Poinsettia (Euphorbia pulcherrima): Houseplant Care

Poinsettia is part of the large and diverse Euphorbia family that also includes some popular succulent houseplants. This small shrub is native to a seasonally dry biome in Mexico and Central America, though growers have developed the strains scaled down for seasonal use as houseplants.

Poinsettia (Euphorbia pulcherrima) became possibly the most popular of all holiday plants because of its mix of red bracts and green foliage. On more modern cultivars he tiny, inconspicuous flowers are surrounded by the large, colorful bracts that can be bright red, pink, or creamy white. Although poinsettias have been vastly improved, they are still temperamental as houseplants and require particular cultural practices to keep on after the holidays. 

The key points in caring for your poinsettia houseplant are adequate light, care in watering and stable temperatures, both day and night.  Inducing the plant to re-flower in subsequent years requires a strict seasonal regimen that can be difficult to adhere to in a home.

Light:

Poinsettias require bright but filtered sunlight each day. A south, east or west-facing window exposure will all work but ensure that the plant is close enough to the window to receive gentle light on its leaves. If you are keeping your poinsettia for more than one season, it can go outside during the summer in a position of partly shaded light. it is a tender tropical plant, so wait until the temperature is consistently above 50°F at night before placing it outside.

Temperature:

Poinsettias do best in night temperatures between 55° to 65°F and day temperatures between 65° to 70°F. Avoid warm and cold drafts from heat vents or windows as rapid water loss will result in wilt and leaf drop.

Watering:

Water the poinsettia thoroughly when the top of the soil dries out. Do not allow the plant to wilt, as this will cause inherent weakness and lead to quick demise. Water early in the day and use tepid water. Remove the run-off water from the plant's run-off dish or decorative outer container15 minutes after watering.

Humidity:

A relative humidity above 50% is preferred to successfully grow poinsettias and helps to keep the soil from drying too rapidly. That amount of air moisture can be difficult to achieve in a New York area home. Additional moisture can be provided by setting the plant on a tray of pebbles that is kept moist and/or using a humidifier. A simple hygrometer kept near the plant will help you to assess whether the humidity is in the target range.

Feeding:

Unless the plant is to be forced or grown from cuttings for future holidays, extra fertilization in unnecessary. For plants to be grown on after their first holiday season in your home, feed with a water soluble, all-purpose, liquid fertilizer twice a month during the growing season (April through September).

Re-potting:

Only when quite pot bound, move the plant into the next largest pot size. Moving the plant on to larger pots too quickly should be avoided as it encourages the plant to grow and become a large, leafy shrub rather than a compact houseplant.

If the plant is in a plastic pot move it into a new plastic pot; if it is growing well in a clay pot move it into a new clay pot. Pots should always have a drain hole. The soil mix preferred by poinsettia is equal parts sterilized houseplant potting soil and coarse builder's sand or perlite.

Propagation:

Tips of healthy side shoots that have not produced flower bracts make the best cuttings. These occur on plants that have finished flowering and then experienced a period of dormancy, in normal light but with minimal water. In April, the plant is reawakened by flooding it with water.

Make a 3 to 4" cutting just above a node, let it callus so that no more milky sap oozes and place it into a small pot containing a mixture of equal parts of peat moss and coarse sand or perlite. Keep it in filtered light and keep mix barely moist. Allow the top two-thirds to dry out between waterings. When rooting has occurred in about 3-4 weeks, move it into a pot of fresh soil-based potting mixture.

Inducing flowering in subsequent years:

Commercial growers subject their poinsettias to a strict regimen that is difficult to follow in the average home. All poinsettias are short-day plants--that is to say, flower bud and bract formation can be initiated only by an eight-week period of no more than 10 hours of light and no less than 14 hours of total, uninterrupted darkness per day. In addition, the plants are treated with a hormone that reduces stem length. The resulting short-stemmed plants crowned by large and handsome bracts are normally sold when they are in full bloom in early winter.

In order to induce a poinsettia into bloom for the next season, grow it in a sunny location with indirect light to build energy during the growing season. After all danger of frost is past it can be grown in a partially sunny location outside. You will need to acclimate it by taking it out gradually, not all at once. When the days start to warm up into the 50s and 60s you can put it out during the day and take it inside at night. Gradually you can leave it outside for longer periods of time. After a couple of weeks, you can leave it out all night, provided the nights don't get too cold.

Here are the steps to take to try to promote additional years of flowering:

• After the bracts have faded and fallen, cut top growth down to 1 - 2 inches from the base, and allow the potting mixture to become almost but not completely dry.
• When growth stops, keep the dormant plant at normal room temperature in bright filtered light, keeping the soil just barely moist; until April, then flood it with water. The plant, still in its old pot, will soon begin to grow again.
• Two ways of proceeding are then possible. You can take 3-inch-long tip cuttings from the new side shoots and root them to make new plants (see Propagation). Alternately, you can allow the stump of the old plant to develop an entire new season's growth.
• If you choose to use the old plant instead of taking cuttings, replant the newly growing old plant in fresh soil-based potting mix. Do not use a larger pot than the original one. Bigger pots merely encourage the rapid growth of lush foliage at the expense of flowers and bracts; the result is likely to be a huge plant unrecognizable as the desired poinsettia.
• Once the old plant is repotted, administer monthly applications of standard liquid fertilizer until September.
• After September, give the plant no less than 14 hours of total darkness per day for eight weeks (no easy task in most homes). The darkness must be uninterrupted each night or the buds will fail to form. To aid success, keep the night temperatures low and don't forget to expose the plant to light each day after the 14 hours of darkness. If it is difficult to avoid a light source at night, try completely covering the plant very gently with a black cloth or a large box from 6pm to 8am. After about 8 weeks, bracts and flowers should start to form. Then the plant is ready to be brought out into the light and treated as a houseplant.
• Because the dwarfing chemical used by professional growers is rarely available for amateur use, the resulting plant will be much taller than commercially produced poinsettias.

What to watch for:

Leaves will drop and flowers will wilt if the plant is kept too close to a heat vent or the draft from a window.

Do not allow the plant to wilt, as this will cause inherent weakness and lead to quick demise. Keep the soil moist, watering after the soil surface dries.