Garden Swale

Bog-gardening, and related wetland enhancement seems to be my theme of the week (or two). A swale is technically a "low-lying stretch of land" or a "marshy heavily vegetated depression." Swale gardens are becoming a bit of a trend--in my world anyways!

The City of North Van has started recreating or enhancing swales in parks around town, where groundwater naturally surfaces and defies our attempts to grow green lawns everywhere.

This swale on Grand Boulevard was enhanced a few years ago. Crews laid stone, starting here in a catchment pond, and following the bottom of the swale to facilitate water flow and drainage. The banks were planted with indigenous plants, which have filled out very well. Up close, wild roses and rushes, oceanspray and snowberry are naturally beautiful and a sanctuary for wildlife.

Local Homo sapien friends, Liz n' Len, decided they needed a Garden Swale in their back garden when their former lawn turned into a bog every spring. Here's Len (below), with one foot in the swale and one on the bank, to show how deep it is. Very well demonstrated, Len. They basically dug a trench and lined it with drainage material to contain and direct the water that otherwise drooled randomly around the garden. (Same concept as the Boulevard swale, right.)








Then Liz n' Len planted the banks with a selection of indigenous and garden plants, including moisture-loving blueberries. The enormous plant to Len's right is the native Goat'sbeard (Aruncus dioicus) which also obviously likes wet feet.

And they built a little bridge, which is a little bit like having a theme park in your back yard. Too much fun. Thanks for participating Len. Now get back to work.

So this brings me to Sheena and Terry's garden, where a Garden Swale is just waiting to happen.
Here is Phase One--two new garden beds installed last year, in a boggy corner formerly inhabited by a crop of horsetail (Equisetum):






Years ago, Sheena and Terry discovered that a sub-surface creek runs across this section of their property--just close enough to the surface to make a lawn impossible. At the time, a black plastic liner and gravel was the solution--we will forgive them for this, because a lot of things like that happened in the 1970s...

I can't tell you how happy I am that we have, in recent years, begun to reclaim what I call the "gravel pit." When we installed these two beds, the soil soaked up water like a sponge--perfect for the clumps of yellow flag iris, white Japanese iris, indigenous rushes (collected onsite) and various other grasses planted so far. The beds were also perfect for the horsetail, which promptly abandoned all gravel surfaces and came up only in the nice new soil. (Horsetail is intelligent flora--a sometimes frightening thing to witness.)

But, since you can't get rid of horsetail (it's been around since the days of the dinosaurs) my original thought was to work it into the design [insane laughter]--and the fact that it decided to relocate itself to the beds made it look more...intentional. I figure, the rest of the plants in the design just have to be taller than the horsetail, and we could learn to appreciate its soft verdant green as a groundcover.

Here's a picture of another garden's boggy area, where horsetail is allowed to grow (because no one goes there anyways).



One day, the Gunnera, which looks like a rhubarb at the moment, will be huge. Same concept: the horsetail could be considered a feathery green groundcover. Why not?

Nevertheless, Terry has an ongoing (primordial) and personal vendetta against horsetail and insists on weeding it from the beds, even though I'm insisting that it is integral to the design. Even though it re-emerges two hours later. Terry isn't here to defend himself, so this is really fun.

Meanwhile, the corridor between the two new beds still holds standing water so we are planning to dig a shallow trench, just deep enough to direct the water along its way...









...and fill the trench with a stream-like assemblage of river-rock, similar to the picture below...





I built this faux-stream-bed elsewhere about nine years ago (!) with three sizes of river rock, laying the largest stones first, then the medium stones, and finally packing small stones in the "eddies." (One must think like water, sensei.) This is fussy, because the creek bed is a garden feature. If you are just throwing rubble in a trench for drainage, so be it. But I have seen "dry creek beds" that look, unfortunately, like someone threw rubble in a trench.

So, for the next phases of Sheena and Terry's Garden Swale, we will be creating both a garden feature and a functioning swale that helps collect and drain groundwater. It will follow the water's path that-away across the gravel pit, connecting the space with other garden beds we've created along the way. The plants seem to really like the combination of the moisture and the retained heat in the gravel. So even I can learn to like gravel...in moderation.


















Learning to love it. Equisetum.
"Equisetum species have an affinity for gold in solution, and they concentrate it more than most plants, so they have been used in bioassays for the metal." Pojar and MacKinnon, Plants of Coastal British Columbia