Bog garden Design and Plants
No water garden is complete without a bog garden as some of the most beautiful and interesting plants thrive in such situations. Many ponds and lakes have a natural perennially damp surround which requires no more attention before introducing plants than to remove unwanted weeds.
If the pond is fed by a natural water supply, it is usually possible to channel the overflow into surrounding land, thus producing an area which is permanently moist without being waterlogged. Alternatively, any low-lying site with a clay subsoil can be periodically flooded over with water to produce a bog garden. During the winter months, rain will supply all the moisture that is required as most bog plants are then dormant.
To make a bog garden on raised ground or where the drainage is very free, creates a different problem which, however, can be overcome with a little effort. Excavate the site to a depth of 38cm (15in) and line the area with poor quality concrete consisting of 12 parts of ballast to 1 part of cement or even weaker, or cover the base with slates, tiles or asbestos sheets slightly overlapping. Another idea is to line the base with a single layer of 500 gauge polythene sheeting perforated in a few places so that it allows water to leak away slowly.
Whatever method is employed, put 6-8cm (23in) of stones or pebbles over the lining to provide adequate drainage. Cover these with a layer of peat tailings or old turves turned upside down. Replace the soil, incorporating liberal quantities of peat, manure or other fibrous material to hold the moisture during times of drought. When finished, the top soil will look like any other herbaceous border, but the roots of the plants will feel the influence of the water, and such conditions should produce an ideal bog garden. Although it is important to water the area in dry weather, it is equally important never to allow the soil to become waterlogged.
Suitable plants There is a wide range of plants suitable for the bog garden. Some of the more popular and interesting kinds include the aconitums (monkshood). The most commonly grown species is A. napellus, with finely cut leaves and purplish-blue flowers, its variety bicolor, with blue and white flowers, and ‘Newry Blue’, flowering June-July on 1-1.3m (3-4ft) stems.
Aruncus sylvester (goat’s beard) if space permits, is a wonderful plant for the back of the bog garden, with large plumes of creamy-white flowers in June and foliage very similar to that of the astilbes and growing to 1.3-1.6m (4-5ft). The numerous varieties of astilbe make excellent bog garden plants, but unfortunately they are frequently grown in dry borders with inadequate moisture, where they never acquire their full splendor. Some of the most popular varieties include: ‘Deutschland’, pure white, ‘Fanal’, deep red with reddish foliage, ‘Koblenz’, rose, ‘Red Sentinel’, very deep red and ‘Rhineland’, bright pink.
The native marsh marigold (Caltha palustris) in both its single and double-flowered forms, is a fine plant for really moist soils. It makes a bold splash of yellow in spring.
Gunnera manicata is probably the most impressive bog plant it is possible to grow in this country, but it is only suitable where there is ample room, as in a large water garden. The foliage resembles enormous rhubarb leaves, often reaching 2.5-3.3m (8-l0ft) in diameter, on stems 3.8m (12ft) or more in height. The flowers are brown—borne in heads about m (3ft) long and something like a bottle brush in appearance. Gunneras require plenty of moisture during the growing season but must not become waterlogged, especially during the winter months, when it is necessary to give the crowns protection by packing the dead leaves over the roots. Extra protection with straw or leaves should always be added in very severe weather.
No garden is complete without hemerocallis (day lily). The species come from Asian riversides and will grow anywhere in the bog garden, in shallow water, in shade or full sun, in heavy wet soil or dry sandy situations. Many hybrids have been produced, giving a wide variety of color from pale yellow to deep red and a flowering period from June to September. Given ample room for development, the plants may be left undisturbed for years. A vast range of hybrids include: ‘C. P. Raffill,’ 0.7m (lift) apricot flowers, July-August; `High Tor,’ 2m (6ft) or more in height, yellow flowers, June-July; ‘Pink Damask,’ rich pink, and ‘Hiawatha,’ 0.7m (2 1/2ft), copper-red.
Hostas are invaluable semi-shade plants with leaves in various shades of green or green and silver or gold variegations and pale mauve or white flowers. Species include H. fortunei alba, yellow leaves edged with green; H. sieboldiana, blue-green foliage; H. undulata, large oval leaves; H. minor, 30-38cm (12-15 in), pale green leaves and white flowers.
Iris kaempferi and its forms are the most notable of the bog iris. Natives of Japan they are grown beside the paddy fields which are flooded during the summer months but drained in the winter, thus producing ideal growing conditions. As they are lime haters, they must have adequate peat or leaf mold in the soil. These plants are rarely sold as named varieties, but usually as the ‘Higo Strain’ of hybrids.
Lysichitum americanum, the skunk cabbage, indigenous to North America, has large bright yellow arum flowers in April, before the leaves, which make a bold show at the pool side during the summer months. L. camtschatcense from Japan has white flowers and is less vigorous than its American counterpart.
Bog primulas provide some of our best waterside perennials, especially when grown in semi-shade with a background of moisture-loving ferns. Among the best are P. florindae, 0.7m (2.5 ft) sulphur-yellow flowers, June-July; P. japonica splendens, crimson-purple, May-June; P. japonica ‘Postford White’, an outstanding candelabra type with white flowers; P. pulverulenta ‘Bartley Strain’, rose-pink flowers, May-June and P. viali, with mauve flowers, which has bright red buds before opening.
Moisture-loving ferns make an excellent background for bog and water gardens with some shade. Matteuccia struthiopteris, the ostrich feather fern has symmetrical 1m (3ft) long fronds like a shuttlecock. Onoclea sensibilis (the sensitive fern) thrives in shade and moisture and has pale green fronds, 0.3-0.4m (1-1.5 ft) long; Osmunda regalis the royal fern is a noble plant, easily grown if given an adequate water supply. When well established it reaches 1.6-2m (5-6ft) in height and will set off any bog or water garden.