January/February 2000 issue

Gardeners Information Service

I’ve noticed that the ‘Marguerite’ and ‘Blackie’ cultivars of sweet potato vines are readily available in the trade. Are the swollen underground roots of these cultivars edible like a “normal” sweet potato? Can you propagate the sweet potato from these roots? —C.H., Bountiful, Utah

Unlike their agricultural counterparts, Ipomoea batatas ‘Marguerite’ and ‘Blackie’ are bred for ornamental properties rather than edible roots. ‘Marguerite’ is grown for its broad, heart-shaped, chartreuse foliage on trailing vines, and ‘Blackie’ is becoming a favorite in the garden for its dark purple, deeply lobed foliage that makes a great companion for plants with brightly colored flowers or foliage.

According to Janet Bohac at the USDA’s Vegetable Laboratory in Charleston, South Carolina, ‘Marguerite’ seldom produces a “usable” edible root and ‘Blackie’ almost never does. If, by chance, such a root is produced, there is no reason it could not be eaten.

Bohac adds that while it is possible to propagate these varieties from slips produced by their roots, propagation from cuttings is much easier.

Do you have any literature on Japanese yews? We have some planted around our home near Milwaukee and can’t seem to keep them alive. Six were planted, two already dead, two more in the process of dying and the last two (most recently planted) doing so-so. —D.M., waukesha, Wisconsin

The most common problem associated with growing Japanese yew (Taxus cuspidata) is its intolerance of poorly drained soils. In fact, anything less than excellent drainage can result in an unthrifty plant or even death.

Typical symptoms of poor soil conditions on a Japanese yew begin with plants yellowing from their tips. If the condition is severe, the entire plant becomes chlorotic or yellow, wilts, and eventually dies.

If you suspect from the above description that poorly drained soil is your problem, move the two surviving plants to a site with better soil conditions. Brent McCown, professor of horticulture at the University of Wisconsin, suggests replanting in an 8-to-12-inch-high raised bed filled with a mixture of silt loam soil and organic matter such as peat or compost. Mulch in summer to moderate moisture stress.

Another solution is to replant with shrubs that tolerate poorly drained soils better than yews. “For conifers that can be used like yew,” says McCown, “probably the best choice for wet areas is American arborvitae (T. occidentalis).

Other shrubs that tolerate poorly drained soil include: chokeberry (Aronia spp.), summersweet (Clethra alnifolia), inkberry (Ilex glabra), or red-osier dogwood (Cornus sericea). All are hardy in your region, but only inkberry is evergreen.

I recently purchased a plant labeled Alsophila australis, but it doesn’t look much at all like the pictures of this plant in my American Horticultural Society reference book. It looks much more like Cyathea dealbata or Dicksonia antarctica, but not exactly like either of those, either. Can you recommend a good reference book on tree ferns? I would like to learn more about them, as well as see if I can determine the species I have. —A.D., Houston, texas

Some plants of the Alsophila and Cyathea genera—both in Cyatheaceae, the tree fern family—are listed as one genus by some authorities and vice-versa by others. According to the American Horticultural Society’s A-Z Encyclopedia of Garden Plants, Alsophila australis, commonly known as rough tree fern, is a synonym for Cyathea australis. Plants labeled as C. cooperi are also considered synonymous with C. australis.

To further confuse matters, some plants in the Cyathea genus are sometimes also listed in the Sphaeropteris and Nephelea genera.

Tree fern is the name commonly used to refer to members of Cyatheaceae that have an erect, stout rhizome that forms a trunk, or caudex, with a crown of leaves at its apex. While this growth is also developed in plant families such as Blechnaceae, it is only in Cyatheaceae that the plants reach significant size and ecological importance.

We are not aware of any books devoted solely to tree ferns, but the following general publications might prove helpful:

• Ferns to Know and Grow by F. Gordon Foster. Timber Press, Portland, Oregon, 1993.
• Ferns for American Gardens by John T. Mickel. Macmillan Publishing Company, New York, 1996.
• Encyclopaedia of Ferns by David L. Jones. Timber Press, Portland, Oregon, 1992. m

William May, Gardeners Information Service, and Marianne Polito, Gardeners Information Service Manager