Regional Gardening Reports :: National Gardening Association

In the Garden:
Upper South
February, 2005
Regional Report

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Garden plants can become invasive pests when they produce an abundance of seeds, such as this butterfly bush 'Lochinch'.

Weeding Out Invasives

The indiscriminate and widespread use of certain non-native plants in our gardens, introduced without due diligence as to their growth habits, has culminated in a variety of environmental nightmares. Leap-frogging from the garden to the woodland, field, and roadside, a beloved ornamental plant can quickly become a costly nuisance, or, worse yet, a disaster.

The "black-and-white" solution to this problem is to ban the use of invasive ornamentals through legislation, and substitute a native plant in its stead in the garden. The dilemma with this method is that there exists the possibility, on occasion, of "throwing the baby out with the bath water." Just as these plants may have been accepted too quickly, so may they be banned in haste.

In a different world, where shades of gray are possible, another way of considering the problem with certain invasive plants is to first determine if the invasive nature applies to all the species and cultivars. This is a more cautious, slow-and-steady approach, but one not without merit and worth considering.

Selecting Varieties With Few Seeds
A perfect example of this was recently reported in the February, 2005, edition of The Avant Gardener newsletter (Horticultural Data Processors, Box 489, New York, NY 10028). Longwood Gardens, a large and venerable public garden in Kennett Square, Pennsylvania, has been testing numerous selections of two widely grown ornamentals that have come under fire as invasive pests: butterfly bush (Buddleia) and barberry (Berberis).

Although the seed dispersal of butterfly bushes (up to 40,000 seeds per flower head) can be prevented by deadheading, it seems improbable to assume that will always be done. (The prospect of a sheriff patrolling and arresting a gardener for not deadheading does hold a certain dark humor, however.)

What the researchers at Longwood determined was that out of thirty-five selections of Buddleia davidii, only two -- 'Orchid Beauty' and 'Summer Rose' -- produced very few seeds. Species that were found to be very low in viable seeds included B. fallowiana, B. hemsleyana, B. longifolia, B. nivea, and the new hybrids of the yellow-flowered B. weyeriana. In addition, Springmeadow Nursery, a wholesale supplier of young plants, describes the dwarf, white-flowered 'White Ball' as low in seed production.

The Japanese barberry (Berberis thunbergii) is popular for its adaptability and ease of growth, plus the range of foliage colors available. Unfortunately, barberries produce great quantities of seed that birds deposit in natural areas, creating dense, thorny thickets that overrun native plants.

In Longwood's tests of forty-one barberries, B. thunbergii 'Concorde', B. verruculosa, and B. wilsoniae ghutzunica produced no seeds at all. Very low in seed production were B. thunbergii 'Bonanza Gold', 'Golden Nugget', and 'Kobold'.

Both the philosophical and practical questions behind the approach of selecting for less-invasive species and cultivars may be too complex to consider as a viable option for controlling the crisis of invasive species. It's much easier to ban than thoughtfully control, yet it is an option that holds certain merit and should be considered.

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