40. Capillary Bed Prototype
Design your own self watering tray.
I really like the self watering trays that I purchased from Gardener’s Supply, but at $20 each, they are a bit costly. With my new greenhouse set-up, I was looking for 30 more trays, so I wanted to come up with a cheaper solution.
Then I saw this video on YouTube: Making a Capillary Bed to Water Your Seedlings by Under the Choko Tree. I was inspired and decided to try to make my own.
Product List
Gardzen (Amazon) seed trays with lids, 10-pack ($31)
Gardzen (Amazon) trays, 10-pack ($17)
Playground Sand (free - we have a pile in the yard)
PVC Pipe (free - we had deconstructed an irrigation system) Version 2.0 doesn’t need this part
16 ounce Water Bottles (free - reused) Version 2.0 uses a different bottle
16 ounce (U-line) Banjo Sauce bottles ($57 for 36)
Cost Per Tray
The total cost of each tray was $6.38, which is about a third of the pre-made system. Had I purchased the 30 trays at $20 each, the total would have been $600. With my DIY trays, the total was $191.50.
Capillary Bed Design
My YouTube search for sand based self-watering trays started with research I was doing for my future hoop house. I was hoping to find a way to make watering easier since I do not have easy access to water in my orchard. Then I found this article from a class at the University of Washington about capillary beds: a capillary bed supplies constant moisture from the bottom of the plant, at the root zone.
Capillary and Wet Beds: Essential Tools for Restoration Propagation
Based on this article, I sketched out a diagram for my hoop house capillary beds:
Capillary Tray Design
Then a lightbulb went off, could I do the same for my smaller trays in the greenhouse? Here is my sketch for the smaller, self-watering trays:
Testing the Sketch
I was excited to test out my design, only to discover a fatal flaw: bubbles.
The bubbles meant that water gushed out. In this design, the rim of the water bottle was above the level of the sand. Either I would need to tape the bottle to the PVC pipe — which sounds fussy — or come up with a different solution to eliminate the air gap.
Google search: long neck bottles. Most long neck bottles are for larger volumes, which won’t work for me since I have limited shelf space. Then I came across the U-Line 16 ounce “banjo” sauce bottle — AKA ketchup bottle. The height of this bottle is just shy of 8” which works with my shelf height.
Capillary Tray Design V2.0
Upgraded design features a different bottle and eliminates the PVC pipe:
This design worked better, and no bubbles, but it also had two significant flaws.
Flaws:
When I turned over the bottle, most of the water gushed out.
The size of the bottle didn’t quite fit in the multi-cell tray, crunching the tray when I inserted the bottle
Solutions:
I added a cap to the bottle and drilled a 1/4” diameter hole into the center, this should reduce the speed of water flow
I decided to sacrifice the ability to reuse the tray in the future and cut out an area for the water bottle.
Capillary Tray Design V3.0
Upgraded design with cap and modified multi-cell tray:
Propotype
Photos of the prototype V2.0 on the left and V3.0 on the right; note how much water was lost in V2.0 compared to V3.0.
My next step is to create DIY instructions so you can make your own.