Growing Ferns in Cold Frames
Where there is no cold house available, and no suitable garden space, often there is room for one or more cold frames. Many interesting and beautiful ferns can be grown in these structures. The frames preferably should be placed overif the ferns are to be planted directly therein, but if they are to be put on a flagged yard or on concrete they are best used to accommodate a collection in pans and pots, plunged in ashes or sand. This is because a frame set on concrete and filled with soil would not have adequate , whereas one filled with pot plants in ashes will drain better.
Where the underlying soil is reasonably good and well drained it is enough to fork in extra leafmould and coarse grit, but if the natural soil is very poor or very heavy it is as well to remove it to the depth of a foot or so; then, breaking up the bottom thoroughly, add six inches of broken stone, broken bricks or similar material spread over the frame bottom; cover this with a layer of rough fibrous peat or similar material to prevent fine soil washing down, and then fill up with six to nine inches depth of good fern compost.
In bright sunny weather shading may be necessary and the best method of providing this is to make lath frames which can be removed easily in dull weather. A lath frame can be made very easily by nailing together pieces of timber, one and a half to two inches square section, to make a rectangular framework just the size of the frame lights.
Plasterer’s laths are now nailed to the frame, leaving one-inch gaps between each lath, until the whole framework is covered. Treated with a suitable wood preservative which is not injurious to the plants these lath frames will last for many years.
Nowadays plastic shading; is made which will roll up and down, or it could be attached to a framework similar to that described above, for it is desirable to remove the frame lights altogether in fine weather, leaving the lath or plastic shading in position, and this will require the shading to be kept rigid.
Good ventilation is important at all times. Anything like a close stuffy atmosphere must be avoided by providing means of keeping the frames propped up a few inches.
Suitable ferns for frame culture are those of moderate stature which will not grow above the sides of the frame, and include the Adiantums, Aspleniums, Cryptogramma, Cystopteris, Blechnums, Cheilanthes, the dwarfer Athyriums, Polypodiums and Polystichums, and the many dwarfer varieties of Phyllitis scolopendrium.
Care should be taken to avoid constantly wetting the fronds when watering, especially the Aspleniums, whose fronds will turn black and rot when kept too wet.
Maintenance consists chiefly in keeping the frame tidy, removing weeds as they appear, removing dead fronds, and giving more room to varieties which begin to encroach upon one another. An annual top-dressing as advocated for ferns planted out in the open or under glass is repaid by healthy growth and good-coloured fronds.
In very bad weather, or when smog appears, the frames should be closed down until the weather improves, when air should be given once more. After fog it is necessary sometimes to wash down the glass to remove deposits of grime which would prevent sufficient light reaching the plants. The frames described are the traditional type, but, of course, there are all manner of structures on the market nowadays which can be used. Many are easier to manipulate, but the same principles apply to all.