This section is from the book "The Gardener V3", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
THE culture of Orchids is every day becoming more and more popular, and in many cases, we may add, more and more successful. Yet there is still remaining in numerous instances ample room for further improvement, and our present object is to suggest the direction whence more satisfying results are to be obtained. It is now pretty generally ceded by all good cultivators that the night - temperature of plant-houses should be lower than during the daytime. Nature all the world over cools down her temperature after sundown; and even in the tropics, near the line, there are altitudes of a few thousand feet at which, during clear nights, radiation is so great that at daybreak one's teeth chatter, and a fire is the greatest comfort one can have. My own experience of Orchids, under the most variable of conditions both abroad and at home, leads me to say that, even for the hottest of lowland East Indian and African species, a high temperature and an airless condition during night is far from being as beneficial as is by many supposed. Everyday practice has shown to me very clearly, and I doubt not but that the idea has occurred to others also, that those Orchids are most permanently robust and healthy which have been gradually and carefully inured to a wide range of temperature.
That this is true of men and other animals is a well-known fact. To illustrate my meaning I will take Phalaenopsis grandiflora as an example. In hot summer weather, when growing, the thermometer during bright sunlight may run up to 110° with advantage, provided the plants are moderately shaded; while, during winter nights, I never feel the slightest anxiety when the thermometer has not descended below 48°. In May, during hot days, the thermometer may run up to 95° or 100°, and at night descend to 55°, without any damage - indeed, as I think, with advantage - and a range of 40° in twenty-four hours is a very large one. The usual plan is to keep Phalaenopsis in a very equable temperature, never lower than 60° at night at any time during the year; and surprising as it may seem to many, it is to this uniform system of temperature that I attribute the numerous failures to cultivate Phalaenopsis grandiflora in a really satisfactory way. It is so coddled, so enervated, so to speak, by a uniform high-pressure kind of temperature, that, just as man himself does under like conditions, it breaks down in health gradually, but none the less surely, simply for want of that bracing exercise of all its normal functions which a wide range of temperature within certain limits assuredly gives.
Air and moisture must of course be credited with their share of the work in all well-developed plant-growth, and for no plant is air more essential than for the before-mentioned Phalaenopsis. As an instance of this, I may mention that all last summer, from May until September, I had a plant of the Javan form of P. grandiflora, growing and flowering like a weed, on a shelf near the glass of an intermediate Orchid-house. When I say that at times from twenty to thirty-six flowers were fully expanded on this single plant at the same time, it will be understood that the plant is by no means a tiny one. Air was left on this house night and day all the time mentioned, and special provision for airing the Phalaenopsis was made by taking a pane out of the roof above the plant in an oblique direction, so that rain might not fall on the crown of the plant. Thus treated, the plant made three fine thick leathery leaves. A fourth leaf made its appearance. At this stage, towards the latter end of August, the autumnal rains commenced in earnest, and to save the flowers which hung under the opening in the roof, the glass was replaced, and the result was a leaf-growth larger than any of the other three, of a far fresher green colour; but owing to the want of air, the leaf never acquired its proper leathery texture, and, of all the leaves upon the plant, is the only one which became in any way blemished.
Really good plants of Phalaenopsis grandiflora are very rare when one takes into consideration the way thousands of plants are imported into Europe every year; and that they are thus rare is, I am sure, owing to a hot, equable, and comparatively airless temperature. In nearly every collection of Orchids I visited during the past autumn, I found five plants of P. amabilis and P. Schilleriana; but of P. grandiflora even presentable plants were very rare. From many observations, I am certain that a hot and airy day-temperature, and a cool, moist, and airy night-temperature, is most essential to the permanent wellbeing of this beautiful plant. High and dry night-temperatures for this and all other Orchids are most fatal. In its native habitat, P. grandiflora is exposed to winds for four or five months, the force and steadiness of which we have no idea of in our own land. Then for the same period the plants are deluged by nightly rains. I am most anxious on this point of nightly rains, because they are so prevalent in the tropics that one may be excused for thinking them especially beneficial.
The fact that Nature syringes and waters her plants most during the cool night-time is not sufficiently appreciated; but nightly rains after very hot days in the tropics are so common, that one must perforce notice them. The finest collection of Phalaenopsis I ever saw in my life was syringed every night in accordance with Nature's plan, and air was always left in circulation during the night. I wish it to be clearly understood that I do not recommend anything like cool treatment for Phalaenopsids. No amount of heat in the day-time will do them any harm; but heat and drought at night will do so most assuredly. These and many other tropical lowland plants must always have a high mean temperature, but a wide range is also desirable; and as I have endeavoured to show, air and moisture during the night-time are even more desirable for these plants than the hot arid atmosphere but too frequently maintained, especially during the cold winter months. Even during what is called the dry monsoon in tropical regions nightly dews are very heavy, and the plants recuperate themselves during the cool, moist night-time, "after the burden and heat of the day".
F. W. B.