The Greenhouse Management Floriculture

Plant requirements are the same in a greenhouse as they are outdoors; but the greenhouse, with its gradually evolving, automatic means of supplying conditions artificially, is becoming better and better equipped for plant growth.

For example, light, so necessary for photosynthesis, may be reduced in the summer by shading the glass with whitewash or shades, and in the winter electric light provides additional illumination. Temperature is automatically controlTed by thermostats regulating the steam or hot-water circulation through pipes; ventilation, by similar controls attached to the ventilating apparatus. By means of air conditioning, which is finding its way into greenhouse management, both humidity and temperature may be controlled during either the summer or the winter. (Cold water flowing over tight greenhouse roofs during the summer is, of course, the simplest way to reduce temperature and increase humidity.) In some instances typical home air-conditioning units will serve. Watering, fertilization, and cultivation are taken care of by soilless culture, so that uniformity of growth is obtained and considerable labor saved. With crops growing in soil, automatic watering devices are gradually coming into use in the form of tensiometers and subirrigation for potted plants. Thus in a modern greenhouse practically every phase of the necessary factors of growth may be regulated or will be as greater 4erfection in methods and equipment is developed.

Light. Since many plants grown in the greenhouse are indigenous to climates of varying nature, light regulation is necessary. In the winter time its inadequacy is the greatest of problems because crop maturity must be secured at that time. Artificial light provides the answer except that the needed high intensity is extremely expensive. However, many crops respond to very low amounts of additional light.

In the summer excessive amounts of light must be reduced to secure proper development, as in the case of Saintpaulia, Cyclamen, and various tropical foliage plants. To a lesser degree this is true of rose and carnation, where reductions of light serve to keep the growth soft and flower color of higher intensity.

Humidity. Because of the artificial conditions that obtain in the greenhouse, the air is usually too dry for the majority of crops, and regulation of humidity is needed. It is provided by keeping the walks wet, sprinkling them by hand or irrigating them by systems that throw a 'fine mist on them or in the air. Humidiguides make it possible to determine the relative percentage of humidity, and such instruments should be employed where automatic regulation is not yet practiced. Crops vary in their humidity requirements, which should be learned if perfection is to be attained. For example, rose, gardenia, and orchid need relative humidities ranging, especially -during the warm seasons, whereas carnation, stock, and the various succulents grow much better. Regulation of humidity is likewise essential in the control of various bacterial and fungous pests as well as in fumigation and spraying practices. The most common and universally used method of humidity increase is syringing the foliage with water.

Moisture. Regulation of moisture in the soil is extremely important when plants are grown in the greenhouse. On the ability to water depends one' of the major factors of success, and here to a large extent the structure of the soil and the adequacy of drainage enter in. With perfect drainage (in most greenhouses it is not adequate) and a uniform supply of moisture, good growth is assured, provided all other factors are controlled. The actual practice of watering usually depends on heavy drenching to provide the moisture and a subsequent partial drying to provide the air. Various "breakers" are attached to the hose to reduce pressure without sacrificing volume and thus supply the moisture without packing the surface of the soil. Crops vary considerably in their soil water requirements, so general rules cannot be made. Furthermore, it is important to realize that in bench-grown crops spot watering after planting young or dormant plants is essential. Spot watering refers to the application of moisture to the area around the plants and not the whole bench, until such time as root extension spreads into the soil between the plants. Plants with large root systems require more moisture than those with small ones. Those with fine roots demand less moisture than the coarse-rooted kinds. For example, rose requires more moisture than carnation, saintpaulia less than hydrangea and cineraria. Dormant plants like bulbs, hydrangea in the winter, and rose in pots started for Easter are provided with small amounts of water at first until root action develops. The season of the year likewise has its effect; obviously, during the winter waterings are fewer than in the spring and summer.