Making a swale

I’ve made a couple of new swales recently and started a third, so thought I’d document the process.

I had a lot of asparagus to plant out and wanted to put them on a swale mound. Here’s the first swale. It’s about a metre and a half long, 40 cm wide and 30 cm deep:

The asparagus are a bit hard to see. I’ve planted dandelions in between them, which are easier to see (the flat rosettes). The day after I took the photo the dandelions disappeared, courtesy of the rabbits. I put wire over them and they grew back good as new. Can’t keep a good dandelion down! There’s a variegated mint doing well at the far right. Rabbits don’t like mint, it seems.

At the outer edge of the swale mound there are four Strawberry Guava plants. They should grow into shrubs about a metre high with tangy red berries.

The second swale is about the same size and sits at the lower edge of a gravel path. It fills from water running off the path. I’ve planted more guavas at the base, Cherry Guava this time. They’ll get a bit taller, but I’ll keep them to a metre or so. In between them and on top of the mound are a couple of oregano plants. They should sucker and spread along the swale, maybe even grow down into it.  On the far right is a Buddleia—a Butterfly Bush. Circles of wire surround everything until it’s established. Pesky rabbits again!

I’ve just finished the third swale. Like the others, it’s on a slope. I had just a few asparagus plants left and wanted to get them planted before they go dormant for the winter.

Since these are small swales it’s not really necessary to mark out the contour; trial and error is pretty much OK. First job is to dig out the ditch by hand and rake the soil into a mound on the lower side. Then I cover the mound with cut branches sloping away from the swale. I’ve used meleleuca here because it’s no good for firewood as it’s too soft, and it rots easily, so will add carbon to the soil fairly rapidly:

Then I deepen the swale and rake the soil over the sticks. If I have extra soil I’ll add it, too. I could go on adding sticks and soil, making the mound higher and higher, but while sticks are plentiful around here, soil is not (unless I want holes everywhere). The sticks are supposed to deter the rabbits and blackbirds from digging up the soil on the mound. It sometimes works:

You can see water in the swale. I fill it frequently as I’m going, just to check the levels. Mostly the ends will be the spots that need adjustment, building them up so that water doesn’t flow out. It’s looking pretty good:

Finally, I cover the swale with mulch. I’ve used casuarina needles here, because I have a huge supply:

It would be ideal to be able to broadcast seed into the mound at this point. Something like clover or vetch—something that would hold the soil in place and maybe provide nitrogen, but the rabbits would eat the seedlings down in a flash.

I might use yarrow. It spreads by underground rhizomes and the rabbits usually don’t touch it*. I can dig up a few clumps and plant them out, protected with wire, till they establish. I’ll put the remainder of the asparagus in later this week and that will be the end of about 2 dozen plants I grew from seed last year.

This swale is a bit over 2 metres long and I estimate that it will hold about 80-100 litres of water when full. I won’t put any chook poo compost on it until the asparagus spears are starting to appear in spring. They won’t be big enough to eat this year but my older plants are in their third year of harvesting so I can afford to wait.

* I once found a dead rabbit with a wisp of yarrow poking out of its mouth. I can’t believe that’s what killed it, but it would be nice to think I’m growing something that would. They do eat down the flowering stems though, but don’t seem to browse the leafy rosettes; not excessively enough to notice anyway. It annoys me because the flowers are rather attractive en masse: