This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
These are generally grown to supply cut flowers, which at all times, but especially during the winter and early spring months, are in considerable demand. Plants are readily struck from cuttings, taken any time during the growing season, and inserted in a moderate bottom heat. For cut blooms, Gardenias are generally planted in borders, as if long in pots the tips of the shoots are apt to turn yellow, and greatly depreciate the crop of blossoms. In planting out Gardenias effective drainage must be ensured, and the bulk of the soil should consist of good turfy loam. As Gardenias are pronounced surface rooters, space should be allowed for an occasional topdressing. With ample drainage, water may be freely given, both at the roots and overhead. Insect pests may be kept down by syringing with paraffin emulsion. Liquid manure and soot water combined is one of the best stimulants that can be employed. To obtain flowers in the depth of winter a minimum night temperature of 60° F. will be necessary. Ten degrees less may, however, be safely allowed in the case of plants required to bloom in early spring. In packing the flowers it must be borne in mind that they are very easily bruised, for which reason they are best packed in shallow boxes in a single layer, the box being lined with wadding, slightly damped, and covered with tissue paper.
When the soil is badly drained, and perhaps also too rich with humus and artificial fertilizers, and the temperature is kept too high, the roots of Gardenias are often afflicted with Eelworm (Heterodora radicicola), and become irregular masses, useless for absorptive purposes. The soil should be well drained and dressed with lime or basic slag. [W.T].