It would be impossible to give any special instructions for any particular class of ferns, and there is no need of it. Those that make strong roots, such as the pteris, want root room and must be well drained. Those making surface rhizomes, as the davallias, do not want much depth of soil, but need surface room if large specimens are wanted.
It is generally conceded that in soil ferns are not at all particular. Atmospheric conditions are of far more consequence. A good fibrous loam, with a third of leaf-mold, will suit any of them, and many of the free growing kinds, such as nephrolepis, will flourish with a liberal addition of animal manure. Bone meal will help ferns if soil is thoroughly watered after repotting. Some growers of Adiantum cuneatum add about one-sixth of well rotted and sifted cow manure to their compost. Pot firmly but not too solid.
As before mentioned about temperature, few plants will thrive in a lower temperature than that of their native habitat so well as ferns. Species from the tropics, where in some localities the temperature would hardly ever be below 70 degrees, will do very well in our houses if not below 55 degrees. Growers of Adiantum cuneatum or A. decorum, who grow houses of them for the market, sometimes as pot plants, but more often for the cut fronds, will, I am aware, keep them higher than 55 degrees. Cuneatum will pay best when grown in a high temperature, but should be well matured before sold or it will soon wilt.
Watering ferns does not need any great skill. All evergreen ferns, and we grow only those, require plenty of water at all times, but less in winter, when all ferns take a partial rest. We have had young men tell us that at "their establishment," where the A. Farleyense was well grown, they have seen repeatedly Jack Jones standing with the hose and giving the Farleyense a good syringing. It must have been on the morning of bright summer days.
Almost all ferns are found as undergrowth in forests and woods, and are shaded by the trees above. Ferns want subdued light, but not a heavy shade.
The ideal conditions for all the ferns we grow would be a house that could be shaded, say, by 9 a. m., and the shade removed at 5 p. m., but that great and most desirable convenience the commercial man has not yet obtained. Next to that is a north house, where light comes in, but not the direct rays of the sun. As we perhaps have neither of the above, then shade by degrees till midsummer, and remove gradually as winter approaches. Ferns will grow fast enough in a very shady house, but the fronds are weak and straggling. Plenty of water at the roots, plenty of moisture in the house, is needed, but do little wetting of the fronds; they don't need it.
One of the most important points to observe is to give the ferns a cool bottom. A bench with three or four 4-inch pipes under it is the worst possible place. A solid bed covered with ashes will suit them far better. If growing adiantum on a bench, let it be a deep one and well drained, and no steam or hot water pipes near it. Let the pipes be on the side, where they can have no influence on the soil. The bottom heat that is so congenial to most of our soft-wooded plants is misery to the ferns.
The healthiest lot of ferns I ever saw under glass was in the fernery at the Manchester (England) Botanic Gardens. Cool and moist, with water trickling over rocks, with the dicksonias in the center, and their great stems covered with platyceriums, you could fancy you were transported to a rocky dell of New Zealand. The most luxuriant ferns growing naturally were on the banks of the small river or inlet to Lake Chautauqua, N. Y., where the osmunda grew to the water's edge in rank profusion, shaded by the overhanging forest.
Few insects trouble our commercial ferns. Scale is often troublesome to large ferns. Old fronds, if badly affected, are best cut off and destroyed, and washing the others with soap and nicotine is all you can do. Thrips will succumb to the fumes of tobacco, but ferns don't like tobacco smoke, and it is much better to vaporize with nicotine extract. Do this at least once a week; it will also keep down aphis, which sometimes infests the young fronds of the adiantums and will do the ferns no harm. Wood lice, which often are known by that awful name of sow bugs, eat the tender shoots. A hollowed-out potato in which they will go to roost will catch thousands, or a mixture of Paris green and powdered sugar placed along the edge of the bench will destroy them.
The small white slugs are the worst enemy of ferns, and the adiantums seem selected as their own especial diet. The old remedy of placing cabbage or lettuce leaves on the bench or pots is sure to catch many of them, but they should be examined early every morning. The slugs are said to be very fond of bran, and if small patches are put on the bench here and there the slugs will revel in it and can be caught. Large growers of the maidenhair find that a light dusting of air-slaked lime on the plants and soil about once a month is sufficient to dispel any visitation of the slugs.
Since most of the above was written a new and distinct form of adiantum has been put on the market called A. Crowe-anum after Mr. Peter Crowe, of Utica, where it originated. The writer considers it the most useful of its class, and will displace cuneatum for its freedom of growth, splendid fronds and great keeping qualities. It is sterile and is entirely increased by division.
A few words on its culture may be a guide not only for this variety, but others of its class. Put five or six inches of loam on a well drained bench. The compost that I saw it flourishing in was similar to what was growing roses in another house. The temperature was 60 degrees at night, and no steam or hot water pipes beneath the bench. The small divided plants are placed on the bench ten inches or one foot apart and will last three years. They are then partly dried off, lifted and again divided. They are shaded in the summer. Air-slaked lime is used both on the fronds, on the soil of the beds and on the crowns of the plants, used most profusely, which not only keeps down the slugs, but the lime must act also as a fertilizer. Liquid manure was also freely used.