MOISTURE IN HOTHOUSES.

Globe, Volume XXII, Issue 1996, 17 July 1880, Page 3

MOISTURE IN HOTHOUSES.

["Field."]

A very considerable alteration in the practice of damping hothouses and syringing plants has taken place in reoent times. I can remember, not so long ago, when it was the custom to keep fruit and plant houses dry throughout the day, or a part of it, and then shut up as soon as the sun heat would permit, and saturate everything with moisture; and this was followed by repeated damping until the last thing at night. I once saw an orchid house in which the hot-water pipes were double-wrapped with frigi domo, on which a perforated lead pipe discharged a constant trickle of water, causing a continual steam to ascend into the atmosphere. This was not so very objectionable on fine dry days when air -was admitted, and the pipes were not very hot, as it helped to keep the temperature down, and obviated the necessity of giving too much air during the keen bright days of early summer, in the tame way as damping the floors and paths does; but at night, when firing commenced, the condensation was dreadful, the moisture running down the cold glass roof in streams, or dripping upon the plants, which were always drenched. For these reasons, the frigi-domo wrapping was eoon discontinued. I am not sure that Xiindley's assertion, " that the more one heats and damps a hothouse, the drier it becomes," is quite true ; but it may be doubted if evaporating troughs of any kind are a necessity in hothouses at night. For my own part, I rather regard such appliances with disfavour, except under exceptional circumstances, and I question if "shutting up," with such copious eyringings and drenchings as are commonly practised, is right. Many, lam aware, advocate such practises, and can point to their success as cultivators in support of them; but still that does not prove their practice correct. Gardeners have abandoned many practices that were once considered essential, and there are probably others that will meet the like fate in time. I do not suppose that in tropical countries—even among steaming and malarial marshes—anything like the close, clammy atmosphere which can be felt in an orchid house when shut up on an afternoon is ever experienced. So far as I have read or have been informed, the air in tropical swamps and forests, though saturated with moisture held in suspension, is still dry, as we reckon dryness ; and this condition of things can be imitated in hothouses by damping pots and shelves, &c, during the day and while air is admitted freely. "Shutting up" must necessarily be practised to some extent, in order to Bave sun heat; but there is no necessity for closing the ventilators altogether, or of shutting up suddenly at any particular hour. Air should be admitted to all kinds of plant structures gradually, and reduced in the same way to the minimum, and moisture given and withheld in the same way. If the filanta are syringed overhead at about three or our o'clock on an afternoon, the moisture disappears from the foliage in about half an hour, as if it had never been; nor will it lie on the foliage of plants under glass, unless the temperature is allowed to fall to nearly the dew point—a thing hardly practicable under glass.

If such a thing were practicable as to have a donble glass roof at night, and a single one in the daytime, we could then imitate nature, because the moisture would naturally condense on the plants at night; but the single glass roof prevents this. Double glazed roofs were a good idea, but they will not do in the daytime because they shut out as much heat as they conserve, or more. The only practical substitute which we can at present employ for a double roof is a dry woollen or hair covering, supplemented by as low a night temperature as may be safe. It is, however, seldom desirable to let the pipes get quite cold in an orchid house, for example, as the air is then apt to stagnate. A very little heat in the jfe pipes renders it buoyant; but during a spell of fierce sunny weather little danger need be apprehended from cold pipes. If I remember correctly, Mr Boyd, the horticultural builder, informed us some time since that he was erecting a conservatory in the neighbourhood of Dublin, so constructed as to permit of the double roof being used at night only, or when needful. Perhaps we may hear by-and-by how this arrangement acts. Reverting to the subject of damping r.gtiin, I think for an evaporating surface nothing beats a well-sprinkled path or soil border. It is such as these I depend on almost exclusively ; but I do not like Hag paths, as they soon dry up, and while wet they are uncomfortable to the feet. Nothing beats iron grating, and it is far more ornamental, and quite as cheap in the end. In one long plant and orchid house here I have tried white Derbyshire spar put through a half-inch sieve for a path, and it suits admirably. The paths are edged with slate, and about a couple of inches of the spar laid on a firm bed of clean cinders. The spar is now as hard and firm as a macadamised road, and white and elean-looking. It carries no pools of moisture, and can be whisked over with a hair or whalebone brush in a few minutes. Underneath the shelves is a border planted with Lycopod and Fittonia; and in camping the man runs round the path and the border with a pan and a broad rose, and this is all the damping the house gets. More moisture is spilled throughout dry sunny days than at anyjother time.