Q&A WITH BOB POLOMSKI Extension Consumer Horticulturist Clemson University

I recently received a large dieffenbachia from a friend. It appears healthy and I have it near an east-facing window, but I'm concerned about the moisture droplets that form on each leaf and sometimes drip off. Is this normal?

B.M., Wichita Falls, TX

Answer: Your “weeping” dieffenbachia is exhibiting a phenomenon called guttation (from the Latin gutta, which means drop). This condition usually occurs in the early morning when the soil is moist and transpiration, or water loss from the leaves, is low. As water is absorbed by the roots, it is pumped into the xylem, or water-conducting tissues. But instead of evaporating through the leaves' stomata (pores), root pressure forces water out off the leaf margins and leaf tips through specialized pores called hydathodes.

The phenomenon is perfectly normal, but you can reduce its incidence by only watering your dieffenbachia when the top inch of potting mix feels dry.

I have collected the seed of a wild lotus and I want to know how to germinate it.

F.T., by e-mail

Answer: American lotus (Nelumbo lutea), often known as water chinquapin, is native to the eastern and central United States. This aquatic plant is closely related to water lilies. It produces large round floating leaves joined to a thick rhizome by stalks. As new growth emerges over the course of a season, aerial leaves shaped like shallow bowls are produced on stems that rise five feet or more above the water. Its flowers, which appear on even longer stalks, may be white, pale yellow, pink, or deep rose and range from four to twelve inches across. In the center of each flower is a yellow receptacle with tiny holes; it looks much like a shower head. This seed pod enlarges as it matures, changing to green and then to brown. By that point the individual seeds are loosely held in depressions on the pod's face. Because of their decorative value, these seed pods are often dried, sometimes bronzed or silvered, and used in floral arrangements.

To germinate your seed, first scarify or abrade the impervious seed coat with sandpaper or a file. Then sow the seed in a mix of two parts heavy garden soil and one part coarse sand in a nondraining container. Plant the seed at a depth twice its diameter and fill the container with water so that the mix is submerged by two inches. Set the container in a south-facing window where the air temperature is above 75°F. Keep the water temperature above 65°F. The seed should germinate in two to three weeks.

When three leaves have appeared, the seedlings can be transplanted to larger pots filled with heavy garden soil. These pots can then be set in a larger container of water. Be sure that there is enough water to support the developing leaf pads.

When water temperatures outside have reached at least 70°F, young lotuses can be moved outdoors. Each plant should then be transplanted to a container at least 9 or 10 inches deep and 16 to 20 inches in diameter. Use half a pound of commercial aquatic plant fertilizer per bushel of soil. Cap the soil with a layer of pea gravel before submerging the container. Position the pots that the gravel is three to four inches below the water's surface.

I'm concerned about a large black walnut tree growing in the backyard of the home we have recently purchased. Despite its age and beauty, I wonder if I should remove it, in order to grow other plants. Are there any plants that are immune to the toxin produced by the black walnut?

H.L., Danville, VT

Answer: The inhibitory effect of the native American black walnut (Juglnns nigra) on certain plants is well documented. Indeed, black walnut is the oldest known example of allelopathy, whereby one plant produces chemicals that interfere with the growth and survival of other plants. In the case of black walnut, allelopathy begins with a colorless, water-soluble, nontoxic compound called hydrojuglone. The highest concentrations occur in the buds, nut hulls, and roots. Upon exposure to air, hydrojuglone gets oxidized to juglone, a highly toxic compound that inhibits plant growth and nutrient uptake. Juglone exudes from roots and leaches from leaves, branches, and fallen leaves and nuts. But because it is not very soluble in water, it is not very mobile in the soil.

Susceptibility to juglone is species dependent. Solanaceotis plants in particular are highly susceptible. Tomatoes are the canaries in the coal mine, developing “walnut wilt,” which is characterized by wilted, yellow leaves and eventual death. Cutting the stem longitudinally will reveal brown discolored tissues.

Many herbaceous and woody plants, however, can coexist with black walnut, as noted by Frank Robinson in his Horticulture article “Under the Black Walnut Tree” (October 1986), Robinson found that the great majority of cultivated plants he tried growing beneath two black walnut trees in his Rochester, New York, garden did fine. His list of tolerant plants includes bugleweed (Ajuga reptans), cranesbill (Geranium sanguineum), summer phlox (Phlox paniculata), lamb's ear (Stachys byzantina), weeping forsythia (Forsythia suspensa), rose-of-Sharon (Hibiscus syriacus), Canadian hemlock (Tsuga canadensis), and Japanese maple (Acer palmatum). Interestingly, Robinson found differences in susceptibility among cultivars. For example, small-flowered cultivars of daffodils flourished, while trumpet and large-flowered flat-cupped daffodils succumbed to the toxin.

Several lists of black walnut-tolerant plants can also be found on the Internet. See “Trees for Problem Landscape Sites—The Walnut Tree: Allelopathic Effects and Tolerant Plants” (www.ext.vt.edu/pubs/nursery/430-021/430-021.pdf) and “Black Walnut Toxicity” (www.hort.purdue.edu/ext/HO-193.pdf).

Besides proper plant selection, you can minimize the accumulation of juglone in the root zone of your black walnut by raking up fallen leaves, nuts, and other debris. If possible, incorporate organic matter into the surrounding area to encourage microbial growth, which in turn will speed the breakdown of the walnut's toxins.

For the past several winters I have been battling Florida betony. It is infesting my St. Augustine grass lawn and has invaded my flower beds. Is there anything, besides hand pulling, that I can do to stop its spread?

P.T., Cairo, CA

Answer: Florida betony, or Florida hedgenettle, is an aggressive cool-season perennial weed in the mint family (Lamiaceae) that occurs throughout the Southeast from Florida north to Virginia and west to Tennessee, Arkansas, and Texas. It has opposite triangular toothed leaves and square stems and can reach a height of two feet. In April and May it produces whorls of white to pink trumpet-shaped flowers in its leaf axils.

Florida betony is a formidable foe because of its network of underground stems, or rhizomes, which bear white tubers at their tips. These segmented tubers resemble the tail end of a rattlesnake, hence its other common name, rattlesnake weed. The tubers are typically one to four inches long and about a half inch in diameter, but they can grow to more than eight inches in length. Florida betony reproduces primarily by these tubers, which can be found as deep as 12 inches down, and it also produces seeds. In the fall seeds and tubers sprout and begin active growth. Growth slows during midwinter's cold but then resumes its vigor until late spring. After flowering, Florida betony goes dormant with the onset of hot temperatures and humidity.

Florida betony can be found in full sun to part shade and from dry to wet soils. It usually invades thin or bare lawn areas. Isolated plants can be hand pulled, but take care to remove the rhizomes and tubers. You can also spot-treat Florida betony with a post-emergence herbicide containing 2,4-D + MCPP + dicamba (Trimec, Weed-B-Gon). Apply in October and, if necessary, make a second application in late February when the Florida betony is actively growing.

In landscape beds, a two- to four-inch layer of mulch atop several sheets of newspaper or landscape fabric will hinder its emergence. You can also use a preemergence herbicide containing dichlobenil (Casoron). Dichlobenil, however, will kill or severely injure herbaceous ornamentals and newly planted woody ornamentals. Apply between December and February around established ornamentals when the soil temperature is below 55° F. Do not use dichlobenil on sandy soils, where it may lead to groundwater contamination. Glyphosate (Roundup) is an effective nonselective herbicide, particularly when applied to the Florida betony when it is in bloom.

When our local flower show ended, I picked up a flowering crab, some spireas, and a rhododendron very cheaply. They have leaves and flowers, way ahead of the plants outside. I'd like to try to plant them outdoors, but, if I do, won't they just freeze?

E.D., Manchester, MI

Answer: Yes, plants that have been coerced into premature growth are likely to die if they are immediately planted outdoors. They've gone from being fully cold acclimated to being susceptible to freezing temperatures. Unfortunately, there is no easy way to return these plants to their previously dormant (and cold-tolerant) state. The best that you can do is to store them in a cool, well-lit location where the temperature will remain above freezing. A closed-in (but unheated) porch would suffice. Be sure to keep the root balls and the soil in the containers moist.

When you are safely past the last frost date in your area, you can move them out into your landscape. But by then you will understand why such plants are offered at bargain prices when flower shows close.