This section is from the book "The Florists' Manual", by William Scott. Also available from Amazon: The Florist's Manual.
This is one of the many hard-wooded evergreen shrubs that we get from the Southern Pacific islands. The species we import is M. robusta, and its peculiar, terminal, densely flowered spike is so like in form to a bottle brush that the popular name is often suggested by people who have never heard it. It has been for many years grown as a cool greenhouse plant, but only within a dozen years have the Europeans been sending us the little, compact bushes that now arrive with our azaleas. The Belgians grow it in peat, as they do most hard-wooded plants, but it does very well in good turfy loam with a fourth of leaf-mold. It will root from the young growths in early spring, which can be planted out in good soil the last of May. But with tariff included we can get fine plants landed here at a cost that it would be impossible to grow them as good for the same money.
Metrosideros, the Bottle Brush.
You don't want a great many of them; about one to every ten Azalea Indica you grow. Plants in 6-inch pots, well flowered and fixed up with a red ribbon, do look novel and attractive, and a limited number find a ready sale.
When they arrive soak the ball and then pot firmly and put in a house at about 45 degrees. To bring them in for Easter you must watch them and gradually give them more heat, but not suddenly. Freshly imported plants if forced in much heat, as you can an azalea, will shed their flowers.
Plants unsold the first spring will be much better and more satisfactory the second year. At the end of April cut them back to within an inch or two of the old growth and put them into a good heat and and keep syringed. They will make a bushy growth with a number of shoots. Early in June plunge them out in the broad sun, well covering their pots, and in the hot weather don't let them suffer for water. In July or earlier mulch the surface of the pots with an inch of half-decomposed cow manure; this will add greatly to their robustness. Bring in before any danger of frost and keep in a temperature of 45 degrees; warmer if you want them earlier than Easter. These will be far better plants and be much more satisfactory to the purchaser than the newly imported.