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

Oligotrophic bogs and fens

8.17

Oligotrophic lime-fern with Cotton Grass in Southern Germany

Oligotrophic bogs and fens

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

Oligotrophic bogs and fens

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