When building a pond, we generally have a good idea as to how we want it to look when completed. Our pond size will determine how many fish can be stocked and the pond’s shape and design will be a guide as to how it should be planted. Deepwater plants such as lilies, water Hawthorn and oxygenators such as Elodea and Hornwort are relatively straightforward to plant, difficulties however, can arise when planting marginals. These are the plants that prefer their feet to be wet, but their flowers and foliage to be proudly displayed above the water. There can be a tendency for us when planning a pond to include marginal shelf, but only one that is 9” wide (More water for the fish) and we can fall into a trap of lining our plants in a tight, regimented row along the narrow ledge that we have left ourselves. Hardly appropriate or in keeping with the overall informal shape and design of our pond. (If we buy a prefabricated fibreglass pond then we have no option but to accept the marginal shelves we’re given – not that we have to use them!)
Unsightly baskets too, if we are not careful, can soon protrude, proud of the water, again spoiling the appearance of our ‘natural’ pond.
There is another way however, of preventing our marginal plants from appearing as though they are in a military procession, head to toe on a shelf, and that is by planting them in a bog garden.
A bog garden is a dedicated area where many of the plants that are regarded as ‘marginals’ can be planted in 3 dimensions, giving natural, broad swathes of lush planting.
There are many benefits to be gained from creating a bog garden.
a. Ideal for encouraging wildlife. A bog garden presents a damp and moist haven for many different types of wildlife. Amphibia such as newts, frogs and toads adore bog gardens as they compliment their lifestyles. These moist-skinned visitors cannot afford to stray too far from their life-saving water yet enjoy a life out of water. What better place for them to ‘hang out’ than in your bog garden? A bog garden will warm up quicker than a pond giving these cold blooded tenants conditions they will not want to leave. They will also find comfort from the cover afforded by the lush green undergrowth and use your semi-aquatic garden as a safe place in which hibernate.
b. A bog garden presents you with a bonanza planting opportunities. Firstly, by electing to create a bog garden, many more plant varieties present themselves as available for your selection. Bog plants provide a range of different foliages in shape and colour not available in marginal plants and because their roots are warmer than their truly aquatic counterparts, they can provide earlier colour and growth prior to the pond plants coming to life.
A bog garden offers great planting versatility compared to a narrow planted marginal shelf in a garden pond. Through careful plant selection and construction of the bog area, it is possible to conceal the join between the pond and the garden. A bog garden should be regarded as a marshy no-man’s-land that allows the pond to blend in with the established plants in the truly terrestrial planted borders. This creeping colonisation of a bog garden is further encouraged by not having to plant specimens in mesh baskets or containers. Where these may have curtailed a plant’s aspirations to spread in a pond, plants in a bog garden are given a free-range lifestyle, colonising and spreading through your moist organic paradise in the way that nature encourages.
c. Finally, a bog garden allows you to break one of the rules of keeping koi, and that is designing a pond that incorporates plants. As koi are notoriously inquisitive fish, any plant (especially if offered in a basket of soft aquatic soil) will be investigated, sampled, and usually up-rooted. By adding a bog area around parts of the pond’s perimeter, aquatic planting is made possible while keeping them out of temptation’s way.
Methods of constructing a bog garden.
Essentially, there are two options when considering a bog garden. Each requires the use of a flexible liner to allow you complete freedom when designing and constructing your own, novel bog area.
1. A bog garden as an appendage to a garden pond, that may well be designed and constructed as an integral part of the pond.
2. A ‘stand-alone’ bog garden or marsh plant area unconnected to a pond and completely fish-free.
The construction techniques are very similar in either situation, the only real difference being that a bog garden attached to a pond requires more precision when preparing the levels of the pond. This will guard against the pond draining into the bog garden. When constructing a bog garden as an integral part of a pond, it makes sense where possible to use the same piece of liner. Raising the liner to within an inch or so of the water’s surface between them, and concealing the raised pond bed with a barrage of cobbles will give the impression that the bog and pond merge into 1 body while keeping the water in the pond at bay. Also, you’ll have to ensure that there is an impermeable barrier placed between the soil in the boggy area and the adjacent ‘dry’ garden soil. Otherwise, water will be drawn up out of your pond, giving you the impression that your pond may have a leak.
If constructing a stand-alone bog garden, it is advisable to make the bog area lower than the surrounding ground and the adjacent pond so that rain water will naturally run into the boggy area.
Pond vs Bog Garden: Same material, different method.
Similar materials are used for both a garden pond and bog garden, but the two contrasting features are created by using the material in two different ways. While every effort must be taken to protect the pond’s liner with underlay, the same is not necessarily true for the bog garden.
The excavation for the bog garden should resemble a shallow basin where the sides fall gradually towards a flattened bottom. The basin should be about 2 feet deep and lined with pond liner (unless you are fortunate enough to live on clay-rich soil). Now comes the equivalent to pond sacrilege – piercing the pond liner! Unless the membrane that keeps the soil moist in the bog area is pierced, then soon enough, the deep soil is likely to become completely water-logged and anaerobic, with the rotten eggs phenomenon leading to poor plant growth. To avoid this, several initial fork holes should be made in the bottom of the liner to which is added a layer of coarse stone chippings. These will help to keep the holes clear and aid drainage. At the hole-making stage, if in doubt as to how many to make, always make fewer than you feel as extra holes can be made later on if needed, making it possible to seal any excess holes should too many be made in the first place.
The lined hole should then be given its source of life, a generous bed of well mixed, light and organically rich soil. Avoid compacting it and gently fill the depression with water to soak the thirsty soil. The bog garden can be left a day or so to check how well it retains moisture and only then, planted with a range of complimentary bog and marsh plants.
Plants for the bog garden
The beauty about planting a bog garden is that we have complete freedom as to where to place our chosen plants. Bog plants are by their nature tolerant and adaptable and will soon colonise and spread through what is a very favourable and fertile substrate.
You can try to include a graduation in the planting scheme by placing the taller plants towards the back while lower, sprawling plants will be more effective in the foreground. Furthermore, those plants that are quite tolerant of drier areas of a bog garden can be planted to the margins where they will blend with the drier terrestrial borders.
The early flowering Globe Flower (Trollius europaeus) and Marsh marigolds (Caltha palustris) will serve to brighten up the foreground of a bog garden. The Marsh Marigold will soon cover any areas of bare soil with its rampant growth, especially when unhindered by a basket. Further splashes of colour can be added with Primulas, available in many colours and shapes, from the red-hot-poker shaped P. vialii to the more delicate P. bulleyana, both early to flower. A scattering of the more delicate lanterned Frittillaries can also add some movement in a gentle breeze.
A particular fan of the moist conditions is the Arum Lily (Zantedeschia) while the closely related Hosta (H. sieboldiana) will tend to grow quite large, providing generous cover for any amphibian inhabitants. Other plants that can serve as a backdrop include the tufting Cotton Grass and any number of Iris varieties.
If your experiences with Hostas are anything like mine, you’ll know they’re slug-magnets. But by growing them in a dedicated bog area, or adjacent to a pond, you’ll probably benefit from providing the ideal habitat for frog and toads – which are your own, home-grown biological control.
The periphery of the bog area can be planted with varieties that will blend in well with any bordering terrestrial vegetation. Possible candidates for this role include the tall and Iris-like Phormium tenax and the spreading Meadowsweet (Filipendula) which may well choose to dip its feet either side of the bog garden. A superb backdrop of ferns (Matteuccia) would complete the effect.
A bog garden can provide wildlife with a valuable haven and allow you to enjoy the benefits of a wildlife pond while keeping a well stocked garden pond. Compared to the construction of a garden pond, a bog garden is very low-tech with a leaky liner and some suitable soil the only pre-requisites. As long as the potential problem of a bog garden drying out is addressed (through careful design when adjacent to a garden pond) then a marsh area should thrive to become a lush green oasis enjoyed by all, including the garden wildlife.