Oligotrophic bogs and fens

All the species mentioned in Table 8.3 are dependent on low-nutrient levels. In artificial ponds, sealed with a chemically inert material, such as plastic sheets or synthetic resin, this situation can often be found when nutrient poor substrates and rainwater or mains water is used (Figure 8.14). Only if such conditions are guaranteed is such a planting sustainable in the long term. Normally such plantings will only be established in small areas. Depending on the hardness, or rather the acidity of water, we can distinguish between lime-fen, acidraised bog and transition-bog plantings.

Vegetation of raised bogs grows best under conditions with low water hardness and pure Sphagnum peat substrate, or around 5 cm of peat stacked on lime-free sand. On this wet acid-substrate, Sphagnum mosses can be established as ground-cover vegetation. Pure raised bog-species are able to grow within this living Sphagnum layer, as they are able to grow continuously through the permanently expanding mosses. Conditions between both the aforementioned possibilities can occur, for example, on a poor acid substrate and semi-hard water. Here it is possible to establish most of the plants recommended in Table 8.3. Even here scattered clumps of Sphagnum species can be established. The acidification caused enables adequate growth conditions for raised-bog plants placed just into the moss-clumps.

Although in several European countries, Sphagnum peat is viewed as a renewable resource and is acceptable as a horticultural product, in other countries (notably the UK), the use of peat is

8.17

Oligotrophic lime-fern with Cotton Grass in Southern Germany

8.18

Wooden half-barrel used to store rainwater in a winter garden. This oligotrophic environment is suitable for establishing bog vegetation, carnivorous Darlingtonia californica, and Drosera species grow well

actively discouraged. This is because semi-natural raised bogs are a rare and declining habitat, and are threatened by peat extraction. In these instances, lime-free sand can be used as a lower layer and be covered with a thin peat layer (2-3 cm are enough) or living Sphagnum plants. In a correctly worked out planting, the Sphagnum plants will not die but will develop into a dense blanket. Coir or composted pine-bark can be used as a substitute, as can timberfibre substrate (‘Toresa’).

Artificial-bog vegetation can produce an exciting effect with intricate combinations of cotton grasses, insectivorous plants, dwarf shrubs, orchids, semiparasites, and several ornate species between dwarf grasses and mosses. The ground-covers are indispensable for both an optimal visual effect and the best growth of bog forbs. These are mostly rooted very weakly and need the strength of the surrounding vegetation to secure them in place (Figure 8.15).

For example, the author has observed the best germination of orchids between grasses and Irises. Semi-parasites of the genera Rhinanthus, Pedicularis and Castilleja should be sown near grasses in autumn, so that they can find and penetrate the roots of these potential hosts after germination in early spring. Their long-lasting flowering period results in a little weaker growth of the grasses. The poorly competitive Mimulus primuloides, Pinguicula grandiflora and Primula frondosa should be placed on bare soil. They will be overgrown by invading ground covers but can move to new gaps by self – seeding.

Table 8.3. Oligotrophic bogs and fens Origin* Soil/water conditions Height (cm) Flowering Months Flower Colour Dominant species (5-20/10 m2) Andromeda polifolia Eur, N-Am, As Raised—transition bog 15-25 IV-V white Carex diandra Cosmopolitan Transition bog— lime-fen 20-60 V-VI brown Cypripedium reginae N-Am Transition bog— lime-fen 50-80 V-VI white, pink Darlingtonia californica+ N-Am Raised bog 30-40 VI-VII red Eriophorum latifolium Cosmopolitan Transition bog— lime-fen 40-80 IV-V white Eriophorum vaginatum Cosmopolitan Raised bog 30-50 IV white Gentiana asclepiadea Eur, W-As Transition bog— lime-fen 30-40 VII-IX blue Iris sibirica E-Eur, W-As Transition bog— lime-fen 70-80 V-VI blue Kalmia polifolia N-Am Raised bog 30-50 V red Ledum groenlandicum N-Am Raised—transition bog 50-100 V-VI white Lythrum salicaria ‘Robert’ cultivar Transition bog— lime-fen 30-50 VII-VIII pink Molinia caerulea Eur, N-As Transition bog— lime-fen 40-80 VIII-IX brown Sarracenia flava+ N-Am Raised bog 40-60 VI-VII yellow Schoenus nigricans Eur, Am, W-As Lime-fen 30-50 V-XI black Trollius europaeus Eur, As, N-Am Transition bog— lime-fen 40-50 V-VI yellow Zigadenus elegans N-Am Transition bog— lime-fen 50-90 VI-VIII white Companion species (20-60/1 0m2) Arnica montana Eur, As Raised-transition bog 30-40 V-VI white-pink Carex capillaris Cosmopolitan Lime-fen 15-25 V-VII Carex echinata Cosmopolitan Transition bog 20-40 V-VII green

Carex flava ssp. flava	Eur, N-Am	Transition bog— lime-fen	30-40	VI-VIII	green
Epipactis palustris	Eur, W-As	Transition bog— lime-fen	40-50	VI-VIII	red-white
Erica tetralix	N-W-Eur	Raised-transition bog	20-30	VI-VIII	pink
Eriophorum russelianum	N-As, N-Am	Raised-transition bog	20-40	VI-VII	orange
Gentiana pneumonanthe	Eur, W-As	Transition bog	20-40	VII-IX	blue
Helonias bullata	N-Am	Raised-transition bog	20-40	V-VI	pink
Iris setosa ssp. canadensis	N-Am	Transition bog	20-30	V-VI	blue
Narthecium ossifragum	Eur	Raised bog	10-30	VII-VIII	yellow
Sarracenia purpurea	N-Am	Raised bog	15-30	VI-VII	red
Tofieldia calyculata	Eur	Transition bog— lime-fen	15-30	VI-VII	yellow
Trichophorum caespitosum	Cosmopolitan	Raised bog	5-20	V-VI	white
Vaccinium macrocarpon	N-Am	Raised bog	3-5	VI-VIII	red
Vaccinium oxycoccus Ground-cover plants	Eur, N-Am (up to 120/10 m	Raised bog 2)	3-5	VI-VIII	pink
Carex davalliana	Eur	Transition bog— lime-fen	10-40	V-VII	brown
Carex viridula	Eur, N-Am, As	Transition bog— lime-fen	10-15	VI-VIII	green
Mimulus primuloides	N-Am	Transition bog— lime-fen	3-5	VII-IX	yellow
Schoenus ferrugineus us	Eur Eur	Lime-fen Lime-fen	15-30	V-XI	brown
Trichophorum alpinum num	Cosmopolitan Cosmopolitan	Transition bog Transition bog	10-20	V-VII	white
Sphagnum-mosses—cuttings pressed on wet soil surface of acid, oligotrophic sites: S. palustre, S. squarrosum, S. angustifolium, S. magellanicum

Scattered plants (up to 50/10 m2)

Allium angulosum	Eur, W-As Eur, W-As	Transition bog— lime-fen Transition bog—lime-fen	30-60 30-60	VII-VIII	red
Allium suaveolens	Eur	Transition bog— lime-fen	20-40	VIII-IX	pink
Aster nemoralis	N-Am	Raised—transition bog	15-25	IX-X	pink-violet
Dactylorhiza spec. & Hybrids	Eur	Transition bog— lime-fen	20-40	V-VI	pink
Dianthus superbus	Eur, N-, E-As	Transition bog— lime-fen	30-40	VII-IX	pink
Drosera anglica	Cosmopolitan	Raised—transition bog	5-20	VII	white
Fritillaria meleagris	Eur, As	Transition bog— lime-fen	25-30	IV-V	white/violet
Gladiolus palustris	E-Eur, C-Eur	Transition bog— lime-fen	40-50	VI-VII	pink-red
Pinguicula grandiflora	Eur	Transition bog— lime-fen	5-15	V-VI	blue
Parnassia palustris	Eur	Transition bog— lime-fen	10-20	VII-IX	white
Pogonia ophioglossoides	N-Am	Raised—transition bog	10-15	V-VI	pink
Rhynchospora alba	Eur, N-As	Raised—transition bog	25-30	VI-VIII	white
Primula frondosa	E-Eur	Transition bog	5-10	IV-V	pink
Spiranthes cermia	N-Am	Transition bog	30-40	IX-X	white
Swertia perennis	Eur	Transition bog— lime-fen	15-50	VI-VII	violet
Viola palustris	Eur	Transition bog	5-12	V-VI	blue
Sown species (hemiparasites)
Castilleja miniata	N-Am	Transition bog	20-50	V-VIII	orange
Pedicularis palustris	Eur, As	Transition bog— lime-fen	20-50	V-VI	red-pink
Pedicularis	Eur, As	Transition bog—	50-100	VI-VII	yellow

sceptrum – lime-fen carolinum

Rhinanthus Eur Transition bog— 30-50 VI—VIII yellow

serotinus lime-fen

* Eur=Europe; As=Asia; Am=America; N=North; E=East; S=South; W=West; C=Central + Slight frost protection recommended in cold regions

8.19

Wastewater treatment system with plantings of Carex acutiformis and Scirpus lacustris in Friedrichsrode, Germany. In the middle there is a pebble bed planted with bactericide Mentha aquatica