Permaculture uses several techniques to deal with a drylands (i.e. desert or sub-desert) climates. We’ll talk about some of these techniques below.
So let’s think about what properties drylands have:
- Dry – lack of rainfall and general moisture, results in less and lower plant growth.
- Delicate – because of the lesser plant growth, any disturbance will be take a long time to correct
- High in nutrients – Nothing rots, it mummifies and preserves, though desert soils generally lack nitrogen
- Easy to create – improper management of large herbivores can create drylands
- Large annual rainfall events – many times, large rain rainstorms cluster, then no rain for the rest of the year
Most techniques for dealing with drylands climates will have something to do with preventing evaporation. Since it is so dry, water will want to evaporate to be in the air. Our job here is to reduce this evaporation to a manageable level so that we’re not losing lots of water and getting no benefit.
We also must be able to handle the large rain volumes when they do come. Drylands have the unique feature where most of the annual water comes in a few large rainfall events. Because of the lack of vegetation to hold onto this water, it can easily create a flood. Then quickly the water is gone, and it’s dry again.
We aim to smooth out this “feast or famine” cycle by buffering the water surge so that we always have a supply of water. We don’t want to choose between drowning or dying of thirst!
Floods are no fun!
So what we need to do is make best use of the water we get, store what we can, and prevent it from leaving too quickly. A common phrase for water management is “slow it, spread it, sink it“.
- Slow it down – slower water movement means less erosion
- Spread it out – the more water is spread out, the less destructive force it has
- Sink it in – water in the ground move much slower, and is much less prone to evaporation from sun and wind
To do this, we make use of earthworks techniques, positional (where an element is in relation to other elements) and temporal (time-based) building and management techniques, as well as taking advantage of the normal physical properties of certain elements.
Floods are a big waste, both of water and the potential energy (and plants) they represent. You don’t want erosion, or landslip, and for sure you don’t want to lose all that water.
Techniques – our permaculture toolbox!
- Swales – earthwork ditch on contour, a tree-growing system
- Shade – reduces evaporation
- Cooling airflow – plants grow better, people are happier 😉
- Berms – Blocking wind, food growing microclimates
- Thermal mass – dirt, stone, or water for storage of cool air
- Home design
- Wet pots – original swamp cooling
- Natural airflow – heat wants to go up, let it pull cool air into the house
- Solar orientation
- Zai farming – African deep garden pits with manure
This list is certainly not all-inclusive, and there are more techniques that can solve specific problems. In dry Australia (where it was invented), keyline design (and keyline plowing) has done very well to make use of the little water they get.
Sidenote: There are many ways of handling heavy rains.You may be thinking ponds or tanks are the way to go, but that may not be the best move. Some other examples are dams/ponds, net & pan, fishscale checkdams, gabion baskets, and keyline plowing as I said above. What technique you use depends on the local conditions and your resources.
One technique to handle large amounts of water quickly is by using a (series of) swales.
Definition: A swale is a flat bottom ditch on contour, with a soft dirt mound downhill. Size varies, but there are some guiding ratios to get right. They should also always be planted with trees AND other cover crops to keep the soft soil mound from eroding.
Even though the above swale is not perfect, it still works well. The sides should be sloped at a gentle 1:2 ratio, and it should either be wider or shallower, preferably wider.
This swale catches lots of water that would otherwise run off as waste.
If you have heard anything about permaculture, you’re probably heard about swales. They work quite well in drylands, but they’re not always the best solution to every problem.
How a swale works:
- Stops water from rushing downhill
- Water spreads along swale, filling up level all along the swale
- When stilled, water slowly soaks into the swale mound
- Stored in the ground, water doesn’t evaporate by hot sun and drying wind
- Trees planted in the swale mound can have better growth from this supply of water
- When full, a (properly designed) swale will gently overflow from a sill, preventing erosion.
- The overflow sill can drop into a swale further downhill and start the cycle again, so much the better
WARING!!! One thing to know is that they MUST be planted with trees. Swales are a tree growing system. Installing swales without trees is asking for a landslide. It’s also a very good idea to plant some other smaller bushes and herbaceous plants to anchor the swale mound.
Swale implementation tips
It’s a GREAT idea to put a swale in just before the rainy season starts. That way the plants can immediately take root and start holding that loose soil in place.
We don’t want the wind blowing it away!
You: But I don’t have 40 acres, I have a backyard in the city! How do I put swales in?
Ok, grasshopper, you can still use the technique. Maybe you don’t want to put in a 2o-foot wide swale?
Just downsize it to what you need!
Put in a swale that’s only 1 shovel wide. That pretty easy to dig and should handle quite a bit of water.
You can integrate it with a small pond for frogs and toads. This is great for pest control and mimics a natural setting in your backyard.
Shade can reduce the evaporation by lowering the temperature of plants, water and soil. Since plants use water transpiration to cool themselves, like in the way people sweat, shading means they don’t have to work as hard to pump water. This mean they can do more growing and producing food.
I suggest shade with the following:
- Overhead: 50%
- East: 0-20%
- South: 50%
- West/southwest: 70%
The western side will be heaviest shaded, because that’s where the afternoon summer sun is. This is also the reason overhead shade is next heaviest, because the summer sun is so high in the sky.
You can create shade with shade cloth, or naturally with trees. Trees are a good choice because their transpiration can cool you down too.
Mulch also can create shade, at least to shade the ground from direct sun. This will help keep the soil from drying out so quickly, though it may not help shade you unless you’re an earthworm!
I like wood chips for this. They don’t rot down into a stinking mess, they contribute to soil health and moisture conservation, they don’t really compress, and they’re easy to move for planting. They really soak up water, then release it as the soil dries out.
Sidenote: And I mean wood chips. From 1/4″ to 4″ size. Not sawdust, not sticks or branches. I get mine from a local sawmill that grinds up the excess cutoff log pieces into chips. You may be able to get curbside chips delivery from tree trimming services, sometime for free!
I have my fruit trees mulched in a sunken basin with at least 8 inches of wood chips. Even in the hot mid-90’s, I only have to water every few weeks, by just filling the basin up and letting it soak in. Wood chips work great!
This post series will be continued in Part 2.
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Jed & The Crew at TPL