Saturday, April 19, 2014
By Tom Atwell
Invasive plants remain an issue in the gardening world, and they were a common topic among programs at the annual trade show of the Maine Landscape & Nursery Association last month in Augusta.
Autumn olive is already recognized as an invasive plant in Maine, along with Japanese knotweed and swallowwort.
Maine State Horticulturist Ann Gibbs reported that the state is about to hire a specialist in invasive plants. The position will be part of the Maine Natural Areas Program in the Department of Agriculture, Forestry and Conservation.
Gibbs said the state received 93 applications for the position, and that one of the new employee’s first duties will be to “develop a list of invasive plants” for Maine.
Maine now has a law banning the transportation of specific aquatic invasive plants, but it does not have a list of invasive land plants nor laws preventing their sale. Several other New England states do have such a list, and the University of Maine Cooperative Extension has a list of potentially invasive plants. Maine nurseries have stopped selling most of them,
The list includes Oriental bittersweet, Japanese barberry, Japanese knotweed, autumn olive, Oriental honeysuckle, burning bush, Norway maple and others.
Creation of a list of invasive plants probably will include debate on whether cultivars of some of these invasive species – which may or may not be invasive themselves – should be included on the list. It will be interesting to watch the process – and the result.
Rick Churchill, former chairman of the horticulture program at Southern Maine Community College and writer for the former People Places & Plants magazine, in another MELNA program discussed his firsthand experience battling invasive plants during creation of the first phase of the Arboretum at Fort Williams in Cape Elizabeth.
The site of the Cliffside Garden could have been a showcase for invasives, including knotweed, bittersweet, honeysuckle, Norway maple, swallowwort and more. He described how volunteers cut down and removed the invasive species. And when the plants resprouted, they cut them down again.
Once he had the invasive plants under control, he brought in native plants, including hayscented fern, that would keep the invasives out.
“People told me, ‘How can you plant that? It spreads everywhere,’ ” Churchill said. “Well, it does what we needed it to do” – cover the hill with ferns that were a bright green early in the season, changing to yellow and brown as the season progressed. Technically, because hayscented fern is a native plant, it can’t be labeled as invasive.
Other plants that he brought in were low-bush blueberries, bayberries and bearberries, all in sod form, although the blueberries brought a lot of weeds with them.
He reports some problems with the replanting. A white pine recommended by the landscape architect died the first year. Some pitch pines and jack pines that Churchill recommended looked dead, and he recommended that they be yanked. The architect recommended waiting, and the trees actually did produce more needles and looked OK later in the season.
A major problem was that there was just a little bit of horsetail equisetum in the soil that was brought into the site of the garden, and that is spreading rapidly. Horsetail is a weed that’s just about impossible to remove. So when you bring in soil, make sure it is horsetail-free.
Churchill’s talk was wide-ranging – the title was “What Plants Have Taught Me,” and he said he was added to the program at the last minute because the original program was all about marketing with no talks on plants.
One nugget on tree planting was new to me, and it made perfect sense. When Churchill first was in the business, guides said the hole for a plant should be 6 inches larger all around than the root ball. Now, he says, the guideline is to make the hole three times as wide as the root ball.
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