Note: this article was originally published in 1991. Research since then has changed the outlook for purple loosetrife. See an updated article on this subject.
The definition of a weed is a plant out of place. To some, perennials like globe thistle and goldenrod are desirable garden plants. Others object to these plants and consider them weeds. There are no right or wrong answers when dealing with such plants and the decision to cultivate or eradicate is simply a matter of personal preference. However, when a cultivated plant escapes its garden setting and threatens to disrupt a fragile ecosystem, certain precautions must be taken.
One plant that has posed a problem for wetland areas is purple loosestrife (Lythrum salicaria). Purple loosestrife is a tall, bushy, long-lived perennial. Plants produce erect stems which become covered with pink, magenta, reddish purple, or deep purple flowers in June and July. Because of these beautiful flowers, the ease with which the plant is grown, and lack of serious pests, purple loosestrife has gained widespread popularity. However, the species may freely reseed in wet areas, choking out large areas of native vegetation in marshland areas or around lakes and streams, thus ruining habitat for waterfowl. Because of its invasive nature, purple loosestrife (Lythrum salicaria) has been designated as a secondary noxious weed in Iowa. No person shall sell, offer for sale, or distribute purple loosestrife in this state.
There are, however, several cultivated varieties of purple loosestrife (Lythrum virgatum and hybrids) that can be grown by home gardeners (but see updated article ). These varieties are considered sterile or nonaggressive. Home gardeners can plant the following seven varieties in "ornamental gardens" only.
Dropmore Purple -- 3 to 4 feet tall with deep purple flowers.
Morden Gleam -- 3 to 4 feet tall with rosy pink flowers.
Morden Pink -- pure pink flowers.
Morden Rose -- 3 feet tall with rose-red flowers.
Rose Queen -- purplish-pink flowers.
Gooseneck loosestrife (Lysimachia clethroides) is sometimes confused with purple loosestrife. Gooseneck loosestrife, however, is another plant species. It does not present a threat to wetlands and can be freely planted in Iowa.
This article originally appeared in the June 19, 1991 issue, pp. 109-110.