This section is from the book "The Gardener's Monthly And Horticulturist V24", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
With very little care and simple treatment I have good success with these. I propagate in March ; as soon as well rooted pot them in two and a half or three inch pots, pinching them if they grow too lanky before planting out, which I do as soon as the ground can be got ready. They should be placed in a cool house or frame for a few days previous to setting out; frost won't hurt them if so treated. When they have grown about a foot, cut them back near the ground so as to get them stocky with as many branches as possible. Afterwards only pinch the strongest shoots every third or fourth week; it should be discontinued some time in August, according to the weather. Water when necessary; make a small basin around each plant to hold it. Lift and pot as soon as the flower buds can be seen. I get plants by this system having from thirty to fifty shoots. As soon as potted plunge in a tub of water, which I do with all plants taken up at this season. Place in the shade and sprinkle overhead as long as necessary. The large flowering varieties, like Empress of India, should be disbudded, leaving only one bud to a shoot. After two weeks use liquid manure till they are almost in full bloom, then discontinue - the flowers last longer. I grow about a hundred plants this way.
If there is a shorter way I would be very glad to find it out.