HOW TO EASILY GROW A BOG GARDEN

HOW TO EASILY GROW A BOG GARDEN

A bog garden is most often envisaged as simply and extension of the pond. That, after all, is the way it is with nature. Around most lakes and natural ponds lies a boggy area where moisture-loving plants abound. But a gardener, especially the species known as the weekend gardener, should perhaps take a different view. If high on your list of priorities is that your water garden should involve little maintenance and care, then you would be well advised to install a pond only. A bog garden is of course labour intensive. Moist soil is a haven for weeds. There are a number of bog plants that can hold their own against grass and weeds blown in on the wind, Eriophorutn and Hemero-callis, for example; but even a ‘wild’ bog garden will need more tending than the pool. And besides, a bog garden of this sort will only look right in a large informal setting where there are trees and shrubs to act as a natural backdrop.

There are other considerations too. Bog plants will, obviously, only survive as long as the soil is kept sufficiently moist. If you live in an area of hot, dry summers, maintaining moisture in the soil may be a constant problem, especially if water rationing is involved. A pond and its inhabitants, animal and vegetable, can endure even if the water level drops drastically. Marginals planted in baskets will survive as long as the bottom of the baskets remain in water. (A pond which actually dries up is too shallow in the first place.) But the same weather conditions which would simply lower a well-designed pond, might will dry up the bog garden. And where space is limited I would not be inclined to forego a conventional rockery in favour of a bog garden. A rockery which contains heathers and dwarf conifers — whatever else it may contain — can provide colour and leaf in winter when the bog garden and pond have little to offer.

That is the negative way of looking at a bog garden. In its favour it can be said that a pond and bog garden combined offer a far more varied scheme of gardening, the range of plants is greatly extended; and for anyone who is prepared to involve himself in the additional maintenance, the results can be very brilliant indeed. There is also the advantage that a good number of bog plants are tolerant of shade. This is worth bearing in mind if you have a shady corner close to the pond. If you live in an area of high summer rainfall, the soil round the pond may remain quite moist or damp through most of the year, and the occasional flooding of the pond should therefore satisfy the moisture requirements of most bog plants. Otherwise there are two ways of making a bog garden.

One way is to dig out the site for the pond large enough to include a bog area as well.

Across one end of the pond is built a dividing wall. This is best done in a concrete pond, but it is not out of the question to build a wall on liners such as Butyl rubber and PVC. One needs to use mortar rather than concrete, i.e. cement and sand but no coarse, sharp aggregate. (The base will need to be broad because the wall will have little or no purchase at either end.) Placing an extra strip of liner under the wall is a sensible precaution. This dividing wall should not be waterproof, but all it needs are just a few small holes to allow water to seep through from the pond without soil passing the other way. The area for the bog garden should be filled with sand (for liner ponds), cinders, gravel, etc., to about 30 cm. From the top of the wall. Above this should be built a mixture of loam, well-rotted cow manure, leaf mould or peat, and sand. The loam should make up about half the mixture, and the others should each make up about one sixth of the total. For bog plants which will not tolerate their roots standing in water, build up the bog garden in a form of a rockery at least 30 cm. Above the water table. A great advantage of this particular form of bog garden is that it does not have to be watered separately from the pond. Just top up the pond and automatically the moisture content of the bog garden is maintained. But there are disadvantages. Firstly, the rate of evaporation from the pond will be greatly accelerated. The surface of the soil will pass water to the surrounding air and draw up more moisture from the pond at a surprising rate. And that is not to mention the needs of the bog plants themselves. For this reason, this kind of bog garden is only possible if you have a comparatively deep pond, say approaching a metre in depth, although a greater depth would be no disadvantage. Secondly, it is important that the actual surface area of the bog garden should be small in proportion to the surface area of the pond, otherwise you will almost be able to watch the water level drop before your eyes in hot weather. Make the bog garden ten or fifteen per cent of the total pool area, no more. This kind of bog garden is obviously best suited to large pools both as regards depth and surface area.

If your pool is a small one, then you would be better advised to use a different type of bog garden, and in a way it is a simpler one. Dig out a trough about 30 cm. Deep and line it with polythene or cement, and in either case the lining should not be waterproof. Better still, make the trough 45 cm. Deep, the lower 15 cm. Or so consisting of a ‘V shaped channel running the length of the trough. Holes in the concrete or perforations in the polythene should be made above the level of the ‘V. The idea is that the liner will hold water up to the level of the ‘V, but above that it can seep away to prevent the plants becoming saturated and the soil becoming sour.

This method of making a bog garden offers considerable design possibilities. Do not think simply of digging out a hole adjacent to the pond. If you have it in mind to grow a large number of Primulas, for example, then the bog garden might be designed so as to wend its way round a series of boulders or trees. A circular bog garden with a clump of plants of whatever kind in the vicinity of an informal pond is certain to look artificial. Aim to make the bog garden conform to some specific focal point in the garden or some strong line. If boulders are out of the question and you already have bulbs round your trees, then the best answer might be to make the bog garden conform to the strong curves of the pond itself. Watering this kind of bog garden can be carried out by overhead sprinkler or hose pipe, but some gardeners employ a rather ingenious method. In the ‘V channel lay down a length of plastic pipe which contains a series of holes at about 60 cm. Intervals. One end of the pipe is sealed off and buried. The other end is left open and above ground. All one has to do now is connect a hose pipe to this underground pipe and the entire bog garden can be watered at the same time. Incidentally, the holes in the underground pipe nearest the inlet should not, if possible, be larger than the holes nearest the stopped end. Otherwise the water pressure may not be evenly distributed. And if you bury the pipe in gravel with the holes facing downwards, the chances of the holes becoming clogged will be minimized.

While a bog garden is usually associated with an informal pond, there is no reason why a formal scheme should not have a formal bog garden , or preferably, to give a more balanced result, several bog gardens. Take, for example, a rectangular pond. About half a metre in from each end could be placed retaining walls to provide two narrow moist beds. Irises look particularly well in a formal design. In the case of a patio pool, bog beds can be sunk in the patio, the bed shape designed to complement the pond. They can be fed by pipe from the pond although this raises the problem of leaking joints. It would be better to join the bog beds to the pond by means of a continuous channel. If the beds are on the same level as the pond then the water level will be the same in both, and this limits one to plants which will tolerate their roots being saturated. Where the pond is a sunken one, then the beds can be placed in the higher ground surrounding the pond. They can still be fed from the pond, of course, but their water table will be lower. Alternatively, the beds can be built up with bricks or cement. The area of the beds below the water table must, of course, be quite waterproof. And to prevent moisture seeping out through the bricks above that level, it is as well to line the whole bed with a liner material.

In the case of a bog garden built like a rockery, the soil on the lowest levels will contain the most water. Begin with plantings of Marsh Marigold, of Bog Arum and Forget-Me-Nots and marginals we have already considered. In addition, plantings of Mimulus or Monkey Flowers will provide masses of colour at the pool’s edge from summer until the first frosts of autumn. And they will flower even when, through lack of room or soil, they do not attain their full height. Mimulus is a primary choice for the small pond. The plant sets seed easily, especially if raised in a cold frame, so that quantities of their showy flowers, rather like open-throated snapdragons, can be had in a few seasons. And if that is not praise enough, one can add that Mimulus comes in a variety of colours and shapes. Most of the species come from North America, including Mimulus luleus which has naturalized itself in Europe. The flowers are yellow. M. guttalus is similar except it has reddish blotches or spots on the flowers. Crosses between the two are common. They grow to about 45 cm. But are often a great deal shorter than that. The Monkey Musk, M. moschatus, grown for generations for its distinctive perfume, is a creeping plant of low habit. The flowers are pale yellow and not very conspicuous. The plant is mainly suited to very small ponds and has, incidentally, lost its scent. The ‘hose-in-hose’ varieties are well worth growing, but are not quite as spectacular as M. cardinalis whose flowers are a vivid combination of scarlet and yellow. If you want a Mimulus that will grow with a few centimetres of water over its crown, then choose M. ringens, a species which grows anything from 20 to 90 cm. High and produces flowers of violet or blue. To these, in moist soil, one might add White Bachelor’s Buttons green, finely divided leaves will combine beautifully with other plants. And there is a yellow version, R. acris flore pleno, 60 cm. High, which produces lovely double buttercup flowers in profusion throughout the summer.

But for many people the desire to grow bog Primula will be the main reason for building a bog garden. Primula favour moist, rich but not sodden soil and they certainly dislike sourness. In shade or full sunshine, they can provide a pond with a lightness and gaiety that I do not think is rivalled by any other moisture-loving plant; and they have an exceptionally long flowering period. They are most effective when grown in large clumps, one colour giving way to another. Propagation may be carried out either by seed or division. Immediately the seedlings have ripened, place them in shallow trays containing two parts of loam, two of leafmould and one of sand. Barely cover them with compost and place the trays in a cold-frame, shielded from strong sunlight if necessary. Germination takes place in about four weeks. The seedlings should be pricked out as soon as they are large enough to be separated easily and placed in outdoor boxes, and from there into the bog garden. Many primulas will seed themselves naturally too, and where cross-fertilization takes place you will find new blends of colour and sometimes spotted or blotched forms.

To begin the season early, plant the small Himalayan Primula denticulata which will pro-duce globular clusters of lilac, red or white flowers from March onwards. It is satisfied with a modicum of moisture, so it can be placed in the drier parts of the bog garden. For wet soil, the obvious choice is from the candelabra varieties. P. japonica, 45 cm. High, produces up to six tiers of the most vivid red to purple flowers in many shades and there is a white form too. P. beesiana, a Chinese bog primula, has the distinction of purplish-red flowers with yellow centres. Both these plants seed themselves very readily. So too does the large P. pulverulenta, 90 cm. Tall with its many tiers of purple flowers. And there are many hybrids available, including the famous ‘Bart-ley strain’ of apricot, buff and many hues of pink. With the larger pond still in mind, one might add the giant Himalayan Cowslip, P. florindae, which also reaches about 90 cm. In height; or what is regarded as a more elegant if less showy form, P. sikkimensis, 60 cm. High. The miniaturist might choose the red to lilac P. frondosa or the carmine P. rosea. Neither of these grows much above 15 cm. But whatever varieties or cultivars you select from this large field — and is there such a thing as an ugly primula? — grow them in scores, all of them. Occasionally one sees primulas displayed in something approaching neat rows in botanic gardens. That is a useful scheme where identification is the first requirement. But the effect is rather stark. In a bog garden, primulas are shown to best effect when combined with other plants. Where space permits, the primula makes an excellent partner with hardy ferns, whose cool, peaceful ambience will heighten the primula’s brilliance.

For the water’s edge, probably the finest fern you can grow is the Royal Fern, Osmunda regalis. It does have a regal height, however, and can reach a metre and a half in rich, peaty and moist soil. Better suited to the medium sized pool is Matteuccia struthiopteris, or Ostrich Feather Fern, which rarely grows more than 90 cm. High. Its fronds grow upwards in a circular form, looking as much like a giant shuttlecock as the plumage of an ostrich. Its roots are stoloniferous, as are those of Onoclea sensibilis, a more vigorous plant though smaller, at 60 cm. On average (in America it is found rather too rampant). It is a fern which will do well in comparatively dry situations as well as in wet, provided it is not exposed to too much sunlight. For finely cut fronds of vivid green, one can hardly do better than choose the well-named Lady Fern, Athyrium filix-femina. It grows about a metre high in moist, shaded or partially shaded positions. Rather smaller is the Hardy Maidenhair Fern, Adiantum pedatum, generally thought of as one of the most beautiful of ferns. It grows 60 cm. High, requires shade and shelter, and like most ferns appreciates soil rich in humus. This is a useful plant for floral decoration.

For the rockery, an easy fern to grow is Dryopteris dilaiaia known under the lengthy title of Broad Prickly-toothed Buckler Fern. It is a fern which suits the larger bog garden since it can reach a metre and a half in height. For compactness and a very satisfying shade of rich green, I would include plantings of the only grows about 70 cm. High; moreover there are a number of fine cultivars from which to choose. Of much the same height is the evergreen fern Blechnum spicant, whose fronds are divided into narrow pinnae or leaflets which gives the plant a rather wiry appearance. It is a distinctive feature although not one to create the sort of soothing ambience one associates with ferns. To provide a carpet effect, always useful when combining other low-growing bog plants, you might use Blechnum penna-marina. The fronds are of a very dark green and only about 15 cm. Long. It has an informal habit, some of the fronds growing upright or partially so, others quite prostrate. The plant is evergreen. And so is the strap-like Hart’s Tongue, Phyllitis scolopendrium, a fern very common in parts of the British Isles and Ireland. There are many variations of the common form, cristatum for example in which the ends of each frond are conspicuously divided; and if you have a rustic bridge, a rocky waterfall, little nooks or crannies in the rockery, then this is the fern with which to fill them. Another is Poh/podium diversifolium, a native of Australia and New Zealand, with long, finger-like fronds. Many ponds are built in the vicinity of dry stone walls. If you want a dainty fern for such a position, then Asplen-iurn trichomanes, the Maidenhair Spleenwort, will meet your need.

Ferns loomed large in folk lore. Once it was believed that the little folk went trysting, borne aloft on aerial steeds made of fronds. Another belief was that whoever could capture the seed of a fern, which made its appear-ance only at midnight on midsummer’s day, would receive magical powers. Ferns also played a part in love potions (they can be poisonous, in fact). The old beliefs are gone, but to walk through a glade of ferns is to know that their mystical atmosphere remains.

Hosta is another plant that combines well with Primula. It likes a rich, deep, moist or damp soil but is not particular as to sun or shade. The plant is grown primarily for its broad and compact leaves, the flowers in many cases being uninteresting and sometimes partly hidden between the leaves. An exception is to be had in H. ventricosa, whose large purple to blue flowers rise well above the leaves. But its overall height of 90 cm. Makes it rather too large and bulky for many gardens. H. lancifolia, 60 cm. High, with dark green though not particularly broad leaves, is more suited to the smaller bog garden. Preference might be given, though, to H. glauca, which has glaucous leaves of rich blue, whose leaves are less blue but whose pale lilac blooms appear on top of tall stalks. For dramatic effect, you might choose H. fortunei marginata alba, whose dark green leaves are edged with white or cream. This is a most conspicuous plant. Do remember, however, that if you are growing the variegated forms of such plants on, the effect of green and cream and white, endlessly repeated, can be rather overpowering. One can have too much of a good thing. The new pond owner almost always overlooks grass-like plants in favour of more colourful ones. This is a pity. They provide the water garden with a dignity few other plants can equal. This is especially true on calm, still days when the reflection of muted colours in the pond will evoke a sense of placidity which irises, for example, by their very colourfulness cannot do. Moreover, plants whose beauty lies in their leaf and shape are of two metres and more — are the largest that can be grown in temperate zones. The plant itself can reach a height of 4.5 metres. A native of Brazil, Gunnera is named after J. Ernst Gunner, a versatile individual who combined the roles of bishop and botanist. Doubtless it is the very massiveness of the plant which has made it so popular, although it is not fully hardy. To protect from frost it needs to have its leaves doubled over the crown in the autumn and this will provide it not only with protection but with a mulch. No other treatment is necessary. However, to my mind, unless planted in a spacious garden and unless its site is congenial and the plant attains its attractive throughout the whole growing season. If you are not including Sweet Galin-gale (Cyperus longusl in your scheme, then Carex stricla or pendula will create the same elegant effect. So too will the lovely C. riparia ‘Bowies’ Golden’ which needs very wet soil or shallow water and grows no more than 40 cm. High. More than most plants, these sedges will give the impression that your pond has existed for years: they mature the scene. And for the larger scheme, Pampas Grass, Cortaderia argentea, has a warming as well as a maturing effect. The plumes are white or silvery and sometimes touched with lavender, while the plumes of the less well known Cortaderia quila have a definite lavender hue and are, if anything, even more feathery. They are excellent subjects for reflection close to the pond. Coming from South America they appreciate a certain amount of shelter. Perhaps no other plant is more often grown where it is ill-suited than the mighty Gunnera manicata.

Beside a small or even medium-sized pond, Gunnera appears not so much a dominant, imposing plant as a clumsy intruder. It is only in the context of a vast expanse of water that the true magnificence of this plant becomes apparent.

And much the same can be said about the rhubarbs, such as Rheum palmatum, whose deeply lobed leaves create a fine impression of opulence on a plant that can reach 2.5 metres and more, and which produces panicles of creamy white flowers. Rheum palmatum alrosan-guineum has leaves even more deeply dissected and magnificent flowers of brilliant crimson. But the owner of the small garden would be best advised to resist such glories and include a dwarf species such as Rheum inopinatum, 60 cm. high. Not that the compromise is a great one; this little plant has conspicuous red veins and stems with greyish-green leaves and scarlet flowers. Rheum, conveniently, likes to be left undisturbed for years and does best in rich, moist soil and some shade. More shade and less moisture suits Rodgersia, a genus much admired for both its foliage and flowers. Rodgersia pinnata alba has dark brownish-green leaves and white flowers, while R. pinnata elegans has a more bronze tint in the foliage and red flowers. As neither of these plants is likely to exceed 60 cm., they can be accommodated in most schemes.

And no bog garden of whatever size should be without a few varieties of Astilbe. Few moisture-loving plants are more obliging as regards situation and none is more spectacular. Any soil will satisfy these plants and while they respond to plenty of moisture in summer, very satisfactory results can be obtained in less than optimum conditions. Their flowers are borne in soft, feathery and pointed plumes. The flowers of the large Aruncus Sylvester (Spirea aruncus) and the smaller fine-leaved A. kneiffi are not dissimilar to those of Astilbe. And the flowers of Rodgersia and of Spirea, although lacking the same pointed tops, are often confused with Astilbe. All these plants are well worth growing for their soft, fluffy plumes, as is the Double Meadow-sweet, once classified as a Spirea but now called Filipendula ulmaria plena. But what can equal the radiance of Astilbe blooms caught in the bright sunshine of a summer’s day or their soft, glowing colours contained in a shady glade? Astilbes bloom from June to August and varieties abound. There is a fine choice of colours in the Arendsii cultivars: pink, red, white and mauve, ranging in height from 60 cm. To 1.8 metres; and there is a little Japanese form, A. simplicifolia, which is only 22 cm. High. It produces a little frothy spire of pink flowers. Propagate Astilbes by division.

No less easy to grow is Hemerocallis, derived from the Greek ‘for a day’, hence the common name of Day Lily. Despite the short life of the individual bloom, the Day Lily flowers over a long period, and if a number of different hybrids are planted, one can expect blooms to appear all summer long. They need little or no tending, improve with the years, and they are forceful enough to defeat a multitude of weeds. Hemerocallis comes in innumerable hybrids mainly of orange and yellow, but also of pure white. Like Astilbe, Hemerocallis thrives in moist soil, but I feel these plants should not be placed together, although this is often recommended. The light green foliage of the Day Lily is justly admired, but it is altogether coarser than the finely divided leaves of Astilbe. Moreover, the flowers of the Day Lily are strong and definite rather than light and fluffy. To combine these two plants is, to my mind, rather like laying a table with both pottery and cut-glass. Certainly there is room for Hemerocallis and Astilbe in the same bog garden, but divide them by rocks or ferns. And if you want a companion for the Day Lily, choose from among the cultivars of the Globe Flower or Trollius europaeus, whose yellow, white and orange blooms will mix well, while their globular shape will add an element of contrast.

And whatever selection you finally make among the many bog plants available, apply the same rule to them as to marginals. A series of large plantings of several plants is better by far than smaller groups of many. Resist the temptation to buy too wide a variety of plants. Having stocked the pond with water-lilies, marginals and bog plants, one can now turn one’s attention to another dimension altogether: that of fish and animal

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