What is a wicking bed? A fully contained, self-watering planting bed that uses capillary action to maintain consistent soil moisture. Wicking beds typically have a reservoir of water stored sub-surface that is passively drawn on by plants as they need it.
Where is a wicking bed appropriate? In very dry climates wicking beds can save enormous amounts of water by limiting evaporation loss. Very appropriate for low-maintenance Zone 1 Gardens. Principles can also be applied to larger production based systems, but the cost can be prohibitive. Depending on conditions (arid to semi-arid) it may be absolutely necessary.
How we built our wicking bed step by step
Future site and home of wicking bed.
Insert vertical standpipe into corrugated pipe, cut hole using razor knife.
Cut hole for standpipe in weed barrier. Slip wee barrier over standpipe and lay down on top of corrugated drain pipe.
Cut 1” hole in side of container using hole saw. REMEMBER this sets the water level, and thus the reserve volume inside the container. Set slightly above the height of the corrugated pipe (not below!).Insert drainage port from the outside, screw on female end on the inside of the container. Cut two small squares of weed barrier or shade cloth, fold over several time, pin between male and female ends, screw tight. Zip tie for extra security.
Lay in sand to keep edges of weed barrier in position. Fill hole in middle of drain pipe to create wicking column of sand from the bottom of the container.
Place layer of coarse mulch on top of sand layer to prevent leaching of top soil layers into the sand layers.
Layer in compost, soil amenders, compost tea, worm compost etc. Finish with top-dressing of compost followed by coarse mulch. Wet soil initially as you go to ensure balanced moisture and to get the wicking column working.
Plant! Fill bottom with water using the standpipe. Once drainage port overflows you’re at capacity.
Planted around the second week of March, 2014. Filled to capacity at time of planting.
6 Weeks post planting – peppers, tomatoes, kiwi, jasmine, lemon grass and tons of volunteer squash and gourds.
Water Usage w/ Initial Plantings: 2 gallons required to fill up to capacity as of 4/23/14
Approximate Water Storage Volume:
- V = (3.14)(2in2)(204 in) = 2562 in3
- 1 ft3 = 1728 in3 , therefore 2562 in3 divided by 1728 in3 = 1.48 ft3 of H2O storage
- 1.48 ft3 x 7.48 gal/ft3 = 11.1 gallon capacity in the pipe alone
Surface area of the bed is 10.6 ft2 of growing space.
November 2014 Update: The wicking bed went all the way through an extremely dry summer out here and made it until now with only 2 (count ’em!) refills! I just did a 3rd refill on 11/1/2014. Over the summer we grew a ton of tomatoes, butternut squash, and peppers in the bed, along with more perennial items like maypop, jasmin, lemongrass (see flourishing in the front), salad burnet and malabar spinach.
Water Use Math: 2 refills = 22.2 gallons of water + a top watering each time to ensure moist soil column ~ 25 gallons for 10.6 ft2 growing space. So we went from the end of April to the beginning of November, roughly 6 months, on 25 gallons of water = 2.36 gallons/ square foot for 6 months of growing.
What did work: Heat loving/tolerant plants (because its on a west facing wall) – jasmine, malabar spinach, lemongrass, salad burnet, tomato, peppers, squash and watermelon all worked great
What didn’t work: The kiwis had to be taken out because the bed is on the west wall of the house and they couldn’t hack the heat.
What’s new: As of November 2014 I’m trying Canna edulis and comfrey in the bed as we steer it towards a more stable, perennial-based food/medicinal planter. Updates in spring!