Growing Ferns under Glass
Over the years it has been fashionable to grow ferns in Wardian Cases, bottle gardens or the like.
If it is felt however, that there is not sufficient interest in the ferns themselves, there is no reason why a small pool should not be made of fibre-glass and used to construct a miniature landscape. One or two tinycould be installed — remembering the golden rule for cold-water fish: a gallon of water per inch of fish if they are to remain in good health. Or one or two green tree frogs could be kept very well in such a case, and they are amusing little pets and little trouble, and would not damage the ferns — much. But, of course, the introduction of any form of animal life makes the case less trouble-free.
I personally keep my Filmy Ferns in what is usually described as a ‘lash-up’, a temporary job which has lasted some years, as I never seem to find time to make a really handsome house-worthy case. I just took a shallow packing-tray about four feet by two, six inches deep, nailed uprights at t he corners and fixed top rails on these, to carry the roof. 1 stapled polythene sheet to the uprights, and made a polythene covered frame as it lid, and in this I have kept Filmy Ferns in perfect condition for months. They are grown in pans and trays for ease of handling, and need watering perhaps once a month. It stands out of doors in the shade of a building.
The Filmy Ferns are particularly suited to the case method of cultivation, as they need maximum humidity, and will not survive getting really dry — though I have found Wilson’s Filmy Fern a thousand feet up on the Devonshire tors. It was looking rather miserable, though.
The British species, Hymenophyllum tunbridgense and H. Wilsoni, and the very rare Killarney Bristle Fern, Trichomanes speciosum, flourish exceedingly in my case. The New Zealand Filmies, of which there are many species, the Prince of Wales Feather, Leptopteris superba, and Leptopteris hymenophylloides and the beautiful Leptolepia Novae-elandiae, all will thrive in a well-kept Wardian Case.
The miniature rockery can also accommodate the dwarf Aspleniums, which will make marvellous specimens if the foliage is not kept too wet, and the dwarfer varieties of the Hartstongue, Phyllitis scolopendrium, will make handsome plants. The dwarfer Adiantums too are well worth trying, but the larger-growing ferns should not be used, as they would take charge and soon get out of hand.
Large glass bell jars are very useful in the cold greenhouse for growing Filmy Ferns, though they are perhaps not fitting inside the home, but I have kept plants of Hymenophyllum and Trichomanes happy for months without attention, in pans under bell jars, the edges of which were pressed into the ground to maintain the humid atmosphere.
I have had one large pan of Hymenophyllum tunbridgense thriving in a shady corner of my mist propagating house for over two years, without any cover, the mist providing the requisite humidity. Of course, these ferns grow in the open air in Britain, but always in places where they enjoy high humidity, such as in reach of the spray from waterfalls or in woodlands in areas of high rainfall. I know a place in Lakeland, in one of the wettest valleys, where there is, literally, enough Hymenophyllum Wilsoni to cover a tennis court.
Quite recently I heard of a keen amateur fern enthusiast who had converted a whole basement window into a super Wardian Case, taking in the whole window as one side and constructing around it the other glass panels within the room. This proved to be most successful and a never failing source of interest, to friends and family alike, and a great stimulus to the youngsters to take a greater interest in growing things.
Another instance of a similar structure erected outside the house with windows opening into a living-room was built by a friend of mine. Through the case, being subjected to higher intensity of light out of doors, some form of shading had to be considered, and the temperature of the case was kept above freezing by means of a water tank heated by an aquarium heater thermostatically controlled. This provided warmth and humidity so that comparatively tender ferns could be grown. Some interesting problems arose concerning the optimum concentration of carbon dioxide required for healthy growth, and it was suggested that provision of material which would gradually produce CO2 assisted in maintaining the plants’ resistance to fungal attack.
Plants use up carbon dioxide during the day in forming foodstuffs within the plant, and exhale excess carbon dioxide at night, in the dark; but in a completely enclosed unit, as the plants grow in size the amount of free carbon dioxide in the container gradually diminishes, as it is used up in the formation of new tissues. When the carbon dioxide present falls below a certain concentration, growth becomes weakly and the plants more subject to fungal attack.
This fact is the basis of modern glasshouse techniques in which the carbon-dioxide concentration is artificially maintained.
Where a fern case is artificially illuminated after the hours of daylight the plants continue to absorb carbon dioxide while the light is on, reducing the dark period when they exhale it again.
This state of affairs is a good basis for the suggestion that some form of animal life, such as green tree frogs, be introduced, as animals exhale carbon dioxide as a harmful waste product of animal metabolism.