water, the clay pot turns into an amazing high-tech device. The micro-pores of the clay pot allows water to seep into the surrounding soil. A key characteristic is that the water seepage is regulated by the water needs of any nearby plant. When the plant's water demands have been fulfilled and the soil is moist, the water seepage from the clay pot will stop. When the soil becomes dry, water seepage will begin again. This seepage is controlled by soil moisture tension. It's automatic irrigation without timers or electronic sensors!Olla : Water Efficiency Combined with Liquid Fertilizer
Some designs (see below) allow you to bury the olla in the soil or potting mix. This allows the delivery of water directly to the plant's roots. No water is wasted. This is excellent for arid climates like in many parts of Africa. Finally, you may supply the olla with water mixed with liquid fertilizer. You'll only need about 1/4 to 1/3 of the fertilizer you would normally use. Although liquid fertilizer is more expensive than granular, it may end up costing less because of the tremendous efficiency of the delivery of the fertilizer directly to the plant's roots.
Combining Ollas with Global Buckets
Only one bucket is required and the use of power tools for drilling and cutting of buckets is eliminated. It's much more fun to caulk (required for clay pots) than to drill. We've begun (summer 2010) the testing of ollas in Global Buckets. So far we've had excellent results.
3 Steps to build your own Olla Global Bucket system:
Step 1: Build the clay pot. It's easy! Just glue two unglazed flower pots (or a pot and a saucer) together.
Step 2: Bury your clay pot into a bucket with just the top of the clay pot exposed. Use potting mix with dolomite.
Step 3: Keep the clay pot filled with water. After a month of hand watering (boring!), we're designing an automatic watering system (see below).
Step 1: Build an Olla
Seal the hole in what will become the bottom section of the clay pot. We bought a ceramic floor tile from Home Depot for 99 cents and broke it up into little pieces. Apply lots of waterproof silicon caulk around the opening and then stick a piece of the broken floor tile over the hole. We also caulked the other side (pot's exterior) of this hole with more silicon caulk just to ensure that leakage won't be a problem. 
Next you'll need to attach the two clay pots together.If you're using Gorilla Glue (as we do) you'll need to lightly wet one of the pots as shown in this picture.
We first use 100% waterproof Gorilla Glue. We let the Gorilla Glue dry overnight. We then put heavy amounts of silicon caulk over the connection (the Gorilla Glue leaves lots of tiny gaps). The end result is not very pretty, but it's watertight!
The finished product. We painted the top of the Ollas that will be exposed to sunlight with white paint. Since the top is now painted or glazed, evaporation will be greatly reduced. We learned this the hard way.If you click on these pictures to enlarge them, you'll see where the potting mix is moist from the olla.
Ollas (Clay Pots) in Developing Nations
This is an excellent Phd thesis from a student at the University of Pretoria on the use of clay pots in developing nations. Lots of great information.
This research paper is from the OAS (Organization of American States). It also relates to clay pot's use in developing nations.
Graham F Knight sent this link to a great pdf on Ollas in Africa.
Automated Olla Irrigation
The goal of this design is simplicity, leak-free smaller ollas and gravity feed (no siphons).
Materials:
a) 1/4" poly pipe
b) 1/4" "T"
c) 1/4" x 1 1/4" Fender Washer
d) Plumbing Epoxy Putty (it's waterproof, easy to handle and safe for humans)
e) Silicon Caulk
f) Terra Cotta Pot and Saucer
We used plumbing epoxy putty for everything, except when we used silicon caulk to attach and seal the saucer to the pot. We used two brands of plumbing epoxy putty. In the pictures, one brand is white and the other is gray. In the below right picture, that's gray epoxy putty we shaped into what looks like a cone to make a leak-free connection. The all important goal is to prevent leaks. Feel free to try different designs and materials. Let us know what else works.
That's white silicon caulk between the pot and saucer.
Some newly made "automated" ollas.
Burying a clay pot so it will be next to the plant's roots.
The Ollas are gravity fed from two 55-gallon barrels via a 1/2" poly pipe main line which branching off to the individual Ollas with 1/4" poly whips. We've refilled the barrels four times this summer (more often in the late summer, less in the spring). We add fertilizer (Dyna-Gro 9-3-6) to the water in the barrels so fertilizing is also automatic. Because we're using gravity, rather than atmospheric pressure, there's no need for the yellow small reservoir and float valves that you may have seen in the "classic" Global Bucket movies. The shiny metallic material next to the barrels is insulating material that we wrap around the barrels so they don't cook in our sunny Colorado summers.
We put four drainage holes in each olla bucket. We put metal screen over the holes so the potting mix doesn't fall out.
Note that our first attempt at automated Olla Irrigation resulted in leaks. This was because everything we tried to adhere to the slick 1/4" poly pipe wouldn't stick. In the above method, the putty is applied to the hard plastic 1/4" T and the metal washer.
Update August 7, 2010
All of the plants pictured below are irrigated with Ollas using our automated system described above. The plants are doing great. Also, we have not spent one second weeding this summer. The smaller tomatoes (front row) in the pictures were only planted about five to six weeks ago.
Update: Tomatoes May Not Work Well With Ollas
It's late summer now and the Olla experiment has been successful, but there are however, several observations to be made.
1) The single clay pot with the saucer bottom (see the automated irrigation section above) provided less water than the two clay pots glued to each other (see above "Step 1: Build an Olla"). This didn't matter until late summer when the tomatoes needed a lot of water. By mid-day on a hot late-summer sunny day, the tomatoes with the single clay pot with the saucer bottom had very droopy leaves. The tomatoes with the larger double clay pots seemed better. Next summer we're going to use real soil, as opposed to potting mix, in Grow Bags. The soil should retain water much better than the potting mix, and hence, maybe there won't be a problem using a single clay pot..
2) The soil in the spring and early summer was really moist from the clay pot irrigation.. It appeared that water-loving plants, like tomatoes, loved this. Some squash we were growing didn't seem to appreciate the wet soil as much.
Olla Q/A
Q: Should I bury the Olla, leaving the top exposed, or should I bury it completely underground? Anna Przychodzki of Brampton Ontario (Canada).
A: We did both ways and both ways worked. You'll find that the two clay pots glued to each other are really large and it may be difficult to completely bury it. And of course, if you're hand watering, as opposed to using the automated irrigation method, you'll need the the top of the pot exposed to pour the water into the clay pot's watering hole.
