Poinsettias are beautiful plants. Getting that bright red color to reappear from year to year takes some planning, but with some work you can get your poinsettia to turn red in time for Christmas.
Poinsettia plants have tiny yellow flowers buried deep in the leaves. The part of the plant that most people call the "flower" is actually a group of specialized leaves called bracts. The bracts respond to certain changes in growing conditions by turning from dark green to bright red. Some poinsettias have bracts which become pale pink, cream-colored, or striped. These instructions will work equally well for all varieties of poinsettia.
Begin by taking proper care of your plant from very first day you have it; a healthy plant will be better able to withstand the stresses you'll be putting it through to force the color change.
Heat and Light Requirements
Place your poinsettia in a room that will stay between 65 and 75 degrees Fahrenheit. If the temperature dips below this overnight - even down to 60 degrees - your plant will still be okay; just don't leave your poinsettia in a part of the room that gets drafty, or near a radiator or in another spot where the temperature will fluctuate rapidly throughout the day.
Poinsettias come from Central America, and require a lot of light. South-facing windows are best, but you can place your plant in any spot where it'll receive direct sunlight for most of the day.
Water and Humidity Requirements
Poinsettias are very sensitive to overwatering. Check the soil in your poinsettia's pot before watering; if the soil is damp, wait a day or two to water your plant. When the soil surface is dry to the touch, pour in just enough water for it to start coming out of the bottom of the pot. Your poinsettia should never be allowed to sit in water, but it does need higher humidity than other plants to thrive. Get a shallow dish that's slightly larger than the poinsettia's pot. Put some small stones in the bottom of the dish and set the poinsettia pot on top of the stones. Pour water into the dish so that it comes up to just below the bottom edge of the poinsettia's pot; the stones will keep the pot's drainage holes from touching the water. Refill the dish with water as necessary.
Maintaining the above conditions will keep your poinsettia's bracts brightly colored throughout the holidays and maybe even into February or March. After Christmas, keep watering your poinsettia whenever the soil is dry. In late March or early April, it will be time to start the specialized care necessary to turn your poinsettia red.
Late March - Early April
Begin to gradually reduce the amount of water you give your poinsettia. Let the soil dry out before you give the plant water, but don't wait so long that the stem begins to dry out and shrivel. Aim for an extra day or so between each watering. After a couple of weeks, the poinsettia will have acclimated to this change in the watering schedule. Now you can move it to a cooler, darker spot in the home. The basement or a hallway that doesn't receive drafts is fine. It still needs daylight, but direct sunlight isn't necessary just now. The most important thing is to keep the temperature around 60 degrees Fahrenheit.
Late Spring - Early Summer
Prune your poinsettia in mid- to late May. Cut the stems back so they are between 4-6 inches high. Transplant the poinsettia into a slightly larger pot. Aim for a pot that is 2 to 4 inches wider and 1 or 2 inches deeper than the original. Use new potting soil. Water your plant well and place it in a window that receives direct sunlight, in a spot where the temperature will stay between 65 and 75 degrees Fahrenheit.
New growth will appear quickly; once it starts, it is important to fertilize your poinsettia every two weeks or so. Use a complete fertilizer, and follow the instructions on the package.
Late Summer - Early Fall
In June, you can move the poinsettia outside. Harden the plant off first by taking it outdoors for a few hours at a time for several days so it can get used to the conditions outside. Set it in a location that's partially shaded and protected from the elements. Maintain your fertilizing and watering schedule as before.
In July, cut the stems back by an inch or so. This will encourage the plant to grow bushier and more rounded. Cut the stems again in August, after the plant has had another round of new growth. After this final pruning, you can move the poinsettia back into its bright, warm spot inside your home. Keep up with the same watering and fertilizing schedule.
Late Fall - Early Winter
Start forcing your poinsettia's color change in October. This change is governed by the amount of light the plant receives. To turn your poinsettia red, you'll need to reduce the amount of light your plant gets to 12 hours or less each day. Put your plant into a closet or another completely dark space from 4 or 5 p.m. until 8 or 9 a.m. You can even put your poinsettia under a box, especially if the closets in your home allow light in through cracks in the door or if the closet where your poinsettia is will be opened throughout the day.
When your poinsettia isn't being given this dark treatment it should go right back into the same bright, warm spot where you've been keeping it. Stick to the same watering and fertilizing schedule as before.
At the end of November, return your plant to its sunny spot for the remainder of the holidays. It should have brightly-colored bracts and a few small flower buds. Stop fertilizing the plant in early December but continue watering it on the same schedule. Your plant is now ready to take center stage on your holiday table or mantel - just make sure it gets plenty of sun and water throughout the holiday season so it'll be healthy for next year!