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.
This plant is really not a Spiraea at all, but nothing will make the market grower call it anything else. Its proper name is Hoteia japonica. Hundreds of thousands of plants are grown under glass for market every year from imported roots, although the plant is perfectly hardy and flowers well in the open air during the summer months. The plants are highly appreciated, not only because they are cheap and easily grown, but on account of their gracefully divided leaves, superb bushy habit, and erect pyramidal trusses of pure-white blossoms which stand well above the brilliant glossy-green foliage. Besides S. japonica another plant, called S. astilboides, and its variety floribunda are extensively grown. Of late years new varieties, called "Peach Blossom" and "Queen Alexandra ", with soft-pink or rose-tinted flowers, have made their appearance. They are charming plants, but they will probably never dislodge the white varieties from public favour.
HOTEIA (Spiraea) JAPONICA IN FLOWER, WITH ASPARAGUS SPRENGERI AND.
Photo. Chas. L. Clarke.
When the roots are imported from Holland and France, about September, they are chopped up and made to fit into 5-in. or 6-in. pots. Any old soil available is worked in around the roots, and in most cases no attention whatever is given to drainage. Very little soil indeed is used, as the roots practically fill the pots themselves. The plants are then placed in beds of ashes outside a greenhouse, or sunk in soil in any convenient place, the tops being a few inches beneath the surface. Plants may be had in bloom at Christmas-time, and right on during the season till Whitsuntide, after which the prices usually go down with a rush, and the plants are snapped up for the costermonger trade. Early plants require a temperature of 75° to 80° F., a very humid atmosphere, and abundance of moisture at the root. After Christmas less fire heat will suffice, but the plants will always require plenty of moisture, and as the spring advances watering becomes one of the most strenuous occupations. The plants grow with such extraordinary freedom that they require to be spaced out frequently to allow for proper development. It is by no means unusual to see a plant in a 5-in. pot occupying a space 2 ft. square, and yet sometimes such lovely specimens will only realize 3s. per dozen in market, and even less. At one time - thirty years ago - Spiroea japonica fetched as much as 42s. per dozen when brought in early in the season, but the modern grower must be content with from 6s. to 12s. per dozen for good stuff.
In these days, however, the grower is helped considerably by the retarding process. The roots of Spiroea japonica may be stored in a refrigerator for several months, and there may remain without harm when there is a glut in the market. When taken out, the plants can be had in bloom in from five to eight weeks' time, according to the season and the heat supplied.