Oversize EarthBox-style Bottom Watering Container

I've built a few of these over the past 3 years, and they have performed wonderfully, plants grew dramatically better than when planted in my garden. They are fairly easy to construct and almost completely maintenance-free. With low-transpiration plants like herbs, I only need to refill the water reservoir every 2 months.

Some Benefits of this type of bottom-watered container:

• Large surface area


• Large root volume


• Very low maintenance


• Steady moisture supply


• Steady fertilizer supply


• No electronics or moving parts.


• Very low water consumption


• Weed-proof

Principles of Operation

• Potting mix is on top, water is on the bottom


• Perforated divider provides aeration to the roots


• Water is steadily wicked up by capillary action via wicking columns


• Overflow hole prevents over-watering


• Plastic cover prevents soil evaporation, weeds and excess rainwater

1. Container
2. Any container of the right size that is strong enough to handle the weight and pressure. I'm using a 27 Gallon HDX container which is about as deep as capillary action allows (about 10 inches of potting mix). Lid is used as the divider.
3. PVC (4").
4. Used to support the divider. About 3 feet is needed (It's usually sold in 10 foot lengths). I use the perforated kind, fewer holes to drill (and more aeration).
5. PVC (1.25")
6. For the fill tube. Less than 2 feet needed
7. PVC Union (1.25")
8. To make a mosquito-resistant breather cap. If you cut it in half, you can make two.
9. Weedblock/Lanscaping Fabric
10. To keep potting mix from falling through gaps and holes. 4' width is a perfect fit, but you can overlap smaller pieces if you have to.
11. Screen material
12. To keep mosquitoes out of the holes. I'm using aluminum, but any outdoor screen will work.
13. Plastic Sheeting
14. To cover the top. I'm using "red plastic mulch", but anything will work.
15. Potting Mix (not soil!)
16. I used about 80 quarts of potting mix (two bags of Kellog's Organic).

Most of the work is in setting up the divider, which is made from the lid.

1. Drill the big holes. I am using two 4" wicking tubes, so 2 big holes.


2. Drill the small holes. This means lots of breather holes and one hole for the filler tube.


3. Drill tiny holes. This means lots of holes that you can use for zip-ties.


4. Now you can cut the lid - cut out the middle, then trim the outer ring. Do not cut through the ring - you will need it to hold down the plastic.


5. Cut the pipes. I cut the 4" pipe sections to 6" height. Also cut your filler pipe to length and slant the bottom cut so it doesn't sit flush against the floor.


6. Drill container holes. One or two overflow holes, once you know the exact height. They should be just under the divider height.


7. Cover the holes with some screen to keep mosquitoes out. I hot-glued aluminum screen over them.


8. Make a cap for the filler tube (optional). I cut a union in half and hot-glued aluminum screen to it.

• Zip-tie the support columns to the divider so it's easier to keep them lined up. Two of them should line up with the 4" holes in the divider. Ensure that they are distributed evenly to offer maximum support to the entire surface.


• Install the assembled divider and fill tube. Place fill tube on the same side as the overflow hole. Now remove the fill tube :)


• Line the big holes with fabric


• Line the whole thing with fabric. Hot glue may be helpful to keep it in place.


• Punch holes through fabric (wicking columns and fill tube).


• Reinstall the fill tube.


• You can now fill the container with potting mix.

1. Fill the wicking columns first, packing them down gently.


2. Water the potting mix as you go to help it settle.


3. Overfill the container to make a rain-shedding mound.


4. Create a trench down the midline and fill it with fertilizer. Balanced fertilizer is recommended (5 to 15 each N/P/K). The quantity is approximate (I am using a 2" line). Close the soil around it gently, do not mix it in. It will leech out over time.


5. Cover the surface with plastic. Be sure to poke a hole for the fill tube in the right place. Plastic should extend over the edges to allow rainwater to run off.


6. Install the ring.


7. Fill the water reservoir. If you used a 1.25" fill tube, you can just stick the end of a garden hose in for maximum flow.

Now you can plant

1. Cut the smallest slits you can work through. Vertical cuts may help reduce rainwater entry.


2. Plant your seedlings.


3. Water them from the top (just this once), you can lift up the plastic as needed.


4. If the seelings have very shallow roots, continue watering them regularly until they are established. The reason is that the very top of the soil may not have adequate moisture.

If you want to start from seed:

Starting from seed is tricky and requires perfect conditions. Because this container is so tall, the top of the soil will not receive enough moisture to sprout most seeds. You'll need to water them regularly until they sprout, and protect them from hot sun (some straw may help). It may also be possible to set up a temporary sprouting dome (though not a clear dome, so that the seeds do not bake in direct sunlight)

• If you don't use enough supports, your divider will collapse. This one was built with only 5 support pipes. You'll know that it's collapsing because the soil keeps sinking over time.


• Regular soil is not suitable for capillary action, so make sure that you use potting mix.


• You can make your own potting mix (google it) from sand, perlite and sustainably harvested sphagnum or coir. It will not be cheaper at big box store prices.


• How do I know when it needs water?
  
  
  
  
  • The container will feel light (you can lift a corner)
  
  
  • The plants are drooping (many will tolerate short dry spells, and may even benefit)
  
  
  • Automatic continuous water top-off isn't usually recommended for this reason
  
  
  • I've tried making a float indicator using a rod and some closed-cell foam, but it didn't work well. I don't find this necessary. You could use a clear hose and close the end with your thumb to check level, maybe.
  
  


• How many plants will it fit?
  
  
  
  • Herbs: Up to 12 (parsley, basil, cilantro). You can zig-zag/stagger them to give them more space.
  
  
  • Vegetables: 2-4 (tomatoes, cucumbers, peppers).
  
  
  • Roots: no idea.
  
  

This is what the parsley looked like when planted, and then two months later. I have not had to do anything with it at all. There is still plenty of water in the reservoir.

The basil is from last year, same story.

Update November 2021

I had some light frost (29F) that killed all the basil growing directly in the ground, but not in boxes (both in the same area). I suspect that the thermal mass of water and damp soil makes a difference.