The term ‘wicking’ refers to the water reservoir in the bottom of the boxes below the soil; water ‘wicks’ up from this reservoir through the soil to the plant roots. It is a way of targeting water at the very part of the plant that needs it most – the roots – and reducing the evaporation that occurs when we water from the top of the soil. It is a great system for hot and dry areas, so for much of Australia in summer!
These wicking boxes are excellent for soft-leaved herbs like basil or coriander, as well as lettuces, chervil or Asian greens. Try as many plants as you like and see for yourself what grows best.
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What to do
1. Clean the box.
2. Drill a hole in either end of the box, about 10 cm up the sides from the bottom, to act as an overflow.
3. Cut the PVC pipes with the saw, so they finish about 15 cm above the soil line.
4. Drill some holes into the bottom third of the pipe.
5. Ask someone to hold the pipe upright inside the box (toward one end), while another person fills the box to about 5–8 cm with the washed gravel or bark chips.
6. Lay a piece of shade cloth or hessian, cut to size, inside the box on top of the gravel. It should touch the sides, acting as a barrier between the gravel and the soil.
7. Fill the box with soil, finishing about 5–8 cm from the top.
8. Plant your seedlings and add some mulch.
9. Add water to the reservoir by slowly running water down the pipe, until it starts to dribble out of the overflow holes.
10. Also water the top of the box, to help bed the new plants into the soil.
11. Make sure you regularly check the reservoir by looking down the pipe – top it up if it looks low.
12. You can make a water level tester out of a length of broom handle or dowel. Mark the reference level on the tester before you fill your box, after you have drilled the overflow holes. Place the box on the ground, and stand the dowel inside the box. Mark a line on the dowel just under the level of the overflow hole. Any time you want to check the water level, place your dowel in the vertical pipe until it hits the bottom, and remove immediately. Look to see where the water level is on the pipe, in comparison to the ‘full’ line.