The liquid from farm-yard manure, or from a stable, should be avoided, as its strength cannot be known; sometimes it is very weak, and at others fatally strong. A large tub with liquid manure made of cow-dung, and in which a coarse bag of soot has been sunk, is a safe manure for any plant, and if properly diluted can do no harm to plants requiring such a stimulant.
Terrestrial Orchids such as Calanthes and Phaius can scarcely be grown to their best without a liberal application of this, or some other manure known to the operator to be safe, during their season of growth. Cymbidiums, Zygopetalums, Peristerias, and other strong-growing Orchids have also been treated to weak liquid manure from the commencement of growth until the flowers expanded, with advantage so far as evidence is available.
An occasional watering of liquid manure, or slight sprinkling of guano, may be given beneath the staging in the evenings during the growing season.
The structure of the roots of Orchids does not favour the idea that they are suited for taking up stimulating liquid in the manner common to fibrous-rooted plants.
On the general question of the use of stimulants in Orchid culture many clever men have carried out experiments. The late Dr. A. H. Smee went into the question, basing his experiments on the chemical constituents of the plants themselves, which is not an infallible guide.
The late Norman C. Cookson carefully studied the subject, and he recommended for experiment the following formula:—
| Potassium nitrate (saltpetre), | 3 oz. |
| Ammonium phosphate, | 2 oz. |
Dissolve in a three-gallon jar of soft water, and when watering growing Orchids, or those perfecting their flowers, add one ounce of the solution to each gallon of water.
Again it must be urged that those experimenting with manures must do so only on growing plants, and when growth is completed it must be stopped. No Orchid grower should undertake such experiments without first obtaining his employer's concurrence.