Building Fern Rock Gardens
It is often stated that at least a third of a rock should be buried in the. This is unnecessary and a waste of good rock face. Provided that the lower edges of the rock are covered with soil after the soil has been well rammed underneath all round, and made solid so that it can be stepped on without moving it appreciably, that is all that is necessary. The top edges of outcrops should be more or less in one plane; the rocks should be buried just sufficiently to achieve this.
The ramming of soil under and around rocks is important; apart from making them firm, it fills up any air-holes which might be left to encourage mice to nest therein.
If the constructor wishes to incorporate pools in his rock garden they should be modest in size, as they would be no use for growing aquatic plants in the shade. These require all the sunshine they can get. For creating a moist atmosphere for the ferns the pool would need to have an extensive surface.
If the ground is a mass of tree roots, as is often the case in shady places near trees, before building up your mound cover the roots with overlapping sheets of corrugated iron, or plastic, or sheets of stout-calibre PVC sheeting, arranging this in a slope to shed off excess moisture. This will keep the tree roots away from invading your bed for a time, as they will do very quickly, given a chance.
Once the fern rock garden is well established it should stand some competition, with the help of annual topdressings.
I remember my grandfather had such a rock garden made of tufa, placed where the sun never reached it; and though over fifty years have passed I can still remember what a pleasant corner it was in mid-winter, planted up with rich green Polystichums and other ferns.
The higher parts of such a rock garden will be ideal for the many varieties ofvulgare. Generally the taller ferns should be planted on the lower slopes, Spleenworts in the crevices, and the Holly Fern, lonchitis, thrives in the deeper hollows between the rocks. In the lower reaches the Oak and Beech Ferns will run about happily and provide a carpet of delicious greenery. Hartstongues of all kinds delight in the lower rock crevices, arranged to contrast with a selection of those ferns mentioned earlier in the section.
The larger lower beds will make congenial homes for the many varieties ofsetiferum, especially the plumose divisilobes and acutilobes and others with more or less prostrate fronds.
The shadier wall garden makes an ideal home for many of the smaller ferns. Recently I constructed a limestone wall garden along one of my boundaries to accommodate my collection ofvulgare variations, and this has been a great success. The boundary wall runs SE. and NW., so that the new beds face NE. The soil in front of the wall was dug out and wheeled away for use elsewhere leaving a hollow about six inches below the ground-level. As the bed was five feet wide, it was decided to build two walls two and a half feet apart. The outer wall was built up dry about a foot above ground-level, filled up behind right back to the boundary wall with stone rubble up to the wall top.
The second wall then was built half-way back on the rubble foundation, dry, about a foot high, and this was also filled up behind up to the top with stone rubble. Both walls were built up a further nine inches or so, bedding the walling stones on fern compost, a mixture of leafmould, coarse grit and small stone, and were filled up behind with the same mixture.
Finally, I had two beds two and a half feet wide, the rear one some eighteen inches higher than the front one, and both containing fern compost nine inches deep over stone rubble.
The wall faces were planted as the work proceeded with various Aspleniums, Adiantum venustum, Phyllitis varieties,lonchitis and a few Ramondas and Haberleas for a bit of colour. The wall-tops were planted with varieties of Polypodium vulgare backed with Phyllitis scolopendrium crispum, and some Polystichums, and for added interest were interplanted with a collection of Petiolaris primulas, cyclamens, Daphne blagayana, hellebores, one or two prostrate rhododendrons, Cypripedium calceolus and C. regime, Primula Sieboldii, hepatica, double sanguinarias, Lilium Duchartrei. And various other bits pushed in from time to time. So far everything is thriving, except that I had some trouble with blackbirds scratching up the smaller plants. Such a wall makes an ideal home for slugs and snails, so regular dressings with slug-bait are put on — otherwise my cypripediums would be eaten flat.
Flat stones placed around the plants helps to prevent the blackbirds from doing too much damage.
The annual topdressing with gritty leafmould and bonemeal is routine procedure, reflected in sturdy growth.
The sunnier, drier parts of the rock garden need not be without their ferns. The Rustyback, Ceterach officinarum, will stand full sun if its roots are tucked away in a cool crevice where they can get back to moisture. In the warmer counties the North American Rock Brake, Pellaea atropurpurea, should succeed. Its handsome glaucous fronds with purple stems will stand full sun.
Some of the Cheilanthes might be tried in the warmer parts of the country, if they are planted with their crowns facing away from the prevailing wet winds. Their grey-green fronds with silvery reverse seldom exceed three or four inches.
The European Cheilanthes fragrans, the American C. lanuginosa and the New Zealand C. distans will all stand some frost, but they do dislike excessive wet and will require crevice planting in full sun with perfect. Protection with a suitably secured pane of glass during the winter months will prevent waterlogging of the fronds, which will hold moisture like a sponge.