About 7 years ago we planted 3 rows of fruittrees ( top row of cheery, followed by 2 of apple) on a very gentle south-facing slope. Now that I know more, it sounds like a great place for contour swales. Is it even possible to add that now? I guess I would need to make sure that any digging was outside the root zone, and that the excavated material didn't bury the tree deeper, right?
I would also like to convert the area into a food forest. Is there a best way to do this? Is it better to scrape off the grass, or to smother it with cardboard and layer on top of it?
It is hard to do after the trees are planted, especially because they probably are not planted on contour.
Swales are not an essential design feature. They are a useful technique to capture the water instead of letting it runoff. In my experience, they can be extremely valuable when you establish trees and there is not much rain after they get planted. That being said, if your trees have been there for 7 years, they have deep roots and can survive droughts to a certain extent.
Depending on the layout of the land, you could swale up hill from the orchard, which would probably make water travel underground towards your orchard, and you could build a swale downhill from the orchard to capture the surface water that goes through the orchard.
Again, swales are one of the techniques to capture water. There are other techniques that may be more appropriate to your situation.
If you do decide that building swales in the orchard is essential, not impacting the roots is a big thing.
Here is an interesting (and maybe relevant) video that covers the pros and cons of swales.
Basins sometimes fit between established trees better than swales. They are just depressed areas in the landscape, with extra soil put on the downhill side. They collect runoff and organic material and might be a good place to plant some perennial food plants between the trees.
If you have a particular need to intercept flowing water among the trees, rather than upslope, you might try 'swales' consisting of fallen trees laid on contour; peg them in place if it's steep enough to worry about them moving. This would minimize the soil disturbance; you'd probably still need to do a bit, to get the 'swale bottom' properly level, but pretty slight.
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