A sense of herbs - Invaders at the garden gate

September 05, 2004|by Dorry Baird Norris

Details about how and when people began carrying plants from one place to another are skimpy. It certainly started well before the reign of Queen Hatshepsut of Egypt (circa 1518 B.C.) who, it is recorded, sent an expedition to Punt to collect valuable cinnamon and myrrh trees.

During the Dark Ages, plants moved from one place to another carried by monks (perhaps in the drawstring purses attached to their rope belts.) The monks sought new medicinal plants for their physic gardens. Poppy seeds transported by the knights returning from the Crusades were planted and the poppy juice proved a welcome painkiller.

In the 16th century came the golden age of exploration. Exotic plants like peppers, potatoes, cocoa and tomatoes made their way to Europe. Early on, they were considered curiosities.

During the 17th century, with the development of masonry orangeries, in which temperature could be controlled, gardeners were able to grow all manner of exotic plants. By Queen Victoria's time huge glass houses became fashionable for those seeking to collect the rare and unusual. During this golden age of plant exploration botanists ranged the globe in search of the next unusual treasure. Even the northeastern United States was pulled into the search. Philadelphian John Bartram began to catalog the plants he found in his travels through the country.


We are now learning that the introduction of foreign plants into new locations can have its drawbacks. Plants, kept in check by limited soil, rain, hungry bugs or animals in their native habitat may run rampant elsewhere without those controls. One only has to mention "kudzu" to any Southerner to elicit a groan of horror. This vine, brought to the United States as an ornamental, arrived without the insect predators that kept it under control in its native Japan. Now, it smothers the Southern landscape.

Troublesome plants in areas foreign to them are labeled invasives. Non-native plants that are invasive grow rapidly and displace native plants in natural areas.

Some of these intruders have long been available for the home landscape in local nurseries. Many of these plants spread rapidly and upset the complicated balance between native plants and wildlife. The pollen from these intruders may also alter the genetic makeup of native plants.

Soil and climate help or hinder these plants from spreading, so the plants defined as invasive vary from region to region.

In the Middle Atlantic states, the following plants have been identified as "plant invaders" of natural areas. For instance, the Norway maple, even though it is beautiful, can displace our native sugar maple.

Herbaceous Plants

Garlic mustard (Alliaria petiolata)

Japanese knotweed (Polygonum cuspidatum)

Purple loosestrife (Lythrum salicaria)

Lesser celandine (Ranunculus ficaria)

Canada thistle (Cirsium arvense)

Chinese lespedeza (Lespedeza cuneata)

Chinese silver grass (Miscanthus sinensis)

Common day lily (Hemerocallis fulva)

Common reed (Phragmites australis)

Giant reed, wild cane (Arundo donax)


Autumn olive (Elaeagnus umbellata)

Bush honeysuckles, exotic (Lonicera species)

Japanese barberry (Berberis thunbergii)

Multiflora rose (Rosa multiflora)

Privets (Ligustrum species)

Wineberry (Rubus phoenicolasius)

Winged burning bush (Euonymus alata)

Butterfly bush (Buddleja species)

Japanese spiraea, Japanese meadowsweet (Spiraea japonica)

Jetbead (Rhodotypos scandens)


Bradford pear (Pyrus calleryana 'Bradford')

Norway maple (Acer platanoides)

Princess tree (Paulownia tomentosa)

Tree of Heaven (Ailanthus altissima)

Silk tree, mimosa tree (Albizia julibrissin)

Paper mulberry (Broussonetia papyrifera)

Sawtooth oak (Quercus acutissima)

White mulberry (Morus alba)


English ivy (Hedera helix)

Kudzu (Pueraria montana v. lobata)

Oriental bittersweet (Celastrus orbiculatus)

Porcelainberry (Ampelopsis brevipedunculata)

Wisterias, exotic (Wisteria sinensis, W. floribunda)

Creeping euonymus (Euonymus fortunei)

Five-leaved akebia (Akebia quinata)

Japanese honeysuckle (Lonicera japonica)

Periwinkle (Vinca minor)

This is a long list but it gives you a benchmark from which to start reducing the threat from these plants.

To help stop invasives in their tracks:

· Don't disturb natural areas.

· Don't dump yard waste in or near natural areas - it may contain seeds of invasive plants.

· When you shop for garden plants skip the invasive exotic species.

· Remove invasive plants entirely or manage them to prevent spreading (such as cutting off flower heads or seeds). We are already doing that with our butterfly bushes.

· Offer to assist in exotic plant removal projects from public property.

· And most important of all, don't add these plants to your landscape.

For information on eradicating these plants go on the Web to and type in "exotic plant eradication Maryland" or write Maryland Native Plant Society P.O. Box 4877; Silver Spring, MD 20914.

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