Old favorites

You could recreate the front yard plantings in my neighborhood with a palette of fewer than ten shrubs. 

Big yews are common in local yards

For foundation plantings, there are the yews, the pieris and mountain laurels, and those gigantic Catawba rhododendrons. Then perhaps there’s a forsythia, a juniper, a burning bush, a barberry, or a spirea in a sunny patch closer to the street.

A nearby rhododendron ready to flower next spring

    How did we bond with these old favorites?  I ran across a strenuous bit of scholarship that helps answer this question. Denise Wiles Adams, a garden historian, spent almost 10 years reading through American nursery catalogs published from 1719 to 1940 to tally the plants offered and how widely they were sold. She presents some of her results in Restoring American Gardens, An Encyclopedia of Heirloom Ornamental Plants 1640-1940. 

    From her book I learned that those Catawba rhododendrons that are so prevalent in my neighborhood have been around the Boston area since at least 1841. Rhododendron catawbiense is a native of the southeastern US that grows to the size of a truck in the right shady conditions. 

Catawba rhododendron, dense and reliably evergreen, flowering in late spring

Michael Dirr, in his invaluable Manual of Woody Landscape Plants, describes it this way: “Very handsome and aesthetic broadleaf evergreen; the flowers are beautiful but the foliage is equally valuable; beautiful when used in mass; hardy to about -20ºF with proper cultivar selection.” 

     Evidently a whole lot of nurseries, garden centers, and consumers agree, because there’s hardly a yard in my neighborhood that doesn’t contain at least one of these shrubs. 

This one was growing in our yard when we arrived

I still remember seeing these rhododendrons in the wild in Great Smoky Mountains National Park 40 years ago. It was like seeing lions on their home savannah.

    Forsythia is another landscape cliché in my region. The one we see is Forsythia x intermedia, a hybrid between two Asian species. 

At the corner of our lot. With more sun it would make more flowers.

Adams reports that one of its parents. Forsythia viridissima or golden bell, was introduced to the US in 1844. The genus was named after William Forsyth, a royal head gardener and a founder of Britain’s Royal Horticultural Society. 

     A less than prescient 1870 authority commented, “Its luxuriance, the earliness of it bright small yellow flowers, and the fact that it is a comparatively new thing, has given this shrub a reputation that it may not sustain.” The hybrid got here around 1880 after it was discovered in a German botanic garden. Can you drive a block in April without passing a glowing yellow forsythia bush?

Correctly pruned. Shearing forsythia is criminal--photo 4028mdk09

    Adams points out that we generally buy what’s readily available at garden centers—or now, at big box stores. That means that our choices are partly determined by what’s easy to propagate and grow on a large scale. Both forsythia and Catawba rhododendrons fit the bill.

To get to market, most trees and shrubs have to be easy to produce

    Adams observes that plant fashions come in cycles. When we think we’re planting something daring and original, we’re probably just rediscovering a plant that’s been out of vogue. Catawba rhododendrons and forsythia haven’t had a chance to disappear, though, because they pretty much live forever. Boring clichés or beautiful classics? You decide.

Nadia, my garden companion

Our dog Nadia died August 31. I miss her for so many reasons. For one, she was my gardening companion.

Nadia

    Nadia was a German shepherd mix who was 10 months old when she came into our lives in March 2002. At that awkward age, she was full of nervous energy, dashing around the house and trying to understand her new environment. She’d been sent back to the shelter by her first family, who said their children hadn’t kept a promise to take care of her.

    Nadia seemed to have had a good life before her four scary days back in the shelter. She liked humans and knew how to live with them. Our family of four went to Jamaica Plain to meet her and brought her home in our Subaru wagon. We imagined she’d stay in the far back while we sat in the seats. Instead, she leapt into the back seat and then the front to nuzzle us excitedly.

She liked to sit up front

 
    Once we got home, she explored the backyard. She loved to play tag but couldn’t see the point of retrieving anything. She buried bones in the compost piles. She designated a digging spot next to the side porch, where she excavated a hole three feet deep. I always imagined she was chasing a chipmunk that was desperately extending its burrow a few inches ahead of her. 

    We fell into a routine: three walks per day, including a visit to a park where she could go off-leash. That meant I got to know some beautiful conservation land at all seasons. As she enjoyed the scents and greeted the other dogs, I had a chance to observe the landscape around us. My sustainable gardening approach was born partly from that daily time outdoors.

Sampling the breeze at the dog park

    Although our yard was completely enclosed by fences, I think Nadia was just humoring us by staying inside them. One day she left the dog park without me when two big wolfhounds frightened her. I searched frantically. When I got home, she was inside the fenced yard, and the gate was closed. We never found out how she got inside.

    While I gardened, Nadia kept me company, lying on the porch surveying her domain or strolling around the yard, occasionally checking on my progress. 

Nadia helps with a study session

Rabbits frightened her, but she loudly repelled any dogs or cats attempting to breach our perimeter. At first the sight of me digging would inspire an irresistible desire to join in. As she got older and calmer, I was able to persuade her that I’d rather she didn’t help.

    Nadia enjoyed zestful good health until age 15. Then she started to slow down and developed medical problems that afflict older dogs. In her last few months, she had little appetite and lost 15 pounds. It was so sad to see our old friend confused, anxious and uncomfortable. Now I picture her young again, playing in Elysian fields. Her spirit is still very much with us. 

 

The pawpaw patch

 A few Octobers ago, my next-door neighbor asked one morning whether I’d heard cats fighting in the backyard the night before. He’d been kept awake by animals screaming near the fence that divides our properties. I went to check out the area and found broken branches in a pawpaw tree. My theory is that raccoons were fighting over the ripe pawpaw fruit.

Pawpaws--raccoons love them

    Pawpaw (Asimina triloba) is America’s largest native fruit. I highly recommend this tree for its decorative appearance as well as its fruit! I planted a young sapling about ten years ago. By sending out root suckers, it’s grown into a patch about 12 feet wide and tall. The tree’s large leaves give it a tropical look.

Pawpaw trees add zing to the landscape with their large leaves

    Until the “fighting cats” episode, I didn’t realize the tree was bearing fruit. That day I noticed some yellow fruits that had fallen to the ground. Looking up, I saw clusters of green ones on the branches. 

    Pawpaw fruits look a bit like mangoes. Mine don’t get more than four inches long. The smooth skin covers yellow custard-like flesh surrounding up to a dozen large seeds shaped like lima beans. 

Pawpaw seeds

The fruit’s delectable taste is somewhere between banana and mango. 

 

Pawpaw fruit is a seasonal treat

     Birds, opossums, and raccoons enjoy pawpaw fruit, and they’re great at sensing when it’s ripe. That means I have to be on my toes to share in the harvest. During last year’s drought I got none. I suspect that thirsty animals grabbed the pawpaws as soon as they were edible. This year I’ve snagged a few ripe ones from the ground under the tree.

Ripe pawpaws

    Most people in the Northeast haven’t encountered pawpaws except in that old song, “Way Down Yonder in the Pawpaw Patch.” The reason for the lyric “Picking up pawpaws, puttin’ ‘em in your pocket” is that the fruit isn’t ready to eat until it falls to the ground. Eaten too soon, it has a mouth-puckering taste like under-ripe kiwi fruit. 

     We don’t find pawpaws at Whole Foods yet because the ripe fruit doesn’t last long enough to ship to market. Kentucky State University’s Cooperative Extension Program is working on this; they’ve made pawpaw research their specialty. Their nutritional analysis puts pawpaws’ antioxidant content equal to cranberries’.

    Pawpaw is a tree of the continental interior. It likes humid summers and dislikes coastal breezes. Native Americans are credited with having spread pawpaws from Canada to the Gulf Coast. Washington and Jefferson enjoyed the fruit, and it nourished the Lewis and Clark expedition when they ran out of food.
 

"Hungry? Try the pawpaws over there."

    The National Park Service reports that pawpaws are the most common saplings in their forest monitoring plots around Washington D.C. This is partly because deer don’t like pawpaw leaves, which contain nasty-tasting insecticidal chemicals called acetogenins. When other trees are decimated by overpopulated herds of hungry deer, the pawpaws are left to soak up the sunlight. 

One deer is charming, thousands defoliate the landscape--photo merrilyanne

     Suppressing wildfires also favors pawpaws, which are less fire-adapted than other trees. Someday we may see pawpaws where we used to see maples and oaks.

Not all the perfumes of Arabia can wash this little leaf clean

At a meeting of the Wayland Garden Club last month, a gardener reported tar spot fungus on her Norway maple leaves and concluded that this meant she had to remove all the leaves from her property. She reasoned that they couldn’t be used for compost or mulch for fear of spreading the fungus to her lawn and garden. 

Are leaves infected with fungus harmful to other plants?

    You too may have noticed that Norway maple leaves have developed black spots, turned brown and started to fall much earlier than usual. 

Black tar spots on Norway maple leaves

You could imagine that the trees are dying. Fortunately or unfortunately, the fungal infection is just cosmetic. This year’s very wet spring gave a boost to various fungi, including those that cause both tar spot and anthracnose, another fungal condition that causes leaves to brown and drop off, but the trees will leaf out again next spring. 

This Norway maple's leaves have prematurely turned brown and started to drop off

You don’t have to protect other plants from contact with the infected leaves.

    I say fortunately or unfortunately because I’m ambivalent about harm to the Norway maples that line our streets. Like many cities, mine used to favor tall, graceful elms as street trees. 

American elms in Central park

Dutch elm disease, another much more lethal fungal disorder originally from Asia, arrived in New England in 1928 and burst out of control during World War II, when attention to containing its spread was diverted to war efforts. To replace the dying elms, the cities planted Norway maples. They were tough enough to thrive in urban conditions. What could go wrong?     

     Eighty years later, we’re dealing with the consequences of this decision. Free of the competitors they faced in their native range in Europe and western Asia, these trees have become invasive in North America. 

Norway maple in flower, its prettiest time-photo Daniel Case

Since 2009 it’s been illegal to sell or plant them in Massachusetts.

    When we moved into our house in 1985, we had Norway maples as street trees (still present), large specimens stood in neighbors’ yards, and a volunteer thicket of them grew behind the back fence. Now there are fewer Norway maples around us, but I still pull hundreds of their seedlings from my planting beds every spring.

Norway maple seedlings: there are always more coming

    Norway maple has long been my most hated tree. I’ve often wondered how I’d feel if a pest finally came along that could kill them all. The Asian long-horned beetle, which enjoys munching maples, looked like a good candidate. 

Asian long-horned beetles on a maple. This menace hasn't reached my yard yet-photo USDA.

I admit it’s a thrill to see the tar spots inflicting Norway maples and bypassing red maples, a near relative that is native, non-invasive, and less susceptible to the fungus.

Red maple leaves free of fungus

    Call me a wimp, but I can’t wish all those Norway maples dead. They’re a menace, but they’re still providing us with “environmental services” such as sequestering carbon and cooling and cleaning the air. Their dense shade is a bane for gardeners but very welcome to drivers seeking parking places on hot days. Let’s say they have the defects of their qualities. They’re tough, hardy, and good at reproduction. Can we, who planted them, hold them responsible?

Winged maple seeds are called samaras

 

A fair trade

Last weekend I attended a plant swap at New England Wild Flower Society. The society invited members to dig up some plants we could spare and bring them to trade with fellow gardeners. This turned out to be a lot of fun.

NEWFS's Garden in the Woods is a fabulous resource in Framingham, MA

    Each participant brought at least one plant, natives preferred but not required. We were each assigned a group number, 1 through 4. The offerings were varied, from garden favorites quite familiar to me to native plants for special locations such as swampy areas. When everyone had arrived and our group number was called, we dashed to the plant tables and each chose one plant. We took turns choosing until the plants were gone.

    I’d brought two wild gingers (Asarum canadense), two white-flowering phlox (Phlox maculatum ‘David’), a white bleeding heart (Lamprocapnos spectabilis ‘Alba’), and a goldenrod (genus Solidago) whose forebears I grew from seed years ago. 

Phlox 'David" blooms in mid- to late summer

     As I placed my offerings on the tables, I realized I’d be embarrassed if nobody chose them—like not being picked at a dance. I was relieved that they all found homes by the last round. Next year I’ll pot some plants in spring so they’ll look more appealing for the swap at the end of the summer.

    I came home with eight plants: a beautiful purple heuchera, a switchgrass (Panicum virgatum), a foxglove, a blue false indigo (Baptisia australis), two blazing stars (Liatris ligulistylis), a showy goldenrod (Solidago speciosa) and an Allegheny monkey flower (Mimulus ringens).

This well-grown heuchera was a prize

Besides a fun “shopping” experience and a chance to meet like-minded gardeners, the swap met two sustainability goals for me. First, I could be sure that none of my fellow NEWFS members had been spraying their plants with neonicotinoid insecticides before bringing them to the exchange. Neonics persist for a long time, but my hope was that these plants were either seedlings from the gardeners’ original plants, or they’d been around long enough to have outlived any pesticides they might have encountered at a nursery when they were young.

Native plant enthusiasts know not to poison pollinators with neonics

    Second, a swap like this gets around the carbon cost of garden center plants. Annuals and perennials we buy locally zip around the globe before they end up in our shopping carts. Growers may buy seeds from importers who source seed all over the world. They use tissue culture products imported from South Africa, Holland, Turkey, and Poland (tissue culture converts tiny pieces of plant tissue into large numbers of genetically identical plantlets). Large plantations in Costa Rica and Ecuador with space to maintain supplies of stock plants send unrooted cuttings for regional growers in the US to root and grow to saleable size.

Plants growing from tissue cultures-photo Daderot

    To produce high-volume annuals like petunias, breeders send cuttings to specialists at a rooting station, for mass production. A broker shopping on behalf of wholesalers or garden centers fills orders with rooted cuttings from multiple rooting stations.

    Unlike these international travelers, perennials from the plant swap really do come from the local area. And they’re free! A good deal all around.

This goldenrod grew up in my yard

Hell and high water

Photos of Houston afflicted by Hurricane Harvey reminded us of the worst that stormwater can do. It’s been pointed out that Houston’s unrestrained development created a set-up for flooding.

Flooding in Houston

Developers have been building in flood plains and paving over wetlands and prairies, reducing the chance for rain to soak into the ground. Smarter urban planning could have lessened the catastrophic effects of the hurricane.

Wetlands around Houston used to absorb stormwater--photo by Daniel Ray

    Did you know that China is a leader in this environmental area? They’re developing “sponge cities,” engineering ways to keep rainwater for use by water-poor cities, rather than letting it run off.  Besides cutting down on impermeable paved surfaces, they’re collecting rainwater in ponds and tanks and circulating it into the cities’ water supplies, either for non-potable uses or purified as drinking water.

    I hope it never happens, but if we got 50 inches of rain (a year’s worth) in a few days, the amount that fell on Houston, we’d want to let it soak through every possible surface.

Our deck and stone path, wet but permeable

Even without a huge hurricane, it’s better to keep rainwater on your property, because if it rushes down the street, it carries pollutants with it into nearby waterways. Here are some ways we gardeners can make our yards more sponge-like.

•    Make hard surfaces permeable. This is probably the most important change you can make. For us, the driveway is the main impermeable surface. By replacing a section of our asphalt driveway with porous paving material, we’ve enabled water to soak into the ground. 

Water sinks into the darker porous paving

A nice-looking alternative is to make a driveway out of stones with spaces between them where water can soak in. 

Paving stones let water soak through

Spaces between the stones of our new walkway similarly allow water to reach the soil below.

•    Direct water where you want it to go. If you’re an enterprising digger, you can create swales—basically trenches--to send water to your garden beds or to low-lying areas, where it will gradually percolate into the soil. 

Bioretention swale in Seattle during a 100-year storm

David Del Porto, an environmental visionary who designed an eco-friendly house and landscape called the Urban Ark 30 years ago, told me he used this approach to direct rainwater from his roof to the right spots in his vegetable garden, obviating the need for irrigation with purified drinking water. 

•    Plant a rain garden. This is a shallow depression, ideally at the lowest area of your yard, where water can collect and filter into the soil. Plants in the rain garden will soak up water and help purify it. Heavy soils may need to be amended with sand or gravel to make them drain faster in the rain garden; our sandy soil drains fast already.

A rain garden in Leeds, MA--photo U.S. Air Force

I like to think that we designed a rain garden without meaning to, because the land slopes down from the fence lines, making the center of the yard a collecting site for rainwater. I’d still plant a rain garden if I had a place for it. It’s a great excuse for a new planting project.

Gypsy moth: more complicated than you'd think

While waiting last week for my computer to return from urgent care, I contemplated a talk about biological controls by Joseph Elkinton, a professor of environmental conservation at the University of Massachusetts, that I heard last November. 

Gypsy moth caterpillar

    What Elkinton said about the history of gypsy moth in North America turns out to be unexpectedly relevant. We had a gypsy moth surge in 2016, and this year there has been significant defoliation by gypsy moth caterpillars, especially in southeastern Massachusetts.

Voracious gypsy moth caterpillars shred leaves

    A complicated web of factors influences the gypsy moth population. It all goes back to acorns.

    Gypsy moth (Lymantria dispar), native to Europe, was introduced to Medford, Massachusetts by Étienne Léopold Trouvelot, an astronomer dabbling in silk worm breeding. He thought he could cross the gypsy moths with native silk moths to produce silk in the US. The insects escaped from his home in the 1860s, and over 50 years they slowly established themselves in the wild. They’ve spread as far as Minnesota and North Carolina.

Life stages of the gypsy moth

    Elkinton explained that until 1989, gypsy moths experienced population outbreaks about every 10 years. Throughout the twentieth century, predator insects were introduced in hopes of controlling the gypsy moth population, but none did enough.

Predatory wasps kill caterpillars, but not enough

     Meanwhile, research into the ecology of the gypsy moth uncovered a system of natural controls. Robert Campbell of the US Forest Service found that the white-footed mouse was the most significant predator of the caterpillars, with birds less of a factor.

White-footed mouse, Peromyscus leucopus, in captivity

     Mouse populations rose and fell with the supply of their main food, acorns, which fluctuated with weather conditions. The mice couldn’t expand their population enough to control gypsy moth outbreaks, when caterpillar numbers spiked exponentially.

    Outbreaks were brought to an end by Nuclear Polyhedrosis Virus (NPV), which eventually killed up to 99 percent of the horde of larvae.

    This cycle continued until another accidental foreign introduction in 1989: Entomophaga maimaiga, a Japanese fungus. Infected by the fungus, gypsy moth caterpillars suddenly died all over southern New England.

    So with mice, viruses and fungi controlling its population, why is gypsy moth surging again? The levels of fungus are highest in wet years. Last year’s severe New England drought allowed the gypsy moth population to escape from its fungal control. This summer, caterpillars chomped foliage until June, when they started to die off. Caterpillars examined by Elkinton’s team showed a combination of viral and fungal infections. Wet weather had turned the tide.

    This means, thank heavens, that we don’t have to make the difficult decision whether to spray for gypsy moth.

    The future outlook for New England trees is mixed. Gypsy moths won’t die out completely, and our trees face a number of stresses from drought and other nonnative insect attacks. A tree can survive one defoliation, but repeated losses deplete its energy stores. Elkinton worries about major losses of native oaks, which the caterpillars particularly enjoy. Then what will happen to the white-footed mice?