The Peat Garden Edinburgh Botanics circ 1976
The Peat Garden and it's Plants
by Howard Drury
Introduction
Peat gardens have sporadically occurred during the past 80 years. Earliest references refer to the peat walls at Logan Botanic Gardens, Stranraer, in R.H.S. Journal, 1927. Peat walls were used to retain soil for seedlings of Forest's Rhododendrons from China. Amongst the seedlings appeared Primula and Meconopsis, possibly by accident. Many plants produced seed, which readily germinated in the ideal conditions. With increasing environmental pressures on peat bogs, we now need to find alternative materials to ensure many of the rare plants previously grown in peat walls are not lost forever.
Staff from Edinburgh visited the garden and decided that a similar feature would be valuable to Royal Botanic Garden Edinburgh, in spite of the change in climate, i.e., Stranraer being in the warm westerlies of Mull of Galloway. Edinburgh's experiment become very successful and contains plants from the Himalayan Regions, Europe, South Africa, Japan, and the Americas. As a result of Edinburgh's example, many famous gardens had included peat gardens in their plans. These include gardens such as R.H.S. Garden at Wisley, Kew Gardens, Harlow Carr at Harrogate, Liverpool Botanical Gardens at Ness and the Savill Gardens at Windsor.
The staff at Logan Garden are now constructing a new peat garden based on the original Edinburgh design. At the same time, the original peat walls at Edinburgh became infected with several serious weeds and are currently being rebuilt.
In some cases peat blocks may replace part of the rock garden particularly a low-lying area, or in other cases a separate area is dedicated to peat gardening. Even a stone trough carefully sited and planted can suffice.
Why peat gardens? Why not a traditional rock garden? The answer is simply that peat gardens offer a whole new concept in gardening, a new environment in which to grow small, and until recently, plants considered difficult. Unlike a “rock” garden, peat gardens are built in such a manner and of such materials that roots run through the peat blocks, knitting them together. Indeed, it is truly amazing how quickly a row of brick like blocks is transformed into a cover of shrubby plants.
A peat garden can be sited in a very small space, often on the North side of buildings. Although never successful directly under tree canopies, they may be sited on the shady side of trees and shrubs. A lower moist slope or even the base of a North wall will suffice. Indeed, a peat garden is ideally situated in a small modern town garden, which is enclosed by interwoven fencing. Peat gardening is in its infancy, and every year more gardeners are taking up the challenge it offers.
Weeds
With such a wide range of plants as found on peat walls, it is impossible to use selective weedkillers once planted. Chemical weed control is also typically untidy in its results. A weed is frequently described as a plant growing where it should not be, and in peat gardening these 'weeds' are often difficult to remove. Creeping stoloniferous perennial weeds are a nightmare, their underground shoots becoming embedded in the peat blocks.
The late Alfred Evans of Edinburgh Botanic Garden
Many of the plants used in peat gardening resent disturbance at all, and some are very surface rooting. In view of these facts, it is best to remove all weeds at as early a stage as possible by hand. Larger perennial weeds may be eased out with a hand fork, but the use of a hoe or border fork should be completely ruled out.
Some weeds such as Cardamine hirsuta (Bittercress) produce vast quantities of seed only a few weeks after germinating themselves, and therefore they should be removed as soon as possible. Other weeds may in fact be plants which have become uncontrollable. Primulas, for instance, produce vast quantities of viable seed which often germinates after a mild winter.
Some plants such as Uvularia sessilifolia sends rhizomes out throughout the peat bed, coming up through the choicest of plants. The answer here is to be very selective when choosing plants and don't jump at gifts from friends ‑ they have probably got lots of it to give away.
Environment
The challenge of a peat garden can provide the gardener with a new microclimate that can accommodate a very wide range of new, highly decorative plants which would be otherwise impossible to grow. Wet peat moistens and cools the atmosphere in the vicinity, and many woodland plants revel in this freshness. The soil should be slightly acid or at worst neutral.
Few peat gardens have been established in alkaline soil, but even using a technique of isolating the acid peat bed from the alkaline soil by raising it up has its shortcomings. Being raised and draining quickly one has to turn to the local water supply, which is also usually alkaline, to irrigate the peat bed and this often results in the death of many plants. Assuming one has an acid or neutral soil and wants to start a peat garden, then the challenge can be very daunting.
It must be said at this stage that the level of maintenance is high and the number of mistakes can also be high, but by learning from your own and others mistakes and problems, then the rewards can be considerable. The growing and knowledge of peat plants will be much valued by many.
As already stated, the object in building a peat garden is to provide a cool summer environment, possibly partially shaded, with a moisture retentive soil. This soil must not, however, be waterlogged, and it may be necessary to install drains to run the water away into either a drain or a soak-away. A gently sloping site is ideal, but the lower part of a slope could be a frost pocket, and this can have devastating effects on choice but otherwise hardy plants which are just coming into growth.
A little shade is a good thing, but heavy shade from overhead canopies should be avoided. While the shelter provided could be beneficial, the drips from trees can cause disaster. Cold East winds can do a great deal of damage and where possible, protection should be given by larger shrubs. Droughts cause problems most springs and lime free water should be available to keep the peat moist and the atmosphere cool, otherwise the peat may become dry, and the mosses die, allowing the blocks to disintegrate. Heavy pounding of the peat when using water direct from the hosepipe should be avoided. Always try to water using a light spray for best results.
Peats and their supply
Top spit, fresh cut, wet peat blocks are ideal but difficult to obtain anywhere in the UK. A local supplier may be willing to supply wet blocks in a few areas of the country. For many people, the only feasible way of obtaining blocks, was to buy fuel blocks and then soak them in dustbins (a difficult job) for several days. Unfortunately today many of the blocks offered are reconstituted from loose peat and are not so usable especially long term. Ideally, peat blocks should be at least 9 inches (22.86 cm) by 18 inches (45.72 cm), but the more readily available fuel blocks can be employed with equal success.
A web search will reveal a small number of suppliers who are still able to offer hand cut blocks that can literally be delivered to your door! Coir blocks are also offered but are not practical for wall building. Other alternatives to consider are natural timbers, and rock or stone to retain a medium made from soil and other improvers such as leaf mould. Here is an interesting article on peat cutting http://sianthom.blogspot.co.uk/2013/06/the-tradition-of-peat-cutting-part-three.html. There are a number of alternatives such as using branches from trees, to homemade hyper-tufa made from sand, cement, and peat alternatives such as forest bark.
Construction
The peat garden should give an impression of fissured, gouged moorland having rounded rather than angular terraces and walls. Unlike a rock garden, a peat garden is not dictated by size of stones. The blocks can be cut to size and shape. Removal of perennial weeds is very important, and should be carried out before construction commences. 
Howard building a peat garden at Clacks Farm circ 1986
After the site has been satisfactorily shaped and contoured, the peat blocks can be laid. In order to obtain height, they may need to be bonded like bricks in a wall and have a slight backward lean to prevent them from being dislodged. 'Walls' should be allowed to flow, rising and falling with the contours. Where necessary, blocks can be cut to shape using an old panel saw. As the walls are constructed, a mixture of peat and soil should be packed in behind the blocks, so leaving no air spaces. Stepping-stones can be laid in the terraces to facilitate weeding and other cultural operations, and also to provide a cool root run for some genera. When construction is completed, the whole area can be given a thorough watering and be allowed to drain and settle.
Planting
Careful thought must be given before selecting plants. The environment provided by a peat garden is suited to a very wide range of plants, but first one must consider plant forms. Shrubby material will provide shelter from winds, evergreens provide shelter and form in winter. Herbaceous plants and bulbs provide a break from shrubby material.
Creeping and mat forming plants can help keep down weeds but must not be invasive. Any plants selected must be decorative and “desirable”. There is a tendency to over-plant with shrubby material, it must be remembered that in time small shrubs can become large. Lilies etc. can be planted, with their feet in the shade with their flowers growing up into the sun. Smaller, often herbaceous plants, creeping or mat forming, should be at the front.
The soil should be gently firmed prior to planting but not over consolidated. Shrubs can be established in autumn but much of the herbaceous material is best left until spring. Many plants are surface rooting and extra attention must be paid to correct planting depth, which is then followed by a generous watering to settle them in.
Maintenance
The only tools required for maintenance will be a hand-fork and a pair of secateurs. Generally it is only a matter of weeding, clearing up debris, twigs, etc., pruning, dead heading and seed collecting if required. Seed production is at the expense of stature and therefore should be avoided unless the seed is needed. Top-dressing is very important, due to the processes of nature, erosion etc. A thin layer of peat or similar material should be applied, preferably in the spring together with the slightest dusting of fertilizer. Many creeping plants can become rampant under ideal conditions, and therefore it may become necessary to control their size by pruning. If a choice plant is becoming overcrowded, it is often the best policy to remove surrounding "second rate plants".
Autumn Work
The peat garden can be a blaze of colour in the autumn with Gentians, berries, foliage effects etc. However, the results of fallen leaves from nearby trees on the smaller plants can be disastrous, being smothered by the large soggy leaves. The removal of the fallen leaves appears to be a never ending job but is rewarded when “difficult” plants come into growth the following spring. Some plants, such as Asiatic Primulas may require overhead protection against moisture collecting in the resting buds.
Plant types
It is impossible to draw up lists of "definites" or "musts", as there are many variables such as soil type, rainfall, amount of shade, and even the supply of plants. Not all plants enjoy the environment provided by a peat garden, but members of the following families are most responsive to such conditions: ‑ Ericaceae; Liliaceae; and Primulaceae.
The majority of Ericaceae are woody shrubs, such as Rhododendron, Cassiope, Andromeda, Chamaedaphne, and Enkiananthus. The family Liliaceae contains many beautiful bulbs that fit in well with shrubby plants. Most are deep rooting and resent disturbance. In Primulaceae are many unusual Primulas and Primula like plants such as Dodecatheon and Cyclamen. There are also other valuable contributions from members of the Ranunculaceae, Saxifragaceae, Gentianaceae etc. all of whom revel in the peat garden environment.
Ericaceae
Andromeda
Arctostaphylos
Bruckenthalia
Bryanthus
Calluna
Chamaedaphne
Daboecia
Enkiananthus
Epigaea
Erica
Gaultheria Kalmia
Ledum
Leiophyllum
Menziesia
Paris
Pernettya
Phyllodoce
Rhododendron
Vaccinium
X Phyllothamnus
Liliaceae
Bulbinella
Clintonia
Disporum
Erythronium
Fritillaria
Helonias
Lilium
Liriope
Nomocharis
Notholirion
Polygonatum
Smilacina
Tricyrtis
Trillium
Primulaceae
Cortusa
Cyclamen
Primula
Dodecatheon
Omphalogramma
Members of Other Families
Adonis
Arisaema
Arisarum
Arum
Asarum
Astilbe
Boykinia
Calanthe
Calceolaria
Codonopsis
Cornus
Corydalis
Cyananthus
Cypripedium
Epimedium
Fothergilla
Galanthus
Gentiana
Hacquetia
Hylomecon
Incarvillea
Linnaea
Meconopsis
Mertensia
Orchis
Ourisia
Pachysandra
Paeonia
Platycodon
Polygala
Polygonum
Pyrola
Ranunculus
Romanzoffia
Salix
Sanguinaria
Saxifraga
Synthyris
Tanakaea
Thalictrum
X Heucherella
Further reading
Peat Gardens, Wisley Handbook,
The Peat Garden, Alfred Evans
Note both of these are out of print but second hand copies are available
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Howard Drury, Horticultural Broadcaster, Speaker, Lecturer, Writer, Adviser and Consultant
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The information given in this Fact Sheet is provided in good faith. It is however of necessity general information and advice on the topic. Howard Drury will not be under any liability in respect of the provision of such advice and information, and you are strongly advised to seek independent advice on any particular gardening problems or queries you may have, preferably from experts who can (when appropriate) inspect the problem before providing advice.
© 2022. This material has been produced by Howard Drury and must not be reproduced in part or full without the written consent of Howard Drury, Kings Heath, Birmingham, B13 0SJ.
JHD/18/01/2022
