PLANTanswers: Plant Answers > Poinsettias and Mistletoe

POINSETTIAS AND MISTLETOE
by Jerry Parsons, Ph.D.
Horticulture Specialist, Texas Agricultural Extension Service in San Antonio

Poinsettias were originally native to Central America, so they enjoy a long, warm, sunny growing climate. Greenhouse operators find this relatively easy to accomplish, but the average homeowner may have a bit more trouble.

Did you know that this plant is really a large shrub in the tropics, growing to a height of 10-15 feet, sometimes more. You'd think a plant that size would be a blaze of color when it flowered, but interestingly enough, the larger the plant the smaller the flowers. Of course, there are more of them.

And speaking of poinsettia flowers, did you ever see one? You have to look closely. They are those yellowish-green structure in the center of the colorful bracts. Poinsettia bracts, like those of dogwood trees, are the highly colored leaves that develop around the flowering structure.

Have you noticed the improvements that have been in poinsettias the last 10 to 12 years- Growers in Ohio and California and with the USDA in Beltsville, MD, have come up with new varieties in shades of red, pink, white and variegated that hold their leaves and bracts for longer than the old varieties. At the same time, chemicals have been developed, are now in common use, that keep plant cells from elongating actively. The result is more compact plant bearing a normal number of leaves, but with these leaves coming closer together.

Did you know that a poinsettia leaf can "see daylight"? It takes a real plant physiologist to explain it, but simply stated the poinsettia will not produce flowers until the nights reach a certain length. If we turn on a light halfway through the night, we can keep the buds from developing.

Greenhouse operators use that trick when they want their plants to grow. To promote flowering, they pull a black shade cloth completely over the benches where the poinsettias are growing, to give them artificially long nights, 14 or 15 hours long.

Poinsettias, according to every old wife's tale, are poisonous to humanity. Such says recent research from Ohio State University, just isn't the case. While we wouldn't recommend poinsettia salad, there's no reason to keep them locked up in the medicine chest! It seems that this wild tale of toxicity began in 1919 with an unsubstantiated story of a two-year-old child of an Army officer stationed in Hawaii dying from eating a poinsettia leaf (bract).

Mistletoe IS A DIFFERENT STORY! The word mistletoe usually brings to mind Christmas festivities, and the pleasurable results of getting caught under the sprig of mistletoe. But did you know it is actually a pest on many of our landscape plants? Mistletoe is the most conspicuous parasite affecting trees in many areas of Texas. Hackberry and live oak are most frequently attacked. However, many other landscape trees can also harbor this flowering pest.

Parasitic seed plants vary widely in their dependence upon the host plant. The more independent ones are referred to as half-parasites. Mistletoe represents the extreme of this group, having lost contact with the soil and being dependent on its host for all water and dissolved minerals. It is, however, a chlorophyll containing plant, that is it has the green coloring matter in its leaves which manufactures the sugars and starches needed in its growth and development.

The mistletoe species most commonly found here in Texas produces clusters of perennial, green jointed stems on the branches and trunks of the host tree. The stems bear conspicuous green, leathery leaves which persist for several seasons. Nutrients and water are supplied from an absorbing system which develops in the bark and wood of the host plant. Flowers are born in the leaf axil and produce the familiar, translucent, whitish berries in late fall and early winter. An important fact to remember, especially when mistletoe is used for decorative purposes during the holiday season, is that the berries are very poisonous.

Within the tough outer coat of the berry is a single seed which is embedded in a sticky pulp. Birds feed on this sticky pulp and discard the seeds which stick to their bills, feet, or other parts of the body. in this way the seeds are carried to other trees or other branches of the same tree and deposited. when conditions are right the seed germinates, sending its root-like structures into the host plant and another parasite is developed.

Mistletoe frequently becomes so abundant in trees that control measures become necessary. For temporary removal of mistletoe, the parasite can merely be broken off. In due time, however, it will grow back. More lasting control can be obtained by removing the limbs on which the parasite is growing. No chemical is presently available to successfully control mistletoe without doing excessive harm to the host plant.

Cut all the mistletoe you want for the holiday season to reduce the amount in the landscape plants. Remember to keep the berries out of reach of small children. Most important of all, it is claimed by some participants that those caught under the mistletoe have a better chance of catching a winter cold than of catching a mate so be careful.