Wednesday, June 16, 2010

DIY deep-watering system

About the time I was first setting up my current garden, 9 years ago, I read about an ancient Chinese clay urn method of watering. They would bury an urn up to its neck in soil, fill it with water, and then plant seeds around it. The water moved through the wall of the urn to the surrounding soil by capillary action and spread out through the soil in the area around the urn.

This struck me as being a very efficient method of watering, with next to no water lost by evaporation, and with the water going directly to the root zones. In addition, the plant roots would head towards the water source and thus make the method even more efficient as time passed.

After a bit of trial and error, I came up with a design that uses ordinary terracotta pots with a top diameter of about 15cm. The cost of these might normally make this method prohibitively expensive, but fortunately I was able to buy around 200 of these at a fraction of their normal cost at a clearance sale.

The picture below shows how I put two pots together to make roughly an urn shape.

I used silicon (either bathroom or guttering silicon is fine) to stick the two pots together and to seal up the hole in the bottom of the bottom pot. The hole in the top upside-down pot is used to fill the pots with water.

Most of the perennial sections of my garden are watered this way. In each section I laid out ordinary 13mm poly irrigation hose, in a loop where possible, with the poly hose running past about 20 of the buried pots. An off-take tube runs from the poly hose to each pot and is poked into the hole in the top of the buried pot. You can see what I've done in the next picture because this raised bed is newly planted (raspberries under the rope trellis, and strawberry crowns around the edges). Once the plants grow the watering pots will be largely hidden by foliage.

This watering method has been (and still is!) very effective for my perennial plants, shrubs, and fruit trees, but with my clay soil, it is not very effective for germinating seeds or supporting young plants that still have under-developed root systems.  So, even though I like this system and use it in much of my garden, the only veges I use it for are perennial ones (such as asparagus). In the past, when I did use it in vege patches, I found I needed to supplement this watering system with surface watering during the first half of the growing season. I suspect you would need almost perfect soil to rely entirely on a terracotta pot watering system in a vege patch.

Using this watering system has had one unforeseen effect - the interiors of the pots make a perfect hiding spot for slugs. This could be seen as a disadvantage, or it could be seen as an effective way of trapping slugs! If you let the pots fill to overflowing with water, the slugs all crawl out of the top hole and accumulate on top of the pot. You can then dispatch the slugs in whatever way you see fit.

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