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 Poinsetta is a little difficult to grow satisfactorily in pots, being somewhat irksome to maintain the proper degree of moisture, which seems requisite to its well being. How we have obtained the most satisfactory results with least trouble, is to plant them out in the open ground, in May, or as soon as there is a fair prospect of settled weather. When the weather begins to get hot and dry, we give them a good mulching of well-rotted manure, if procurable, if not, with short grass, which keeps the ground cool and moist. By the end of the following month, if they have been growing vigorously, the young shoots will have attained the length of fifteen to eighteen inches. This we cut back to four eyes, from which it started in May; in all likelihood those four eyes will push simultaneously, which rarely happens when grown in pots, or nipped off' as soon as they have made four or five leaves. The strongest of this growth is cut back again about the first week in August - cutting with a view to equalize the flow of sap and form a compact head. Near the end of this month, select a cloudy day, and, with a spade, cut around the plants thoroughly, not underneath. Pack the soil firmly around them again, and replace the mulching.
The distance from the stem they require to be cut must be regulated by the size of the plants and pots you intend they shall occupy. This should be done three weeks previous to their removal. In that time they will make numerous fibrils, which can be removed without injury-which is very essential to successful transplantation. After being lifted and staged for some time they require to be carefully shaded, and, if kept in a close, humid temperature of 65°, they will lose few of their leaves, will quickly become established, and, in the course of six or seven weeks. We opine that, under good cultivation, as a winter flowering decorative plant it has few compeers. Some, however, prefer growing them in pots, and assert they should not be cut back, as it impairs the size of the bracts. Recently we saw an illustration of this method at a commercial establishment, credited with having well-grown plants. In outline they reminded one of the common Sumach (Rhus glabra), as seen in the fall of the year - shoots over three feet in length, nude, except very near the top.
Tortured in this way, it is, undoubtedly, more queer than beautiful.