Gone Potty II : irrigating with terracotta pots

The terracotta  pots I've buried in the garden beds have proven very effective thus far so I'm getting more. 

• See my earlier post: Gone Potty irrigating with terracotta pots and hand watering 

• and note the method --Buried Clay Pot Irrigation Action Sheet (good summary of the DIY)

A lot of wetpot/olla literature suggests you extend the height of the pot in order to bury it deeper. Indeed many are thrown on a pottery wheel as an urn or carafe shape. But looking at the dampness these pots create extending from their perimeter I'm thinking that the diameter of the pot may also offer its own useful seepage dynamic.

A wider pot makes a bigger pond and the water spreads laterally and below as it seeps trough the terracotta clay. This means that I can plant around the edge and these plants will root and drink both from the sides and below the pot (so long as the soil isn't too compressed or impacted).

In my sandy soil this makes a lot of sense as the deeper you go the more sterile is the 'soil'. Similarly, the shallower the pot the less disturbance and compression there is to the underlying soil structure and the easier it will be to lift up and move around (if I decide to).

I've also learnt that pots with narrow openings -- such as urns and terracotta wine coolers -- are much harder to fill by hand hose than than broad ones. It takes longer to target the lip.

The only challenge is evaporation. As I said in the earlier post, I'm using tiles with a glossy white surface as lids. Light coloured dinner plates would also work.... Now if the seal of the lid is firm enough, the cooling effect of the overhang should work against easy evaporation. And as the seedlings -- planted around the pot -- grow they will serve to shade the terracotta underneath.

If I think that the tiles or the dinner plates aren't solid or thick enough to insulate the pot underneath (or aren't heavy enough to withstand animal investigations) I'll simply glue two tiles or two dinner plates together in order to thicken these lids and make them heavier.

Dinner plates and old tiles are a dime a dozen...and the irony is that the pots I'm buying are cheaper than the terracotta saucers that are made and sold to go with them. And terracotta top -- as the olla literature suggests -- needs to be painted in white in order to reflect the heat of the sun off its surface.

Now if you are into Pique Assiette (broken pottery)mosaic or any mosaic form you'll note the decorative potential offered by these pot lids. You could even set little animal figures atop of them and they'd work as handles!

In reviewing the literature online the arguments in favour of clay pots are strong. Terracotta pitcher irrigation has been shown, in one study,  to save 98.7 percent of water used in sandy loam soils.

That's the kind of  dirty talk  I like.

For small garden plots, sandy soils, limited water resources, dry conditions and lazy gardening this very simple technology ticks a lot of boxes. 

In my setup I'm using a lot of mulch so I'm very subterranium in habit. My major concern -- given the broad lip on my pots -- is evaporation. But today I took the temperature of the water in a couple of pots in full sun and under their lids it remained within a stable range. The mulch atop the soil and the soil itself insulates the pots to create a sort of cellar effect. 

In my garden beds there is  a lot of 'stuff'. Branches. Rolled up newspaper. Cardboard. Nonetheless I fine the pots settle in soon enough among all this detritus and  get to work. However, I'm sure the process of embedding will take  time and as the literature on porous hose irrigation suggests, the soil and plant need time to adapt to any novel hydraulics. 

Unknown is the rate the water will permeate through the terracotta walls. The pots are 'fresh'.  As far as I know they haven't been coated with sealants. When I tested them for any leakage after I plugged the original drainage holes, they sweated the full depth of the water I had poured into them.

Here's a tip: when testing your pots for leakage fill them to the brim as that's your top pressure point.

These pots sweat, I gather, because  gravity forces water through the porous clay walls. Once the water is in the soil,and it's damp,  other processes take over such as osmosis. How far the irrigant will travel from the pot is gonna depend on my soils and other factors I don't as yet know about. But we do know that distance is influenced by components other than sand (such as clay and humus content).

How long it will take any pot to empty is another variable I've yet to  determine. This is, of course, relevant to how often I'd need to top them up. So what's my routine likely to be?

I may also need to relocate some pots and bring them closer together if the wet patches aren't big enough. How far the wet front extends is hard to determine from the literature I've read because there are so many variables. A Leaky hose systems claims that the method will irrigate up to 1.8 metres each side of hose. But some of the terracotta pot research offer very conservative estimates in way of wet front. But pot volume is sure to be  a major determinant as to wetting distance and wetting rate.

This research is interesting:Even small pots can maintain a wet front 60 cms from the pot for a period of 10 days.

Source:

Click on image to enlarge view.

Addendum:Monitoring my pots I estimate -- in our current very warm -- >25 degrees centigrade -- temperatures  -- that they sweat at the rate of 300-500 ml per day. Given that each pot's capacity is 2.5 litres, the formula is one pot full of water will irrigate for 5 days. But then that doesn't mean that it will actually take 5 days to empty in situ or that the wetting effect only lasts 5 days (according to the research cited above).