It is possible to keep a poinsettia growing until the next season, however you will need to follow these tips to be successful:
- First, avoid over-watering your poinsettia. Allow soil to dry out a little between waterings. Consistently wet soil can be a killer.
- At the end of April or early May, when the bracts (colored leaves) age and begin to turn a muddy green, cut the plant back to about 8 inches in height. The amount you cut from the top will depend on the shape of the plant. After you cut the plant back, it will look bare. This is not the plant's most attractive state, but by the end of May you will see vigorous new growth as the plant develops more lush green foliage. Keep the plants near a sunny window or place them outdoors where they will receive a good amount of sunshine.
- Continue to water the plants regularly during the growing period. Fertilize every 3 to 4 weeks throughout the spring, summer and fall. Use a well-balanced water soluble fertilizer mixed at half-strength.
- Around June 15th you can transplant your poinsettias into larger pots, about 2 to 4 inches larger than the original pot. Fill empty space in the new container with a professional potting mix. Immediately after transplanting, be sure to water thoroughly.
- Starting October 1, the plants must be kept in complete darkness for 14 continuous hours each night. Moving the plants to a dark room or placing a large box over them can accomplish this. During this period, the plants require 6 to 8 hours of bright sunlight and night temperatures between 60 and 70 degrees F. If the temperature is too high or too low, the setting of the flower buds may be delayed or halted. The blooming process may also be delayed or disrupted by any stray light that may shine near the plants during the critical darkness period. Keep this up for 8 to 10 weeks for full color development.
If this sounds like a lot of work, it is...and it certainly gives us a healthy respect for those who commercially grow poinsettias!
If you did everything right, the plants will naturally come into full bloom during November or December, depending upon the flowering response time of the particular variety. This can be tricky to do outside of a controlled greenhouse environment, because any stray artificial light, such as that from a street light, pool light or household lamp could delay or halt the re-flowering of the plants.