Is Bittersweet Invasive? | Gardening Advice
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Last spring I sent away for three bittersweet plants and received one male and two female plants. These grew high with great leaves, but no berries. What went wrong? — D.C., Pascoag, RI
First of all, as pretty as their berries are, Oriental bittersweet (Celastrus orbiculatus) is widely considered one of the most threatening invasive plants in New England. Like the kudzu vines that dominate southeastern natural areas, this is the vine we see throughout this region, choking out large trees and causing major damage to natural areas. This species should not be grown in your landscape. Your most responsible action would be to remove your plants before they produce berries, which birds can spread into nearby woods. This is one situation when plastic replications of the plant are preferred to the authentic.
To answer your basic question, “di-oecious” plants, whose male and female flowers occur on separate plants, need to become mature before their female flowers set berries. Hollies (Ilex), bayberry (Myrica), and ginkgo are other examples of plants whose sexes are separate. If you want berries, it is wise to purchase cultivars already identified as female, and often a male pollinator is needed. Should you buy seedlings, you won’t know whether you have one that produces berries until it is old enough to flower. Also, when lush growth occurs in high-fertility conditions, many plants will tend to produce leafy growth and fewer flowers and berries. A measure of neglect often encourages better flowering and berry production.
R. Wayne Mezitt is the chairman of Weston Nurseries in Hopkinton, Massachusetts.