This section is from the book "The Gardener's Monthly And Horticulturist V18", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
The well-known Astilbe japonica, which is, perhaps, better known as "Spiraea japonica,"' is eminently valuable to furnish greenhouse flowers early in the spring, though it is a cheap hardy herbaceous plant. When forced slowly in a damp pit, close to the glass, it is one of the loveliest plants in the world, and well worthy to be made a feature of in any private garden where beautiful plants are valued by some other scale than their money value in the market. They should be potted in September' or October, in a mixture of turfy loam, leaf-mould, decayed manure, and sand, and started in a temperature of about 55°. From this allow the temperature to rise gradually to 75°. They should be supplied liberally with water when growing freely, and may be placed in pans of water to advantage. It is a matter of no consequence what sized pot is employed, but for ordinary decorative purposes, five, six, and eight-inch pots will be most serviceable; the two former for the drawing-room jardinets, and the latter for the conservatory. Strong clumps ready for forcing may be purchased at nurseries and seed houses. Those who prefer growing them for forcing in after years may do so with but little trouble.
Early in May or June they may be planted out in an open quarter previously well prepared for their reception. They should have two or three liberal waterings and a mulch of short litter, or partly-decayed leaves, placed between the rows if it can be spared. They will then require no other attention, and by the autumn will have formed strong crowns and be in grand condition for forcing. If considered desirable, they may be divided into single crowns in May, each of which will form a nice little plant by the end of the summer. Those who have not convenience for forcing may have a fine display early in the season by simply keeping them in the greenhouse from the time they are potted until they come into bloom. Of course they should be placed in an out-of-the-way corner until the young growth begins to push, and then they should be placed in a position near the glass.- Journal of Horticulture.