By Barb Delisio
OSU Ext. master gardener volunteer
Many of us know about native plants, but do you know the difference between non-native and invasive? Non-native plants originate in other parts of the continent or world. They lack the natural predators and disease that control them in their natural habitat.
Ohio has about 700 kinds of non-native plants, but only about 100 are considered invasive, meaning they move into an area and multiply quickly, crowding out native ones. This is especially true in wetlands and wooded areas.
Many plants considered invasive are still sold at garden centers. Plants brought in to enhance our landscapes have caused much of the problems we are seeing today. How often during the summer months have you seen acres of tall, purple blooms along the road sides? This plant — purple loosestrife — is quite beautiful, especially in mass, but it multiplies quickly. It can have 1-50 square stems, which produce the purple flowers, per plant. When the plant sets seed, which all flowering plants do, it can exceed 100,000 seeds in a season.
The new plants, because of their deep taproot and multiple rhizomes, form a thick mat that crowds out other plants in the area. We strongly discourage you from planting purple loosestrife in your garden, but if you feel you must, at least cut off the flower heads before they set seeds.
A more common, popular plant we consider invasive is English Ivy. We love the way it fills in all those areas of shade in our gardens, but its evergreen leaves smother other native plants by denying them light. It reaches maturity and sets seeds only when It grows vertically. So, if you must have it in your garden, keep it growing horizontally and it won’t go to seed and take over your yard.
Another plant becoming more invasive due to the popularity of butterfly gardens is some cultivars of the butterfly bush, Buddleia. The native plant that supports butterflies is the butterfly weed (Asclepias tuberosa), a 12- to 36-inch plant that doesn’t spread, compared to the very large Buddleia, a shrub that takes over everything around it.
The most invasive plant species in our Ohio wetlands and wooded areas are Japanese honeysuckle, Japanese knotweed, autumn olive, buckthorns, purple loosestrife, garlic mustard, multiflora rose and bush honeysuckle. Besides ivy and butterfly bush, other home garden plants to watch are periwinkle and burning bush. Oakleaf hydrangea (Hydrangea quercifolia) is a great substitute for burning bush. It is red in fall, but with the addition of wonderful blooms through the summer. For more, see http://go.osu.edu/invasives2 and http://go.osu.edu/invasives.