Self-watering Mini-greenhouse With Europallets

Do you think that it is annoying to water your plants in your mini-greenhouses even though you live in a rainy climate? And to lift the lid every time you want to water? I have two mini greenhouses which fit exactly on Euro pallets and their pallet frames. The available self-watering systems were not fitting the same ground plan, so I decided to build my own. I was lucky to get most materials for free in my neighbourhood, so the available material influenced the design. I only bought the greenhouses and the pond liner.

The idea:

The water-collecting basin is slightly bigger than the greenhouse, so that it collects the runoff water. The soil is raised above the water level, only the pallet-“feet” reach into the water. They have holes and are filled with expanded clay, so that the water gets drawn into the upper soil. There are many systems beforehand, this type is simply ideal for pallet frame raised beds and greenhouses in that size. The pallets are very robust so they will bear the greenhouse, you just need the right type of plastic pallet. They seem to be very common in my area.

Supplies

Materials:

• 1 plastic Euro pallet (scrap material. One might consider the food approved version)
• 1 or 2 pallet frames (scrap, alternative build those frames yourself)
• 1 mini greenhouse (there are instructions how to build one online), I gave approximately 50€ but they are normally double that prize
• Wood (scrap, cross section 4cmx7.5cm)
• Ground plate (not bearing, only protection for the liner), scrap plywood
• Pond liner( I chose EPDM as material to avoid PVC, approximately 30 €)
• Screws/nails
• Optional 32l expanded clay
• Compost, garden earth
• Optional wood paint or oil

Tools:

• Electric Drill
• Chop saw
• Hand saw or jig saw
• Hammer
• Knife
• Drill bits

Step 1: Calculate Size of the Frame

Measure the pallet and estimate the offset needed to collect rain water.

I simply decided to use 1 time material thickness (4cm) for spacing, but more is better. You could start to sprinkle water on the roof to see at how much distance it hits the ground.

You want a height that the pallet and the outer wall are in line. The height of my material is exactly half the height of the pallet (15 cm)

• For the long sides I used 4 pieces á 120 + 2 x 4 = 128 cm .
• For the sides I used 4 pieces á 80 + 4 x 4 = 96 cm
• Additional 8 pieces á 14 cm as connector and spacer.

Liner:

• length: 120 + 2 x 4 + 2 x 15 + 2 x 4 = 166 cm + a little extra,
• width: 80 + 2 x 4 + 2 x 15 + 2 x 4 = 126 cm + a little extra

It is also a good idea to double check the length after sawing the first pieces by placing them around the pallet.before you saw the pieces.

Step 2: Build the Frame

• I screwed the long pieces to the connectors from the inside
• I screwed the shorter sides to the long sides from the outside
• I added spacer to the short sides as well.
• If you have thinner material, consider reinforcing the long sides
• Turn around and nail the ground plate on. It is not bearing if you put it directly on the ground, so I used some old plywood.
• Optional: reduce the height in a section to steer the runoff

Step 3: Put in Place and Level Out

I put the frame on my terrace and used the existing slope to have the runoff away from the house, but check if the slope is too big for the basin to fill. If you need to raise on end of the ground, remember to reinforce the ground plate or fill the area below completely.

Step 4: Add the Liner and the Pallet

• Put the liner approximately in place, it should be possible to raise it
  above the height of the frame
• My pallet had only holes in the bottom of the feet, so I drilled some extra into the sides at ground level to provide better water flow
• Put in the pallet
• Add some water to press the liner into corners and edges
• Nail the liner to the top of the frame
• Cut the protruding material off. You might want to save it as liner for the frame containing the soil.

Step 5: Add the Earth and Greenhouse

• Put one or two pallet frames on top of the pallet. I used it upside down so that I secures the greenhouse. With the spacer, it sits secure on the pallet, but one might secure it better in place
• I filled the “feet” with expanded clay and also a single layer on the pallet, but that is optional
• Fill the frame with compost (I used a mixture of 1 year old woodchips and 1 winter aged cow dung and a little healthy garden earth which converts into sphagnum-like structure with time)
• Put the greenhouse on top

Step 6: Finally:

Plant plants, which are craving much water, on top of the feet and in between plants that are more tolerant to draught. Water a few times thoroughly (better 1 time much and let the earth dry from the top then many times just a little water) in the beginning until the plants have established deep roots.

Step 7: Update After 4 Weeks

It really works!

When I wrote the instructable, I had tested the wicking-principle for tomato plants or cucumbers in the “feet” positions with the first greenhouse. It also works in between and also with plants with smaller roots. Just 4 weeks after I built the second greenhouse, the water reservoirs in both are nearly filled up.

I did not measure, how much water I filled in initially, but with the current situation it is clear, that both systems are collecting enough rain in this conditions to get through the summer. The first has only 4 cm opening to all sides for water collection (as described above). For the second, I increased the opening to 8 cm. In the second, the water level rises faster, but the first seems sufficient. During summer our average precipitation is higher than 50 mm, so even with higher evapotranspiration, there should always be enough water.

Now the tomatoes are outgrowing the roofs and the plants do not need frost protection any more. So during summer I will remove the roof so that it will rain directly on the soil. Thus all water will be collected in the smaller system where otherwise with heavy rain, a lot of the water deflects of roof and walls and ends outside the reservoir.