The bog garden
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To the inexperienced the idea of a bog garden can seem to be almost a contradiction in terms because good drainage is important for most plants if they are to flourish. However, gardens often have areas that are difficult to drain because of nearby creeks or stormwater drains, or where the work involved in drainage is just not practical. Frequently, such wet patches are eyesores, but they give you the opportunity to create something wonderful — a bog garden, which may well become the most beautiful part of your garden.
Because the bog garden is a natural transition area between wet and dry, it’s usually easiest to construct, and works best, if it can be incorporated as part of a larger garden — ideally between a woodland area and a stream or pond. If you read the recent Growing Today articles about water gardening you will have a good idea of the plants that do well around the margins of a stream or pond, the flag irises and rushes, for example, but what of that area of constantly wet soil around the waters’ edge that gradually and imperceptibly merges with the rest of the garden?
That’s the home of the bog garden plants, they act as the link between a water garden and the drier areas. Most of them will grow well under normal garden conditions, but if they have to, they will tolerate very wet soil. The best bog plants, such as the candelabra primroses and astilbes, are equally at home in the perennial border or at the waters’ edge.
There is a large range of bog garden plants, most are perennials, but they span all sizes from minute ground covers to some of the largest perennials. The area you have to work with will largely dictate your choice of plants. Those working on a large scale will have room for the giant rhubarb-like leaves of Gunnera, and the other large bog plants, such as the various Rodgersia, Aruncus and Filipendula species. However, many gardens cannot cope with such large plants, in which case the likes of bog primroses, Darmera peltata and the many Astilbe species and cultivars will be better suited.
The type of wet area you are working with will also influence your plant selection. Choosing the second tier growth to go behind the marginal aquatic plants is fairly straightforward if you are working with a pond because the chances are that the water level will remain fairly constant throughout the year. Areas of wet soil are also quite easy to work >with , but there may be times when they dry out entirely or there may be occasional floods. Such extreme variations of moisture level can be difficult to cope with. Working around a stream can be tricky as the water level tends to rise and fall with rainfall and the seasons. The plants right at the waters’ edge have to be able to cope with varying water levels, or you have to find some way around the problem. It’s usually best to construct a stone or timber retaining wall up to the presumed high-water level and build the garden above that level. Alternatively you will have to edge the stream with plants that can tolerate large changes in water level. The sedges, Japanese and Siberian irises come to mind as good choices. For smaller areas try Mimulus, Scrophularia, the marsh marigolds (Caltha and Ranunculus) and the skunk cabbages (Lysichiton americanus and L. camschatcensis), if you can get them.
Arranging the plants demands attention to the details of growth habit, flowering season, colour and foliage type. It’s usually best to grade your plants on the basis of size, but if you are using the larger species you will also have to consider shading and growing season. For example, it’s possible to grow bog primroses with Gunnera because the primroses will usually flower and begin to die back before the large leaves of the Gunnera shade them out. Astilbes, however, will still be actively growing when the Gunnera leaves have reached full size and they will become leggy and drawn through excessive shading. Most bog plants tend towards white, pink, mauve and purple flowers that blend well together, but oranges and yellows are not uncommon, so take care to avoid any really shocking colour contrasts.
As you move away from the area of constantly wet soil the plants become more typically woodland. We move through the water forget-me-nots and Lysimachia to the hostas, Meconopsis species, ferns, foxgloves, Dicentra, Campanula, Thalictrum and Pulmonaria. These are all good choices as they can tolerate periods of wet soil, while really being more at home in a woodland setting. Solomon’s seal (Polygonatum × hybridum) is a very good plant for the transition between bog and woodland. It grows large enough that it can compete successfully with the stronger growing bog plants. Sure, it can be a bit invasive, but it needs to be if has to grow with Rodgersia and Gunnera.
By now you will have noticed that most bog plants are spring flowering. It’s true that by early summer most of the flower display is over, but bog plants display a wealth of different foliage types and that’s where their true beauty often lies. Aim for a varied blend of foliage rather than a wealth of flowers. The subtle variations of colour and texture between the foliage of hostas, perennial lobelias, astilbes and the calla lilies creates at least as much interest as their flowers and is certainly longer lasting.
You will also have noticed that most of the plants mentioned prefer shade. A bog garden is at its best in the light shade cast by deciduous trees and that’s why it blends so well with a woodland garden. Perfecting the gentle transition from trilliums and wood anemones to hostas and ferns and on to the real moisture lovers like bog primroses, then finally to the irises and the true aquatic plants enables you to create a microcosm of the natural environment. A bog garden typifies all that is best in gardening with perennials: there’s the colour of spring flowers, the lushness and variety of foliage, and the interest of variable growth forms.
The ideal bog garden demands to be part of a larger garden scene, but even with limited space there’s room to take advantage of the beauty of these plants. Simply excavating a large hole and lining it with polythene will enable you to create a patch of constantly moist soil. You won’t be able to work miracles with such a basic setup, but you will be able to widen the scope of your gardening, and that’s what it’s all about — adding interest through adding variety.
Copyright Geoff Bryant
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