Sometimes, a rose can harm a garden

No one would call Maine gardeners xenophobic. We welcome non-native plant species into our gardens, allow their escape from cultivation, and then, two or three generations of gardeners later, regard them as native. Consider the invasion of rugosa rose (Rosa rugosa), native to Japan, China, and Korea, and now ubiquitous along Maine’s coast.

Each July Fourth visit to the island village of Vinalhaven reveals further encroachment of rugosa rose into the surrounding native landscape. In the open fields bordering the rocky coastline, I see colonies of rugosa rose expanding, swallowing up space previously occupied by native plants such as northern bayberry, meadowsweet, sweet fern, and native roses. No doubt this invasion began when seeds from garden plants in the village were dispersed by birds.

Despite its beauty, rugosa rose should be viewed as a serious threat to the integrity of coastal Maine plant communities. The diverse native plant community on Vinalhaven, for example, seems destined to become a monoculture of the invader.

I have heard the argument that the invasion is over, that every section of Maine’s coast capable of supporting a monoculture of rugosa rose has been transformed by the invader, an argument offered by the environmentally unconscious as justification for the continued planting of the non-native rose in our gardens. What more harm can be done? There are still areas of Maine that can be protected and other areas that can be reclaimed, but only if we stop growing rugosa rose in our gardens.

There are alternatives. Chief among them are two very similar native rose species, R. carolina and R. virginiana. No, they are not as fragrant as rugosa rose, nor as long-flowering, and they have simpler flowers, a single row of pink petals surrounding bright yellow stamens. But their autumn display of burgundy-red foliage and deep red hips more than compensate.

So intense is our love affair with rugosa rose that finding a local source of native roses (and many other native plants) can be difficult. Many garden centers tend to follow rather than create demand for garden-worthy plants. At the same time, I have found some nurseries willing to go the extra mile for a customer interested in specific plants. So don’t give up! If one garden center tells you that they cannot get native roses (and then try to sell you a rugosa rose instead), take your business elsewhere!

Blooming Christmas Cacti

Last week I received a gardening question from Evangeline Cunningham of Bangor, asking how to coax a Christmas cactus into bloom. Her story is a familiar one, a Christmas gift that has grown into a “huge, beautiful green plant that never blooms.”

Well, as luck would have it, I ran into Elisabeth Curran, veteran Master Gardener and experienced horticulturist, at a recent Hancock County Master Gardener plant sale. Together we developed the following strategy for the re-blooming of Evangeline’s plant.

First, let your Christmas cactus spend the summer outside in partial shade (full sun burns the leaves), watering only when the soil is dry and fertilizing sparingly, perhaps at half the recommended rate. Then, in early September, slowly adjust the plant to life indoors by gradually increasing the number of hours it spends indoors each day.

To form flower buds, Christmas cacti need a long, uninterrupted dark period each day. Beginning in mid-October, put your plant in a dark closet for twelve continuous hours each day. Continue this dark treatment until you see flower buds forming.

Good luck!