Wicking beds

While on the hunt for a cheap pot or planter for my snake beans, I found this raised planter at Bunnings. Reading through the favourable reviews, I noted that many people were perplexed at its design; there were no drainage holes but for the end of the hollow legs, and there was a lip at the top of the legs that prevented all water draining. 

 

Fortunately, there were a few savvy gardeners out there that mentioned "reservoir" and, upon some light research, I came across the wicking bed (strangely, the product never markets itself as a wicking bed). I had heard of wicking beds from the Rogue Ginger and saw them in use throughout Northey Street City Farm. A quick search will point you to many resources on the important features of wicking beds and the many ways of building your own. Below is a small system based on the Fountain raised garden bed which I describe assuming you have done some research!

Here's what I used for the project:

• Fountain raised garden bed - built-in reservoir and overflow drain
  
• 1m plastic hose for water intake - can use any kind of sturdy hose that won't compress too much under weight of damp soil
• Secure cap to fit over one end of plastic hose - to keep mosquitoes and bugs out, and to prevent evaporation
  
• gravel, approx 10-15mm - enough to fill the hollow drainage legs of garden bed
• gravel, approx 5mm - enough to fill the reservoir
• small amount of charcoal bits - to keep water "sweet"
  
• water-permeable fabric with weave tight enough to hold soil - enough to line the garden bed
• equal parts quality potting mix and compost like mushroom compost
• light mulch like sugar cane mulch

Steps:

1. Place the wicking bed in its final position as once full, it will be very heavy. Consider how much sunlight, shade and protection from wind your plants will need.
2. Fill hollow legs with large gravel.
3. Make holes or cut slits through half the length of the hose, the opposite end to the cap. These don't have to be large or many; they are only there to allow water to drain into the reservoir more easily.
4. Lay out the hose with the drainage holes/slits sitting at the bottom of the reservoir and the capped end sticking out a little over the top of the garden bed. You will need to access this to top up the reservoir.
   

   

   Gravel in drainage legs and slotted hose in position.
   

   
   
5.  Put the charcoal bits at the bottom of the reservoir and then add the small sized gravel to the level of the overflow lips or large gravel. The small gravel will wick water up to the soil even if the water level is low.
6. Lay the cloth over the small gravel and line the sides of the bed. You can use expensive geotextile, but thick shade cloth or doubled-over lighter shade cloth will work, as will doubled-over burlap sack. Its purpose is to allow water to wick up from the gravel to the soil but stop the soil from falling into an clogging up the gravel.
7. Mix the potting mix and compost and fill the garden bed. You can fill it right up as it will settle down after a couple of weeks.
8. Fill the reservoir via the hose, but also give it a water from above to get it settled; you will know the reservoir is full when water starts draining from the bottom of the legs.
   
9. Add a layer of mulch to keep the moisture in.
10. Allow everything to sit for a couple of weeks before planting.

Tips and notes about wicking beds that are different to in-ground and pots.

• Watering from the bottom (reservoir) means that nutrients don't wash out like in pots. This also means that added chemicals like fertiliser won't wash out either. Use these sparingly.
• Sown seeds will need watering on top until roots establish enough to reach deep enough into the bed.
• Refill reservoir every week or two; you will get to know how quickly the water needs topping up. Larger plants and hotter days will use up water more quickly.  
• Only go as deep as 25-30cm of soil as this is the limit of its wicking ability.