My colleague Ryan asked me to write a blog about swales - actually, he asked me to write a blog about “why swales aren’t necessary and why we should all stop doing them except in clear cases where the design calls for it based on functional need.” Oh, and by the way, Ryan has a half-acre of ridiculous hand dug swales in his food forest - and me, I’ve left a trail of annoying swales over every project I’ve worked on….so here it goes!
My basic contention is that in the Mid-Atlantic climate swales are very rarely necessary, especially given how drastic, costly, and permanent they are. From a design perspective, we should be asking ourselves, “What is the problem or opportunity I am trying to address and what is the most appropriate and efficient way to address it?” We should not be asking ourselves, “Where should I put the swales?!” Unfortunately, that’s still a question I hear all the time, including in my own head.
It’s actually really weird that we are all so obsessed with swales when you think about it. After all, they are basically giant, expensive scars on the earth that make mowing a real pain in the ass. Maybe it’s Geoff Lawton’s fault for pumping us all with heady before and after images of lush, fruit-filled swales in the Australian tropics, all with a charismatic twinkle in his eye. Whatever the reason, the idea of swales has attached itself to the zeitgeist of permaculture like a bunch of burdock burs, planting itself around the world in the process.
So back to design…The main function of a swale is to slow down water sheeting across the landscape and infiltrate it into the soil, making it available to plants when otherwise it would be lost. So when might we want to utilize that function in design? The most common use of swales is in an orchard setting. Here’s the problem - most temperate climate fruit-trees (apples, peaches, cherries) are adapted to semi-arid regions and do not actually require that much water. The 3 inches per month average that we get in the Mid-Atlantic is plenty for most fruit trees once they’re established. What’s more, for some trees like apples, too much water can make them too vigorous, leading to an abundance of vegetative growth at the expense of fruit.
There is one big benefit to swales for fruit trees - they provide a raised-bed that will drain and dry out after heavy rain (fruit trees like to be inundated with water periodically but not stay wet). So if your soil doesn’t drain you could theoretically dig some swales and plant on the berms to achieve better drainage. The problem here is you are not actually solving the underlying problem - you still have that compaction layer below your swales. A cheaper and more effective intervention might be ripping your landscape with a sub-soiler or Yeoman’s Plow on a keyline pattern to simultaneously de-compact, redistribute water, and build soil. So swales in a Mid-Atlantic orchard? Probably not. The reason Geoff Lawton uses them in Australia is because he is growing water-hungry plants in an arid environment that gets huge sporadic rainstorms. When he gets rain he wants to capture every bit of it for his parched system.
So when might swales be appropriate in the Mid-Atlantic? One instance might be in a no-till, non-irrigated vegetable garden. Veggies need a lot of water, and when designed right and combined with deep mulch this system could enable you to grow veggies without any supplemental irrigation. Michael Judd has utilized these types of swales beautifully in his work at Ecologia Design. Another example might be a steep, compacted site with heavy clay soil where subsoiling is inaccessible or impractical. Alternately, I sometimes use swales on a 1% grade to slowly move water off of my site, for example, to get it away from the foundation of a house. Lastly, swales might help for growing water-loving plants like Paw Paws, especially if you can get multiple functions out of them (see Emilie’s Blog “Stacking Functions Part 1 - Paw Paw Perfection”).
When Ryan asked me to write this blog he suggested 500 words or less. But now that I’ve written well over 500 words, I’ve realized the subject is actually a bit complicated. I guess that’s because swales, just like good design, are all about your goals, your context, and the unique and evolving characteristics of your site.