THE COASTAL GARDENER:

Last year, about 41 million poinsettias were sold in the United States. They are the country’s top-selling and most popular potted flowering plant. It seems just about everyone has a poinsettia or two in their home and, as expected, several gardeners have been recently asking for specific advice:

How often should I water my poinsettia?

First, be sure to take off any decorative foil or plastic pot covers, or at least punch several holes in the bottom. Never let a poinsettia stand in water. For small plants in 4- or 6-inch pots, water them when the top inch of soil is dry. Larger plants can go dry a little deeper. With practice, you’ll be able to tell when to water by the plant’s weight. When you do water, be sure to be thorough, soaking the entire root system. Don’t just moisten them with a quarter cup of water added to one side of the pot; bring your poinsettias to the sink or outdoors and give them a thorough drenching, two or three times.

Why are my poinsettia’s leaves turning yellow and dropping?

When the leaves yellow and drop, nine out of 10 times it is water-related. The plant was standing in water, or it dried out completely for a day or two before it got watered again. A few days later the leaves turn yellow, droop and fall off the plant with the slightest touch. In a related scenario, the plant is getting only a little taste of water, applied sparingly to a portion of its roots, creating wet and dry spots throughout the soil, as mentioned above.

The balance of the time the cause of yellow, dropping leaves is the plant being by a heating vent or cold draft or the plant being mishandled at the store where you bought it.

My poinsettia is blooming and beautiful, but the leaves are curling and slowly falling even though they are not turning yellow.

The leaves will curl and fall off from a lack of humidity and dry indoor air, especially when the home is closed up and a heater is running. Increase the humidity by placing the poinsettia in a different location, near other indoor plants or above a tray of pebbles and water.

Are poinsettias poisonous?

Contrary to common misconceptions and lingering superstitions, poinsettias are not toxic. According to Poisindex, the primary resource used by almost all poison control centers nationwide, a 50-pound child would have to eat more than 500 poinsettia leaves to be potentially dangerous. For a few people with latex allergies, the sap from the leaves may cause skin irritation. Also, the sap should never come in contact with your eyes.

Can I plant my poinsettia outside?

Yes, but since poinsettias are tropical plants, wait until at least mid to late spring. When doing so, cut the plant back about halfway. Choose a well-drained and warm location in full sun or at least for two-thirds of the day. Poinsettias like lots of heat during the summer, but mild temperatures in the winter. In the ground, poinsettias get rather large and rangy, up to 10 feet or more. Also, the brittle branches can be broken easily in strong winds, so select a location in the garden carefully.

Can I grow a poinsettia from a cutting?

Yes. In fact, if you want to grow a poinsettia as a garden plant this is the best way to begin. Modern poinsettias are hybridized for holiday performance, not garden vigor. Locate a thriving, well-established poinsettia growing in an older neighborhood and ask the owner if you can have a small cutting.

You will have better success rooting your cutting in spring or summer. Cuttings should be between 3 to 4 inches long with two to three mature leaves. Rooting hormones will increase your chances of success. Place the planted cutting in a bright location, but not in direct sunlight. Put the pots with its cutting inside a plastic bag to maintain humidity and prevent it from wilting. The brighter the light, without causing wilting, the greater the chance of success. After four or five weeks, the cutting should have developed a root system.

Should I fertilize my poinsettia?

You don’t need to fertilize a holiday poinsettia at all. Although colorful right now, poinsettias are dormant and not growing at this time of the year. Fertilizer will be of no use to the plant.

If you are growing a poinsettia in the garden, begin fertilizing it at the onset of new growth in spring. An all-purpose organic fertilizer, like Dr. Earth, would be fine. One of the deficiencies that poinsettias in Orange County sometimes show is a lack of magnesium. This is characterized by blotchy yellow leaves or scorched edges. Magnesium deficiency is prevalent in sandy soils, especially along the coast. Dr. Earth fertilizer should have enough magnesium in it to avoid this problem, otherwise a light application of magnesium sulfate (Epsom salt will do just fine) once in the spring and again in summer will correct the problem.

How can I get my potted poinsettia to bloom again for Christmas?

In horticultural jargon poinsettias are referred to as short-day plants. To start flower bud formation poinsettias need 14 hours of uninterrupted darkness every night for about for six to eight weeks. Because our nights in Orange County don’t lengthen to this point until early December, most poinsettias will not naturally come into flower until well after the holiday season is complete.

If you want to “force” a poinsettia to bloom for Christmas you will have to give it artificial 14-hour nights. On Oct. 1, begin giving the plant uninterrupted darkness for 14 hours every night, with no exceptions. The plant must be in total darkness during this time, no streetlights, night-lights, open and closed doors or light seeping under the edges and through the cracks of a cardboard box. A couple days before Thanksgiving, stop the daily treatment and the plant should come into bloom just about right for the holiday season.

RON VANDERHOFF is the Nursery Manager at Roger’s Gardens, Corona del Mar.