Counting Callerys

By Joan Butler

During the past year, I decided to make use of my “down time” by taking advantage of lectures on gardening and horticulture that were offered via Zoom. Thank goodness for Zoom! I also decided that this would be the perfect time to continue my studies in the National Garden Club’s Environmental School program. The State Garden Club of Missouri was offering Course 2 remotely in March at a time that worked for me, so I signed up. It was a great course, and it was especially relevant because, although many of the environmental issues affecting Missouri are different than the issues that affect us here in New England, I found that many of them are exactly the same.

Malissa Briggler, the head botanist of the Missouri Department of Conservation, was the instructor for the class on “Endangered Plant Species of Missouri”. She also talked about plants that are on the Missouri invasive plant list and their impact on native plants. According to the World Wildlife Fund, Massachusetts is in the “temperate broadleaf and mixed forests” biome, and Missouri is in the “temperate grasslands, savannas and shrublands” biome. Two very different environments, but the overlap of invasive plants on the list for both states was sobering: Japanese knotweed, burning bush, Autumn olive, purple loosestrife, Oriental bittersweet, garlic mustard, mutiflora roses – and the list goes on and on. At first, it was discouraging to realize that the thugs we battle here in Massachusetts are so widespread beyond our state that it is obvious they are here to stay. But it also underscored the fact that environmental issues are not just local issues, they are national/global issues that involve us all. 

Bradford Pear saplings on the side of the road

One of the plants on the Missouri invasive list is Bradford or Callery pear. This was discussed at length because of its impact in displacing native plants and overtaking open fields. This reminded me that Doug Tallamy (author of Bringing Nature Home) spoke about the invasive tendencies of Bradford pear at a program I attended a few years ago. And recently, Uli Lorimer, of the Native Plant Trust, said that Bradford pear was a plant that was being watched.

Callery pear is native to Asia. It was brought to the US in the early 1900s because of its resistance to fire blight. Hybridizing efforts ultimately produced a cultivar with an upright rounded shape, white flowers, no thorns and red fall foliage. It was named ‘Bradford’ and was introduced by the US Department of Agriculture as an ornamental landscape tree in the 1960s. Bradford pears are considered self-incompatible, which means they cannot be self-pollinated, nor can they be cross-pollinated by another tree of the same cultivar because they are all genetically the same. But, in time, other cultivars were introduced commercially (eg. ‘Chanticleer’, ‘Aristocrat’, ‘Autumn Blaze) which led to opportunities for cross-pollination and abundant fruit formation. Birds and other animals eat the fruit and spread the seed far and wide.

As is typical of apple or other pear trees, the seeds produced by Callery pear cultivars do not come true to type. They are often more like the original wild types, and many now bear thorns just like the wild types. They grow densely along roadsides, fields, disturbed areas at the edge of woodlands and in open woods. Although pollinators may be attracted to the flowers, our native insects do not feed on the leaves, which means that Callery pears are a “food desert’ for many songbirds that rely on insects for food. Additionally, they leaf out before many of our native trees do and hold onto their leaves longer in the fall.

Bradford pears are nearing the end of their bloom cycle here in Metrowest Boston. They are very identifiable because of their early bloom time, profusion of white flowers and upright rounded shape. Because I had learned more about them so recently, I became very aware of just how prevalent they are here. They are street trees, neighborhood trees, lawn trees, park trees – they are everywhere! I noticed some areas where they had shown up along roads, and one area with a dozen or so along the edge of a vacant lot. I’ll be on the watch for fruit later in the season. 

In Missouri , in celebration of Arbor Day, homeowners have been offered a free sapling of a native tree if they show pictorial proof that they have cut down a Callery pear cultivar on their property. Clemson University Extension in South Carolina has offered a similar “buy back” program. It’s hard to predict if it will come to that here in Massachusetts, but in light of the fact that so many of the plants that are on our Invasive Plant List are also on the Invasive Plant Lists of other states, it is certainly something of which we should be aware.

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Gardening in the Hellstrip

The hellstrip — the space between a street and a public sidewalk, also known as a tree park, boulevard, meridian, and planting strip — is getting a lot of attention these days with the publication of Evelyn Hadden’s Hellstrip Gardening by Timber Press. This comprehensive guide with gorgeous color photographs of hellstrip gardens across the country offers inspiration and visual guidance to anyone ready to tackle this final frontier.

Hellstrip gardening is nothing new to my friend Kathy, who has been adding curb appeal to her home with hellstrip plantings for 15 years. Kathy began her roadside garden when she got tired of trying to keep the lawn grass alive in the hellstrip year after year. Always keen on water conservation, Kathy wanted a low maintenance solution for this long, sunny expanse. Her large backyard garden had also become shaded over the years as the pine trees grew taller and taller, so the sunny hellstrip offered a chance to relocate her sun lovers from the backyard and to try some new plants in this totally different environment.

She began the garden by digging up a small section of sod around her mailbox, amending the soil, and planting various sedums that would be low maintenance and drought resistant. Bit by bit, the hellstrip garden grew, and then expanded to the other side of the driveway. Now it measures close to 100 feet, and boasts a wide variety of perennials. Kathy learned through trial and error which plants to grow, and which plants to avoid. Some perennials, like yarrows, were too tall and floppy. Annuals were too labor intensive, except for the portulaca that self sows and returns year after year. But there were many perennials that acclimated to this dry, sunny area with its relatively poor soil.

Mediterranean plants and herbs – many of which sport silver foliage and prefer a sunny situation with lean soil and good drainage, thrive in Kathy’s roadside garden. Sedums, Lamb’s ears, salvia, sage, alliums, fescues, rosemary, thyme, mint, sea lavender, and catmint bask in the baking hot sun. The garden delights passersby with a changing palette of blooms and foliage. In the early spring, crocus, creeping phlox and species tulips, which love the good drainage, cheer up the border with their blooms. They are followed by stately bearded irises, columbines and poppies in June, and daylilies, helianthus and coreopsis in mid summer. A prickly pear cactus at the base of the mailbox surprises visitors with its yellow flowers in July. Sedums steal the show in August. In a shadier part of the garden, hostas and heucheras provided beautiful foliage from spring to fall.

Gardening in the hellstrip has its challenges. The soil in these areas is usually cheap, compacted fill. Kathy amends it at planting time with compost, and has been top dressing with leaf mulch. Because of the distance from the house, the garden is difficult to water. Although Kathy does not irrigate regularly, newly installed plants need supplemental watering, which amounts to many trips with a watering can. Weeds easily blow into the garden and crabgrass is a particular problem. Since the hellstrip is town-owned property, large sections have been dug up utility companies several times without prior notice.

But overall, gardening in the hellstrip has been a positive experience for Kathy. Neighbors stop by to admire the garden, and Kathy receives many compliments on sprucing up the neighborhood. “The hellstrip builds community,” says Kathy. “People stop by to chat and ask about the flowers. And it gives me a chance to try plants that I couldn’t grow anywhere else in my garden.”

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Invasive Vine “Swallows Up” Your Garden

I came home from a week’s vacation to find that my garden had virtually “exploded” while I was gone. The heavy rains of June followed by the July heat wave turned my garden into a lush jungle of towering lilies, heliopsis, and hydrangeas. The explosion of flowers was coupled with an explosion of weeds, including the invasive black swallow-wort vine that I battle every year.

Also known as Louis’ swallow-wort, Cynanchum nigrum is a member of the milkweed family imported to the U.S. from its native Europe as an ornamental vine. It was first noted in Ipswich, MA in 1864, “escaping from the botanic garden where it is a weed and promising to become naturalized.” Since then, black swallow-wort has become an invasive nuisance in the Northeast and Midwest, crowding out native plants in fields and forests. It is also a deadly host for the monarch butterfly, which lays its eggs on the vine, but its larvae do not survive feeding on this plant. Conservancy groups throughout the country are trying to educate the public about the threat of this plant to the environment.

The vines emerge in the spring, and can literally grow a foot overnight in wet weather. They quickly wind around your precious peonies, pulling the heavy blooms down to the ground, sprawl over entire shrubs, or grow right through the center of a rare epimedium that you bought from a hybridizer for a tidy sum. These vines thrive everywhere, from sun or shade, rich humus or heavy clay, alkaline or acidic soil.

Black swallow-wort sports glossy oval-shaped leaves with pointed tips, 3-4 inches long, that occur in pairs along the stem.

The small, dark purple flowers are star-shaped and borne in clusters.

The flowers are self-pollinating and quickly produce a bounty of seed pods that dangle from the stems. The seeds are equipped with their own downy parachutes that aid in wind dispersal, which begins in late July and continues through fall. The plants also spread through underground rhizomes that form large clumps.

So how do we control this thug in the garden? As with all invasive species, early detection and removal is the best approach. There are no biological controls for black swallow-wort available in the U.S. Mowing will not eradicate the plants, but will at least prevent them from forming seeds. Once seeds have formed, the plants should be carefully cut down and bagged so that the seeds don’t disperse. The vines can also be dug out, but care must be taken to remove the complete root crown, which is difficult to do. Even a tiny piece of white root left behind will soon sprout into a new plant. Dug plants should be burned or bagged and disposed of in the trash.

Although I dislike using herbicides in the garden, chemical control is recommended as the most effective means for large, established infestations. Glyphosate (Roundup) is effective if sprayed on when the plants are in flower (prior to that, the plants do not have enough leaf surface area to deliver a killing dose to the roots.) If the black swallow-wort is twining around desirable plants, the glyphosate can be applied with a sponge or brush. Another alternative to spraying is to cut and dispose of the stems and apply a 100% solution of the herbicide concentrate directly to the cut stem surfaces with a small brush.

Unfortunately, once black swallow-wort appears in your garden, you will be battling it for several years. So don’t wait – if you see even the tiniest sprout of this tenacious vine, pull it immediately! Or you may return from vacation later this summer to find your favorite plants “swallowed up” by this insidious creeper!

Photos courtesy of Marie Brown