a large wicking bed, and the dimensions and materials you will use will base on their size.
In most cases, three railway sleepers are utilized to create a single level. Another option to consider if you want to save on materials is to dig a trench in the ground to serve as the water reservoir level. With this approach, the pond liner should be positioned below ground level with the outlet at the same height. It will allow you to use the two heights of sleepers instead.
Coated steel or galvanized raised garden beds in various dimensions can be used as long they have enough depth. Ensure that they are around 70 cm high to ensure a good depth of soil and sufficient space above the soil level to hold the mulch in place.
In case you prefer a smaller container that is not deep, you do not need a 20 cm deep water reservoir. Simply scale it down to match the dimensions of the container.
Types of wicking beds
Today, you might find wicking beds that have reservoirs with media and media-less beds.
Reservoirs with media
The majority of wicking beds that you can create yourself typically focus on using media.
With this type of wicking bed, a media is used, which is a layer between the soil and the water reservoir as the wick.
It is a simple and affordable way of supporting the soil over the reservoir. The widely used medium is gravel, but other materials are available in the market that works equally great.
When creating a wicking bed, it is vital to ensure the correct depth. The depth of a water reservoir with media should be at or lower than 300 mm as the capillary movement struggles to drive the water higher than that level.
The soil above the reservoir functions as the wick. With this in mind, the soil layer must remain between 300-320 mm. The soil can be lower than this; however, the soil at the upper part will be dehydrated than the soil at the lower level.
I suggest making sure that the plants you will use can readily access the deeper soil levels with more moisture, such as tomatoes that can be planted deep into the bed.
Media-less wicking beds
Wicking beds that do not have media need a false base that allows the soil to be in a hanging position above the water reservoir. The wick arrangement can be made using a variety of materials.
What are the materials required for a wicking bed?
Creating a wicking bed requires several materials. Once you decide to create one, you need the following materials:
• Elevated garden bed. A prefabricated steel elevated garden bed or prepare a garden bed supported by timber.
• Pond liner. The pond liner you can use can be either made of PVC or the superior butyl rubber. Ensure that you have enough liner, which serves as a lining on the raised bed’s flanks and base.
• Coarse scoria. A permeable volcanic rock that you will use to fill the water reservoir. Take note that the water fills up the scoria level and wicks up. Remember that you need adequate amounts to fill the raised garden bed to a level of 20 cm.
• Geotextile fabric. The fabric serves as a barrier that divides the soil from the scoria-filled water reservoir. As a synthetic material, the geotextile fabric will not break down.
You can find it in the market as a superior grade weed mat, strikingly looking like a transparent cloth and available in gray-black or white. Since it is relatively thin, you should double the layer.
If geotextile fabric is not available, an alternative is a shade cloth with a high level of shading factor, ideally 90%, so that the holes are smaller in size.
Depending on the material you will use, make sure that you have sufficient to cover the raised bed base and extend slightly around the sides by at least 15 cm.
• Soil mix. Use good-grade soil with an adequate amount of organic matter. I recommend a combination of 50% premium soil, 25% organic compost, and 25% organic cow manure to provide your plants with a good start.
• Overflow outlet fitting. Utilize a 20mm threaded inlet and a drill with the suitable drill bit or hole cutter to create a hole to secure into the flank of the elevated bed.
• Inlet pipes. You should have two pieces of 50mm PVC pipe joined by a 90-degree elbow joint. Ensure that the pipe’s vertical segment extends above the soil level at a height that allows you to pour water comfortably but not too low that it is concealed among the plants.
The horizontal section must be around half to three quarters the length of the bed. It should be drilled around and over its length with holes around 10-12mm.
• When creating your wicking bed, you need a spirit level, a drill, drill bits, hole cutters, a group of small spring or screw clamps, and scissors.
How to Construct a wicking bed
• The exterior of the wicking bed is a manufactured raised bed. It is usually wood, steel, or any material durable enough to accommodate the required soil.
• The raised bed shell is padded with a pond liner to accommodate a large amount of water. The application of the lining transforms the bed into a substantial watertight vessel.
• A hole is created into the bed and pond liner so you can secure the overflow pipe at the level of 20 cm. It has the primary function of allowing water to move out once the water height is too high.
• The water reservoir padded with the pond liner is filled with coarse scoria or red volcanic rock up to the overflow pipe level. The layer will hold the water. The water will rest in the spaces amidst the scoria and wicks it upwards. It is important to note that the scoria level also functions as structural support to hold up the soil above it, away from the water below.
• The L-shaped inlet piping is secured in the proper position before the application of the scoria. It functions as a water inlet that fills the water reservoir with water. The vertical piping is affixed to the horizontal pipe using a 90-degree elbow joint. The horizontal pipe holds several holes that were drilled right throughout its length to allow the water to drain quickly.
• The scoria level is layered over with geotextile fabric to prevent the soil tier from dropping into the scoria level. It works as a barricade that divides the water at the base from the soil above.
• The soil then occupies the bed to a height right beneath the point of the pond liner. With this approach, the pond liner rests somewhat higher than the soil height.
The wicking bed is occupied with water via the inlet pipe. Once it is full, some water will move out of the overflow outlet. The water will wick up as high as possible to ensure that the soil stays moist.
When maintaining a wicking bed, I suggest flushing out the whole system at least once a year. If your wicking bed is undercover and not exposed to rain, it is best to flush it out naturally at least two times a year.
Remember that salt can build up at the upper layers of the soil. You should flush water from above to wash out the salt into the water reservoir and the outlet pipe.
As for fertilizer application, you should minimize when feeding the garden bed during the spring and autumn since it can accumulate in your wicking bed. Any amount of fertilizer that you apply will remain in the system unless you flush it out. Other than that, you can maintain your wicking bed in the same way as a raised bed.
If you want to make the most out of your gardening project, you might want to switch to a wicking bed in the next season. Remember that wicking beds offer several advantages over conventional raised beds. By being familiar with how deep a wicking bed is, you can prepare a wicking bed easily with the right materials.