Creating a Bog Garden
I am fortunate, as a native plant gardener, to have a ½ acre property with dry shade, dry sun, moist shade, moist sun, and everything in between. Combine this with rich, sandy-loam soil and, for the most part, if I accidentally drop a plant on the ground, it will take root and grow (at least that’s what my friends claim). This has allowed me to create gardens of deep-shade forest perennials and tall grass prairie, of moisture loving ferns and drought tolerant grasses.
Escarpment and Waterfall
In 2012, I decided to take advantage of a slope in my yard to build my “escarpment”, complete with a small pond and a disappearing waterfall. This has provided even more habitat choices where I can now grow things like smooth cliffbrake (Pellaea glabella) – a fern that lives on limestone cliff faces. The pond and waterfalls provide the moisture needed for things like the semiaquatic blue flag iris (Iris versicolor), bog bean (Menyanthes trifoliata) and large leaved arrowhead (Sagittaria latifolia). I even planted some Green Dragon (Arisaema dracontium) this past spring in a pocket of moist soil at the edge of the falls.
Despite all this variety, I still felt there was something missing so in October of 2019 I decided to build a bog garden where I could grow things like orchids, pitcher plants, sundews and other acidic-moisture loving species that grow in the bogs and wet areas of Ontario. Today’s article is about how I built it and some of the lessons I learned along the way.
What is a Bog?
But first, what is a bog (and thus a bog garden). A bog is one of four main types of wetland – bog, fen, marsh, and swamp. Of these, bogs and fens consist of saturated nutrient-poor acidic bodies primarily made up of sphagnum (peat) mosses and peaty soils and very little flow of water. Marshes and swamps, on the other hand, tend to be alkaline with a constant change of water through the system. The main difference between a bog and a fen is that bogs are fed solely by rainfall, whereas a fen receives water through groundwater and surface water, resulting in a slightly less acidic environment (by this definition, my “bog” garden is actually more akin to a fen as there is a constant exchange of “groundwater” because of the way it is built.) As a consequence, fens typically have a greater diversity of vegetation, which may include more in the way of shrubs and trees.
In addition to sphagnum moss, the vegetation in a bog consists of heaths (Erica spp.), sedges (Carex spp.) and grasses such as cotton grass (Eriphorum spp.). Bogs also are the home of carnivorous plants such as pitcher plant (Sarracenia purpurea in our region) and sundews (Drosera spp.). These plants have resorted to capturing and dissolving insects for the nitrogen and other nutrients the acidic soils lack. Bogs are also a place where you can find a variety of orchids (Platanthera spp., Spiranthes spp., Cypripedium spp. and several others). Most of these plants are low growing, exotic looking, and can add a beautiful splash of colour to your yard.
Locating the Bog
The first steps to building my bog garden, as with all my projects, was to find the most suitable location. I needed an area that I could keep constantly wet. At first I thought I might be able to build it at the outflow from the downspout of my house, similar to a rain garden. But a rain garden is usually designed with plants that can tolerate drying out between rainfall events but won’t easily drown if submerged for short periods. Ideally, a bog garden will stay continuously wet – in fact some bog plants will quickly die if they dry out. I then wondered whether I could use my existing water feature by building a bog at the base of the waterfalls.
At the base of the falls is a pit approximately 3’ deep and 10’ across, lined with a rubber pond liner and filled with rocks (large ones at the bottom, smaller near the top). A large diameter pipe holds the circulating pump that takes the water up to a small pond at the top where it tumbles back down to the pit. Originally, I had to top up the reservoir at least once a month in the summer because of splash and evaporation, but I have since tied in the downspouts from the house and I now only top it up in prolonged periods of drought. Since this reservoir is almost always full of water, it seemed the perfect spot to put my bog.
Building the Bog – STAGE 1
The first thing I needed to do was excavate a hole. Given the substrate consisted of pure river rock, this was not as easy digging as it would have been in soil. But I soon discovered (after a heavy rain brought the water level in the reservoir up to the top) that digging rocks in a flooded area was actually easier than digging them when it was dry. It was just harder to tell how far down I was going. I just kept digging till the water in the hole seemed to be at least 18” deep throughout. Once I had the hole deep enough, I then placed a rubber pond liner into the new pit and proceeded to poke a number of holes in it with a garden fork. The idea was to allow some exchange of water through the liner rather than rely entirely on rainfall and splash from the falls. (If I were to do it over, I would likely have eliminated the holes in the liner and had a truer “bog”, but I didn’t know if I could keep the soil moist enough with just splash from the waterfalls.)
Creating the Bog “Soil”
When you Google bog gardens, you’ll get a wide range of recipes for the soil – anywhere from 75% peat moss/25% sand to an equal mixture of peat moss, sand and local soil. The reason you don’t want a lot of the local soil is that bog plants don’t like a lot of nutrients. I decided on a mix of 50% peat moss (to keep it reasonably acidic), 25% sand and 25% soil (keep in mind that my soil is fairly sandy – if I had clay soils I might have gone with 2/3 peat moss and 1/3 sand – and I had lots of it available). I mixed all this in a wheelbarrow and filled the hole up. I then left it to settle over the winter, figuring I might have to top it up in the spring. In the spring I added another 2” or so of my peatmoss, sand and soil mixture.
Below are my video record of the construction of the bog garden, and what it looked like the first spring after it was built.
Then Came the Plants
Deciding which plants to plant was a lot easier than actually finding those plants. In addition to the Purple Pitcher Plant (Sarracenia purpurea) that a friend gave me, I also managed to locate some Showy Lady’s Slipper Orchids (Cypripedium reginae) from an orchid breeder near Toronto, and I purchased and sowed the fine, powder-like seeds of several other orchid species (unfortunately, none of these grew).
But since, like nature and a vacuum, gardeners abhor an empty garden space, I started adding some interesting non-bog plants that liked lots of moisture while I searched for the real things. These included Southern Blue Flag Iris (Iris virginica), Bog Goldenrod (Solidago uliginosa), Ohio Goldenrod (S. ohioensis), Blue Vervain (Verbina hastata), Monkey Flower (Mimulus ringens) and several others. Before I knew it, the bog garden was not only full, but full of large plants that overwhelmed the short bog plants that the garden was built for.
Now that the garden has been growing for 3 seasons and proven it works, I now have to do something about all the large plants that are taking over – including a number of volunteers that have seeded in from other gardens, including Joe Pye Weed (Eutrochium spp.), Boneset (Eupatorium perfoliatum), and a couple of asters. To that end, this fall I have started to prepare the ground for a 15’ X 15’ “wetland” that will have its own pond and be home to all these taller wetland species. Then I can get back to growing just my bog plants in the bog garden.
Building a bog garden is easy, providing you have a way to keep it moist all year long, and opens up the opportunity to grow some very interesting and unusual plants. Just don’t make my mistake of filling it up with non-bog plants – save those for a wetland or a rain garden.
From experience, I can tell you that trees and other plants readily seed into the constantly moist soil so you’ll want to make sure you remove them when they are little as they can very quickly develop expansive root systems, making them a challenge to dig out without disturbing the bog plants you want.
Below are a couple of videos I made in the first summer and in the following spring (if you’re interested in the progress). In the first video, the bog garden tours ends at about the 6 min 36 sec mark – the rest is about my pond and waterfall. The second video shows how things have very quickly started to fill in by the second year.