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Q: When planting a rooted dieffenbachia, is there anything that can be done to keep the stalk thick and sturdy as it grows?

A: Dieffenbachias are one of those trees from tropical rain forests which are easy to grow as a house plant. Many originated in South America. The varieties commonly sold have big, gorgeous, variegated leaves, leaves so beautiful that they compare with exotic flowers.

Although they are flowering plants with blooms that resemble a jack in the pulpit, a calla lily, or a peace lily, almost never do dieffenbachias bloom indoors. House plant people who have never grown a dieffenbachia find its arrow-shaped leaves familiar from having seen the plants in many people's houses.

Usually a dieffenbachia is sold as a young plant, looking like a fountain of leaves originating from a center at ground level. And therein lies the problem. As the plant grows, the bottom leaves age and die; new leaves grow above; gradually a tree trunk develops, with a leaf cluster at its top. It can be a handsome small tree, or it can become a limp and leaning specimen, a Charlie Brown tree.

There are two different ways to deal with the problem. Since dieffenbachias root easily, it is possible to keep a plant looking like a juvenile tree for many years, with no noticeable trunk. Restart a dieffenbachia which is growing a trunk by air layering. Cut a notch in the bark or remove a bark strip, just below a node. Wrap the area with damp sphagnum moss, cover with plastic wrap, and seal tightly. New roots will grow to fill the moss. When the roots are visible through the plastic, cut the plant just below them and put it in a new pot. This keeps the plant large.

Or make tip cuttings to start a smaller plant. Or cut the bare stem into sections three to six inches long. Lay the sections on or in potting soil, and cover with a plastic bag. This method will produce baby plants which grow from each node on the cut stem. Or make heel cuttings of one leaf with an attached strip of stem at the base; these also start small plants. Or, easiest of all, cut the trunk at a height of six inches. Usually it will sprout several new stems.

On the other hand, if you have room to grow a big dieffenbachia and long for an indoor tree, keep the plant in its original form. Move it to the next larger size pot when its growth slows or when roots are so crowded that they bulge out of the pot. Do not be surprised if a newly repotted tree starts to grow several more stems. If your plant is one that matures at four feet, you can keep it for many years. If it is a variety that matures at ten feet, eventually there will be a meeting of leaves and ceiling.

To keep a tree sized dieffenbachia growing straight, turn it every time it leans toward a window. Possibly a weekly turn will suffice. If not, be prepared to turn the tree every day. To keep the trunk sturdy, do not overwater. Although dieffenbachias are rain forest plants, they will be healthiest if the soil surface dries before each time of watering. And because they are rain forest plants, they are accustomed to poor soil. A tropical climate leaches out soil nutrients quickly. Imitate the natural growing conditions by fertilizing with a very light touch. Too much fertilizer makes a weak trunk, causes too fast growth, and encourages insect pests.

Do you wonder why a common house plant does not have a common name and is always called by the botanical name of dieffenbachia? Actually, it does have another name which no longer is used. The plant was called "dumb cane." Its name meant that it struck people speechless, or dumb, if they so much as tasted its sap. There were warnings that it was poisonous. All that turned out to be overstatement. dieffenbachia sap contains calcium oxalate, which can cause temporary numbing of the mouth and the vocal cords. To avoid that fate, do not chew on your plant.

The name dieffenbachia honors a nineteenth century naturalist, Johann Dieffenbach, who was in charge of the Royal Palace Gardens in Vienna, Austria. It is not uncommon for botanical names to be reminders of just such public figures from the past.

Q: What do you think of heirloom seeds versus new seed varieties?

A: Since both old and new varieties of seed have their merits, it is not surprising that both have partisan supporters. Personally, I see reason for both and grow both kinds in my gardens.

Those gardeners who strongly favor heirloom seeds talk about the necessity of preserving genetic diversity. Certainly it is true that if everyone grew the same variety of green bean, for example, within a few years there would be no green bean seed to grow. Diseases or insect pests would find weak spots and kill all the plants.

Having many varieties with different genetic heritages means that there always are survivors from any attack. On the other hand, a seed variety does not have to be old. Seeds are alive and thus always changing. New varieties develop naturally, not always because humans are fiddling with them.

Heirloom seeds also have disadvantages. An important one is that they were bred for a particular geographic location and may not be appropriate where growing conditions are different. Heirloom cucumbers developed east of the Mississippi were successful when they could resist attack by cucumber beetles, a major pest. Those beetles do not live here, so resistance does not matter here. Nor can heirloom watermelons bred in Missouri make ripe fruit in Montana's short summers.

Newer seed varieties may be either open pollinated, like surviving heirlooms, or hybrids. An advantage of hybrid seeds is that they mature at a more uniform time. An early hybrid tomato, for instance, can make many fruits in a short time, for a good crop even in a cool summer. A disadvantage is that hybrid seeds require hand labor and are therefore expensive. A dozen hybrid seeds may cost as much as a hundred open pollinated ones.

Finally, non-hybrid seeds, both old and new, are constantly changing. The heirloom seed planted this year will not grow into a plant identical to one with the same name from a century ago. I learned that when I planted green arrow peas, which were my favorite 30 years ago. I did not see those seeds for many years; when they reappeared, I planted them. To my surprise, they were not as productive or as flavorful as newer varieties I was growing.

The answer for me is to grow both old and newer seed varieties, and to experiment with a few seed varieties every year. I try to remember that the matter of which seeds are best is a complicated issue. Last year's favorite may not be the best one this year.

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