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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. 

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 now that distance is determined 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 whats' 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.


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Comment by Dave Riley on November 13, 2015 at 9:09

Thanks Elaine I will keep the roots in I work out my preferred mound size. 

As for Northcote Pottery's cottaSEAL  collection -- the terracotta pots I referred to are in their Italian collection --and are obviously imported.  Any one shopping for these pots should, if worried,  contact the company and ask. As it is, if you are buying pots to bury, just get a couple; take them home; seal the bottom (I use grout) and fill them with water and wait to see if they sweat water. Also check the mouth with a dinner plate as 23cm is not in my direct experience.It will surely cover as a lid -- but you want to be able to reach down and easily remove it. So you need enough lip to grab onto. You can simply slide these lids off -- as I used to -- with an adapted walking stick but if there is growth close in the plates get gaged. 

Assuming the figures in the original post I originally placed my pots 1.3-1.5 metres apart because I had to have 'a plan'. But that was on flat earth and the layout always bugged me, primarily because you'd assume that water egress went down and out like a large droplet, especially in sandy soil. 

With mounds you more or less build a soil coating around the pot. Even if the mound is half a metre high these pots are 18 cm deep. So the soil space is readily wetted without sections  being so much dry as the pot is like the nucleus in a cell.

Imagine that as a guide: the mound as a cell with an activated core and contained by a perimeter of air shaped by contour. It's a living thing in itself and you are its steward.Everything else aside,it's much easier to treat this thing -- dirt mound+pot --  as a separate ongoing project from all the other mounds. It becomes much easier to recognise what needs to be done.  

"This mound looks OK. That one's a bit daggy. These others could do with a weed pull or two...and they could all do with more mulch..."

A lot of DIY clay pot literature chases after depth but that's really not essential as that's where the water will go anyway -- down. It's the horizontal you want to fret over and the challenge is to keep the moisture  hanging about where it can be accessed by the plant roots. Indeed it is easy to be schematic about what happens to the moisture after gravity drives it out of the pot.

But since water molecules attract one another and can rise up as much as trickle down -- as per wicking principles -- the bottom  mulch 'moat' ringing the mound and capturing any run off and condensing moisture (such as from dew) -- is a supplementary built-in mechanism.

I learnt a lot from using the Leeaky Hose system. That didn't work so well in my sand as the moisture fell away too quickly. The problem was that Leeaky delivers water below ground at  2 litres per metre per hour...and then stops as soon as you turn off the tap (although capillary take up is assumed). The clay pots deliver  2.5 litres over  3 days . So what's not to like?

And always with Leeaky I'd forget to turn off the tap and run the system for far too long...or not long enough.  But then, as an indicator of potential, Leeaky  supposedly irrigates up to 1.8 metres each side of the hose. That's using light water pressure of a slightly turned on tap  rather than the gravity the pots rely on to work.

But essentially the method is the same : watering under ground under light slow pressure.

Comment by Elaine de Saxe on November 13, 2015 at 4:41

Sounds like you've hit the jackpot with gardening in your sand, Dave! I'd always leave roots in the ground, just cut off the plants when they are finished. Anything we can do to keep the microbes happy and producing is free fertiliser - if we pull out the roots, there goes their home and hearth.

Comment by Dave Riley on November 13, 2015 at 3:57

As an addendum, I'm thinking that the optimum mound size is approximately 

  • a square base of 1.3 x 1.3 metres
  • a convex height of 0.5 metres
  • irrigated by a 2.5 litre pot
  • on an incline of  35-40 degrees

Most of my mounds are smaller (indeed much smaller in many cases) than that and it takes guts to build 'em so big so I've been hesitant. But in my soil that's the hypothetical size I'll test over Summer. My assumption is that size is related to heat retention and drying out rate. So I;'ll bea sking for problems.

But in terms of management that scale has a keen logic and I'm assuming the pot can 'feed' that soil volume. That is also a mound carpeted in grass clipping mulch with a shallow peak. 

I've been planting out my mounds  willy nilly but it is clear that polyculture with mounds does need practical 'rules' and not all plants cohabit well with one another.

Zucchini will overgrow other plants. Potato is a hard harvest in the same mound as other annuals. Spring onions and root veg prefer to be planted around the pot rim/at the top of the mound. Tomatoes are a challenge to contain.

At, or towards, the base I'm experimenting with planting pigface, canna, dog bane, Brazil  spinach, Warrigal Greens, sunflower and Pigeon Peas. In some hollows I have Qld arrowroot and taro. The problem is once the plants take off I have a jungle effect underway and it's every plant for itself. So it is harder to imagine what is happening underneath it all in the soil.

So I have this immense mix of plantings tumbling hither and yon as I try to decipher some logic. 

I've harvested some spuds from a few smaller mounds and the harvest has not been great this year when last year it was ab fab. Why that is I'm not sure, but the soil was a good loam with worm activity. And it was coolish -- not dry and hot. 

Once plants grow and shade the knolls (and I do consciously close plant), I don't get much in the way of weeds so aside from refilling the pots and harvesting, the maintenance is negligible. I've seeded new mounds with manure, blood and bone and lime. As well, when available I've dug in chopped up help store water and reduce hydrophobia in soils.

PIGFACE ASIDE: I'm thrilled to now have so much pigface (Carpobrotus glaucescens) coming on as I can now really get serious about deploying it as a 'wetting' agent.Easy to grow. Just snap off a bit and replant it. I'm experimenting with growing other plants among the pigfaces' succulent leaves --sort of like a living mulch. When it takes off, it's like covering the ground with a green mesh...but it isn't weedy. easily controlled. Looks great. Even edible and with healing properties akin to aloe vera. It's a great coloniser of new land and ideal for filling up gaps.So inside a few of my mounds -- like Pharaoh's tomb -- I have buried chopped pigface. I don't know how much chopping is required for best effect but with practice I'll be able to offer a ruling. Unfortunately, the southern species of pigface, Carpobrotus rossii, doesn't thrive in my patch. I grow it but it hasn't spread. My C.glaucescens has never flowered nor has it produced fruits. Whereas C.rossi keenly flowers and fruits! Go figure. 

Aside from my 'wild patch' all that remains of 'flat earth' is a couple of spots while I wait out growth and harvest before I convert to a new contour. That's an easy business of digging down and making a moat around the mound, then filling that with paper and mulches.

Nonetheless, I have such a jungle effect going that I quickly lose control...and compared to 'flat earth' --well, I'm never going back to that. At the moment, these last few weeks for instance, my plants are doing much better than those in the school garden with its imported purchased soils and every other day hand watering.

At the moment I'm fretting over harvest and trying to decide what I'll do with each mound once I've picked my supply of produce. Do I uproot the plants or do I crop them to soil level and replant in between the dead roots? You can imagine how destructive uprooting is to contour ...and the biology active and attached to the plant roots.

The mound gardening tradition in Melanesia, Polynesia and the Americas is to rebuild the mounds every year. My preference, instead -- my hypothesis -- is to 'top up' the mounds every year by shovelling the run off and composted mulch from the moats and valleys at the base back up the hills. But then I'm open to the notion that mounds are transitory and can be remodelled every year. Indeed, it is a very plastic way to garden. 

Of note is that cane toads hate the vegetation and the landscape...and my one hesitancy is that I'm sure to get snakes, at some stage, among all this growth (what with the fallout from having chooks...)And the darn dogs poop on the paths as 'off road' is too challenging to negotiate.

But hey! it's magical! Especially when the dinner plates are drowned in growth and the verdancy takes over. I can't harvest all that 'ripens' , because there is too much of it sometimes, so a sort of sustaining and reseeding logic kicks in. My challenge is to navigate and know where what I want to harvest each day is located. So if I'm not among it all with my trusty hose I'm not taking inventory.

I'm thinking of adding stepping stones to some places to facilitate transit.If I can get the right size stones I can move them around as needed rather than trundle along the valleys as I do now, every now and then -- as though I'm Jack's giant mumbling 'fee fi fo fum'. 

As I've said before, my grandfather had a tiered veg garden up the side of a hill and you got around it horizontally on stepping stones and you climbed it on a cement strair way. As kids it was an enchanted place to visit...berry bushes and tomatoes were things you stepped over, not around.

I've had to make tool adjustments as I no longer take the wheel barrow to boldly go where it has not gone before. I now use buckets and light trolleys to carry stuff, such as mulch, about the garden.

To complicate logistics I have vines a'plenty. The chokoes have taken off again. Mouse melons are under way and while the pole beans are desultory I have a few types of yams shooting skywards.

So my aerial lines are being colonised again. And when the pigeon peas grow up and the frangipanis develop over Summer, I'm wondering if I'll be able to find the garden at all..or that, once outback, I'll get lost in the greenery.

And this is all happening on sand while keeping to  a very limited water budget. None of this turning on the sprinkler or irrigation system.No set it and forget it habits. It's all hand hosing and clay pots... and aside from a few short lived perennial plants, the vegetation is comprised of annuals. Indeed edible trees don't thrive in my patch.

Even the Moringa struggles! Citrus does OK. But every other edible tree I've planted has failed to thrive..aside from mulberries. I have planted out plenty of Katuk as I've skilled up handling that bush. But I've given up on pawpaw and figs...

So I'm very much gardening shallow.

KATUK ASIDE: Love katuk heaps and have finally mastered the growing thereof. Just follow a few simple rules:

  • take cuttings at every opportunity. Pot them up and bring them on in the shade.It isn't keen about sunshine. Cuttings are easy to strike.
  • plant out and grow katuk in the shade. I can grow it shaded from the western sun so I'm developing a hedge.
  • harvest by cutting the branches NOT by stripping the leaves.

Katuk goes with everything. Soup. Stews. Salads. Salsas.Stir fries. It even beats spinach on some nutritional aspects. Katuk: 49% protein, 18% fiber, vitamins A, B & C, potassium 2.77% (more than bananas at 1.48%); calcium 2.77% (dried skim milk is less than half that at 1.3%); phosphorus .61% (dried soybeans are at .55%); magnesium .55%; and even enough iron to mention. See overview of Katuk HERE. But you need to use it sparingly if you are a green smoothie junkie because it contains Papaverine and other fascinating compounds you don't want to over indulge in... But hey! It will help you lactate if you are into breast feeding!

Comment by Christa on November 12, 2015 at 18:53

This is what I found   [Northcote Pottery’s cottaSEAL collection features a range of traditional and versatile terracotta pottery. Pre-treated with water resistant sealant to prevent moisture absorption, cottaSEAL pots help you save water, time, and plant stress]   

Comment by Dave Riley on November 12, 2015 at 16:42

HOSE:I originally bought mine on special without fitting ends so I'm only talking about the hose.But what a great day it was when I started with kinkless. Elsewhere they're over $100!

So you'd need to ask about the end bits.

POTS:I know the Northcote Pottery well as that 'hood is my old stamping ground and there were a few really big holes on the ground for digging clay just north of Melbourne.It used to be on Separation Street.  I lived over the road from one of them.

Deep holes and some of them were simply turned into tips for garbage...or built shopping centres on top of them. One is now the Ray Bramham Gardens

As for sealant -- we'd need to ask the pottery itself.

Unfortunately the Ipswich Pottery closed down some years back...but they did a great clay pot. 

Masters clay pots were/are imported from Italy.

Comment by Christa on November 12, 2015 at 16:06

Dave, just check to see if some of the Northcote pots contain some sealant, or is cottaseal the colour?  

Comment by Elaine de Saxe on November 12, 2015 at 14:05

I almost wish I had mounds … Are the hose fitting super strong? I am thinking about the ones with metal bands fitted to plastic click-ends. It's a well-known brand I've forgotten the name. My plastic ends which are a good brand, are forever blowing off so I figured I'd get the ones which were really secure. But as yet I've not really looked into the situation.

Comment by Dave Riley on November 12, 2015 at 11:45

Just on kinkless hoses: this model (my choice) is good value --and with free delivery it beats hardware store shopping.

As for pots.  Masters sell 19 cm pots for $2.20 each (but a 21cm diameter is preferable and more useful ++ because of the greater volume).Masters usually does sell 21cm (but I started my collection with 19cm diameter pots). 25cm is too broad for easy management and any lid will be hard to lift on and off as a standard dinner plate is 27 cm wide which will only give you less than 1 cm lip to grasp.

Second hand wine coolers work very well (bought from op shops -- but don't pay more than $3/each) --covered with cup saucers.

I see where Bunnings has a 23 cm pot (made by Northcote) for $4.48...and that diameter should work OK buried and lidded.The bigger the pot, the greater the volume capacity.But you also want easy lift off especially if you are to fill many 21 cm is still the sweet spot diameter  based on my experience.

So when shopping take along a tape measure...

And use dinner plates as lids rather than tiles or stones. Aside from the shine and price, the plates settle snugly over the lip and are light to lift and move.They are like frisbies. Passing animals will knock your pot lids and crows are smart enough to flip them --so snug matters.And an open pot is a cane toad's bath time.

If you are into daintiness, there are a lot of stunning dinner plates you can use in your garden decor. If you use clay pot saucers as lids, you can mosaic or paint these to dress them up -- but they are cumbersome lifts. However, if you attached a figurine as a handle -- a cute wee garden gnome for instance -- you are adding much value to your irrigating experience. 

Comment by Dave Riley on November 12, 2015 at 2:55


It's coming together...

After relying on terracotta clay pots for irrigation these past few years I've become a master at the craft. 

The recent shift to gardening with mounds has made running my clay pot system so much more efficient.I use fewer pots so the refill numbers have fallen. The one-pot-per-mound protocol  ensures I can monitor how effective the irrigating is as each mound serves as a self contained watering unit.

I'm still experimenting with mound size (height + circumference :  depending on soil quality) relative to moisture reach but it is very clear to me that the 'best' use of clay pot irrigation is using these sculpted knolls. 

My experience suggests a few lessons worth sharing.

  • Pot mouth: Much clay pot literature relies on variations of the Olla design (pictured) with its narrow lip. But how do you fill these urns with water? With my  preferred plant pot size of around 21cm circumferences, all I need do is remove the lids one after the other then fill them with a garden hose. I can stand at some distance from the pots to do this. I can stand in the one spot and fill a succession of pots in reach of the hose spray.Squirt. Squirt. Squirt.
  • Gravity: Locating the pot at the apex of the mound not only draws the pot mouth closer to the hose and yourself (by dint of height above sea level), but vegetation -- in the main -- tends to fall away down the mound slope. This encourages a clearer 'shot' at filling the clay pots as they tend to be more exposed than if they were at flat ground level.
  • Lids: Much as I'm keen to experiment, I've not found a 'lid' more suitable for covering the pot mouth than a good ole (preferably stoneware) white dinner plate. They are a snug fit, cheap to buy at Op shops, stand out among the vegetation and are reflective of the sun. When gardening I use them as wee tables to hold seedling pots when I'm planting out, or to cradle weeds I've pulled.
  • Spray gun: For all my hand watering needs I've found a Brass Spray Gun (for around $25: pictured)  to be the best tool for the clay pot job. This type of nozzle gives you great directional and force control without wasting water.
  • Mosquitoes: Any standing water is sure to attract mosquito larvae which in turn become pupae, etc. Mosquito larvae, commonly called "wigglers," live in water from 4 to 14 days depending on water temperature. Pupa live from 1 to 4 days, depending upon species and temperature....So if you do your sums it makes biological control sense to let your pots dry out before refilling them. Not all pots will carry mosies' brood but since infestation will occur the best protocol is to  only fill the pots when you think the plants need watering. That's a subjective art. Look a the plants in the pot's arc of irrigation. Feel the soil at various distances from the buried pot. A pot will take 3-5 days to empty its 2.5 litre volume --depending on the weather. So if you manage your habits well enough, the pots can serve as keen mosquito traps.
  • Removing Pots: Once established, many plants won't require the clay pots for irrigation. Perennials, trees, even potatoes...most times  can survive without a constant water supply. In such cases you can remove the pot and use it elsewhere. But here's the trick: to the moulded hole the pot was in, throw in some paper, mulches,twigs,manures, etc and treat it as a 'honey or fertility hole'  which you can later engorge when  hand watering.
  • Getting about with a hose: When I hand water, I 'm usually visiting every part of my garden. That requires me to negotiate a maze of pathways in order to get from A to B. Obviously a 'kinkless' hose is gonna be worth the purchase (not than any hose is absolutely kinkless). But turning corners with a hose in hand can drag it across the garden beds and damage plants. I've found that the best way to handle these manoevres is to ram in bollards at each turning and drag the hose around these. While I use old metal tubes for this (eg: you could also use star posts), my preferred bollard material is fibreglass tent poles (pictured).The old family tent may have many uses, but these poles are not only durable in all weathers, they flex not only with the drag of the hose, but when you are close-cornering with a wheelbarrow. That means you can make your paths narrower and allow more space for growing stuff.
  • Impermeable Pots: A certain percentage of the clay plant pots you'll buy will be impermeable.While terracotta clay should be porous, some firings or grog mixes sabotage that attribute and the pot will refuse to empty itself through its walls via gravity.Planted in the garden that pot is still going to be useful as it will act as a condensor and coolant in the soil. It happens too that some pots are very slow to empty. But if you think you have a dud, you can remove the plug you inserted and deploy the pot for what it was made for. I've found that maybe up to 15-20% of the clay pots I've bought are impermeable. Since it's  no good taking them back and complaining you'll have to live with it and accept that dud pots are part of the mix.
  • A little splashing helps: During hot or dry weather, or when water volumes in the pots are low, it pays to hand water the garden to keep the circuit functioning.Freshly planted seedlings always need attention anyway.I find that with my very sandy soil I need to hand water often as what 'loam' I've got is very friable and doesn't hold much moisture. Even a light splashing of water on the soil/mulch, keeps the pots in irrigation mode as water begets water. The pots irrigate by dint of (a) gravity (b) chemistry (c) conductivity...and other science of soil factors. Indeed, at times of heavy rains the water flow will reverse and the pots will begin to fill from moisture in the soil. So it would be presumptuous to assume that 'a' pot is a magic bullet. You need to develop  an ongoing relationship with your soil and its vegetation and adjust your hand watering and irrigation  habits accordingly. Judicious hand watering, in my experience, extends the dampness arc the pots service. This is particularly useful as  the strength of the gravity driver lessens with the fall in pot volume. Without a helping splash about, permeation can become sluggish. 


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