This section is from the book "The Florists' Manual", by William Scott. Also available from Amazon: The Florist's Manual.
The annual zinnias are the only ones in which the florist is interested. With selection and culture, they are now among the handsomest of our annuals for the border, and in certain places a whole bed of them, in many shades, is very striking.
They are very easy to grow and need only the ordinary treatment given many other annuals, except that no frost must ever touch them while in a coldframe. Sow from the middle to the end of March, and when an inch high transplant into flats two inches apart. By the middle of April a coldframe is the right place for them. Plant in beds or borders after there is no danger of frost.
They are strong, rampant growers, and should have plenty of room; eighteen inches to two feet apart is close enough. They should have a well tilled piece of ground and will then stand our hot, and often dry, summers better than most of our summer flowering plants.
While the zinnia well deserves a place in the flower garden, it is the most unpopular of all flowers for even the cheapest sort of a bouquet. The poorest purchaser does not want them at any price. We have noticed this so often that we never cut them, however short of cheap flowers we may be. This proves that there is an unconscious taste for the artistic, even among the most lowly. The zinnia is so absolutely regular in form, stiff and formal, one flower being exactly like another, that the eye rebels against it. In a bunch of roses, carnations, or almost any other flower, no two are precisely alike, but the zinnias look as though they all came out of one mold. Then again, the stem is so rigid that while it is all right on the plant, it detracts from the flower when cut.
Grow zinnias to make your border gay, but don't offer the cut flowers to your customers. We raise quantities every year and sell the young plants from the flats at 25 cents per dozen.