This section is from the book "The Florists' Manual", by William Scott. Also available from Amazon: The Florist's Manual.
In the days when short-stemmed flowers were used, the flowers of Gardenia florida were much prized. Flowers are often sent from the southern states, but by the time they reach our northern cities they are much the worse for the journey and often useless. There is at present a growing demand for these delightfully fragrant flowers and as the home grown flowers are so much finer than the southern article, we believe their culture will yet be taken up and specialized by northern growers.
The gardenia is a dwarf evergreen shrub. The double form of G. florida, called the cape jasmine, resembles the flower of a small camellia. They are propagated from side shoots of well ripened wood in strong bottom heat in December and January and kept rather close. In May or June they can be planted out in a coldframe or spent hotbed in six inches of good, light loam. Daily they should be thoroughly syringed to keep down mealy bug, thrips and red spider. During summer the leading shoots should be pinched once or twice. Early in September they should be lifted and potted into 6-inch or 7-inch pots, kept warm and close till they are well rooted in the pots. They can then be kept about 50 degrees at night, and a few plants started at intervals with more heat. It is difficult in our northern greenhouses to induce them to flower before February.
A method more adapted to the commercial man would, I think, be better especially in our northern cities.
Take young stock from 3-inch pots in the month of June and plant on benches in a light, sunny house. Let the plants be fifteen inches apart, and place each plant on a little mound where the soil is six or seven inches deep, and between plants let the soil slope down to three or four inches. They want such frequent syringing that the soil would be over-wet unless every care was taken to drain it.