Building a Mini-wetland

As a native plant gardener in a small southwestern Ontario town, I am blessed to have a half-acre property with a variety of growing conditions. These range from dry, full sun to dry, full shade and from moist, full sun to moist, full shade, and pretty much everything in between. But of course that wasn’t enough, so in 2012 I brought in 40 tons of Manitoulin Island limestone and built an “escarpment”, complete with a waterfall. (This will likely be the subject of a future article – or two). After I retired in 2018, I added a bog garden (see my Dec 2022 article The Boggy, Boggy Dew – the story of Creating a Bog Garden) at the base of the falls. In that article, I lamented that in my impatience to get plants established, I planted a number large, aggressive wetland plants that were overwhelming the delicate bog plants the garden had been designed for.

In 2022 I decided to rectify that problem by building a “wetland” in my back yard – a place I could put all those tall, aggressive spreaders. This is the story of that project.

What is a Wetland?

In Canada (the US has similar definitions) “wetlands are submerged or permeated by water – either permanently or temporarily – and are characterized by plants adapted to saturated soil conditions” (Government of Canada). There are 4 main classifications of wetlands, defined primarily by the source of water. These are Fens and Bogs (defined in my previously mentioned article) and Marshes and Swamps. Marshes and Swamps differ mainly in the vegetation type – Swamps are treed wetlands while Marshes have little or no woody vegetation. Because its size precludes planting trees, I guess my wetland could be considered to be a Marsh.

Where to Start?

As my yard fills up with various flower beds, it is increasingly challenging to find room to create a new feature. I decided to create the wetland near the back of the property, which is about a 6 foot drop below the level at the front. This would allow me to run water via gravity to the wetland during periods of drought.

But, in order to have a large enough area, I had to remove half of the very first flower bed that I built (back in 2005). That, of course, necessitated first creating a new flower bed to move all those plants to. Because of weather conditions, that ended up being a much longer project than anticipated, and delayed the start of the wetland by a year. But in the spring of 2023 I was ready to begin.

My first step was the design. Originally I wanted to incorporate a pond into the wetland, but soon realized that in the small space available this would not be feasible without a lot of engineering. I needed to keep it simple.

In the end, I opted for a two-phase project – a wetland and an adjacent pond. (The pond was supposed to go in this year, but other projects have taken priority so it may not happen till late this fall or some time in 2025.)

Digging the Hole

Then came the “fun” part – digging the hole. There was a lot of dirt to move, and tree roots to work around, but fortunately no stones bigger than a chicken egg (I love my soil!). The hole would be about 170 sq ft and 3’ deep for a total volume of soil of almost 20 cu yards. According to the internet, this weighed somewhere between 10 and 20 tons. (No wonder I had rippling abs by the end of the project!!)

My soil is a sandy loam with excellent drainage, to it was pretty obvious I was going to need to put in some sort of rubber or plastic liner to keep the water from simply draining away. Because I was starting this in the early spring, none of the pond supply places near me had large rolls of pond liner. But a friend came to the rescue – they had an extra piece of plastic tarp used to cover silage on the farm just sitting up in the barn collecting dust, and they graciously donated it to the cause.

Filling in the Hole

Once the liner was in place, I needed a way to make sure the water was distributed through the entire area, but with every option I considered – from “big O” pipe to solid pipe – I ran into the concern of roots plugging the pipe. Even though there would be no tree roots, and I felt that most of the wetland plants wouldn’t reach a meter down with their roots, I couldn’t be sure. So I opted to at least wrap the perforated pipe in a heavy duty landscape fabric.

Then it was simply a matter of putting all the dirt back in the hole and waiting for a few good rainfalls to settle the soil (which it did – a couple times) and then topping it back up.

A few years ago, when a neighbour moved away, I bought several bags of fine peat moss from him that was left over from when he had put in a swimming pool (it had been used, instead of sand, under the pool liner). I spread this about 4-6” deep over the surface and rototilled it in to add some organic matter and water holding capacity to the soil.

Bringing Water

The next step was to bury a 2” pipe from the house to the new wetland. Even though the hole was lined and would hold water, we had a couple of very dry years in a row and I wanted a way to supplement the rain in the event of a drought – without having to drag 150’ of garden hose to the back of the property. Of course, with trees and flowerbeds all through the lawn, I couldn’t lay the pipe in a straight line, though I did dig the trench through one of the flowerbeds rather than go around it.

Laying the pipe was actually one of the hardest parts of the job as it had to be fed under existing pipes and utilities.

Filling With Plants

Digging the plants out of the bog garden and replanting them into the wetland turned out to be a hot and sweaty job – but fortunately a friend dropped in to help. We got everything moved in an afternoon, and there was even room for some new additions.

The moisture loving plants I have in the wetland so far are:

– Spotted Joe Pye Weed (Eutrochium maculatum)

– Sweet Joe Pye Weed (Eutrochium purpureum)

– Water Avens (Geum rivale)

– Southern Blue Flag Iris (Iris virginica)

– Cardinal Flower (Lobelia cardinalis)

– Seedbox (Ludwigia alternifolia)

– Prairie Loosestrife (Lysimachia quadriflora)

– Monkey Flower (Mimulus ringens)

– Royal Fern (Osmundus regalis)

– Ditch Stonecrop (Penthorum sedoides)

– Dark Green Bullrush (Scirpus atrovirens)

– Ohio Goldenrod (Solidago ohioensis)

– Riddell’s Goldenrod (Solidago riddellii)

– Bog Goldenrod (Solidago uliginosa)

– Purple Stemmed Aster (Symphyotrichum puniceum)

– Marsh Fern (Thelypteris palustris)

And a couple of volunteers from nearby gardens:

– Cut-leaved Toothwort (Cardamine concatenata)

– Yellow Jewelweed (Impatiens pallida)

– Black-eyed Susan (Rudbeckia hirta)

Now I just have to wait till they grow and fill in the wetland, and find out if there will be room for some others. In the meantime, it’s back to some of those other projects.