Q: I kept last year's Christmas poinsettias alive and well this summer. They are big and very beautiful, but very, very green! Incidentally, they were not a true red poinsettia; they were more of a pink color. What do I do now? I think they have to get some nights and days of darkness.
A: Congratulations! You are now a poinsettia grower. You've taken excellent care of your plants, and now, with a little more work, they will reward you with blooms. But don't expect them to be as large and glorious as plants you bought last year. They will be smaller but just as beautiful, more like the wild poinsettias from Mexico.
Poinsettias are light-sensitive plants that time their blooming to the hours of daylight and darkness. If you interrupt the pattern, the plants may still bloom, but on their own time — maybe for Valentine's Day or Easter! You must now be in charge of timing their light accurately, and you must start the dark-light process now for blooms in mid-December.
Plants should be inside now and thriving on a warm, sunny windowsill. Treat them as any other houseplant — keep them watered, watch for bugs, especially mealy bugs, and fertilize with your leftover tomato fertilizer to promote buds. Now comes the hard part: Poinsettias need to be put in total darkness for 12 hours out of every 24 hours on a regular schedule for the next eight weeks. No cheating or peeking!
Depending on the number and size of the plants — and your stamina — you can put them in a closet or a dark room, or you can cover them with an inverted sturdy box or a lightweight sheet. Each day, you must return the plant to the sunny windowsill and water and feed as usual.