Farewell to a tree I loved to hate

I'll be presenting a free Green Newton lecture on Beautiful Sustainable Gardens at the Newton Free Library this Monday June 10 at 7:00 p.m. See you there! 

In April, I received a letter informing me that one of our two street trees was going to be cut down. I’ve been wanting to get rid of this tree for years. It was a Norway maple (Acer platanoides) that had been losing branches over the years, until all that was left was a large limb angling toward the house. 

 

The doomed Norway maple in May

     
     We’re on the side of the street with the power lines, so over the years the utility company has been hacking away at this tree and its partner at the other end of our street frontage. A few years ago, I asked the city to inspect the tree because I thought it was liable to drop a heavy branch on a pedestrian or a parked car. At that time, they found it was still sound. Now, the letter said, it had “significant defects.”
 

Marked to be cut down

     The reason I resented this tree wasn’t just its species. Yes, I dislike Norway maples for their fecundity and voracious shallow roots. This tree also cast dense shade over the front yard. It had limited what I could grow under its branches to the standard broadleaf evergreens you see everywhere in the neighborhood. A couple of years ago I added an oakleaf hydrangea (Hydrangea quercifolia) that livened things up a little, but still.

Ho hum boxwood, Japanese pieris, and mountain laurel

    One morning last week, two trucks arrived, and the urban forestry team took down the tree. I darted in and out of the house taking pictures to document the big event. 

Avoiding wires to saw off chunks

A bucket truck allowed a man with a chain saw to maneuver around the wires and cut the tree apart piece by piece. Another man operated a giant arm picking up large branches to haul back to the city yard for chipping. 

Future wood chip mulch

After half an hour, all that was left was the newly cut stump.

Its center was hollow

    I had six weeks to anticipate it, but this event caught me off balance. I wasn’t prepared to be sad to see the Norway maple go. Although I’d wanted it gone, seeing it chopped up so fast reminded me of how it had stood there patiently through blizzards, hurricanes, droughts, and nonnative insect attacks. The tree was misshapen at the end, but that comes to all who live to old age.

    The other surprise was my lack of ideas for what to add to that corner of the front yard. Without the tree’s shade, there are so many more options, including native shrubs I’d like to try. I’m not used to selecting plants for sunny spots. I’ve often thought that more highbush blueberries (Vaccinium corymbosum) should be grown in front yards. They have small neat leaves like privet (Ligustrum vulgare) that turn a pretty red in fall. 

Blueberry foliage turns red in fall

Unlike privet, though, they’re natives and not invasive. It would be a friendly gesture toward both birds and walkers to offer blueberries along the sidewalk.

Neighbors could pick blueberries as they passed

    When it’s too hot to work outside this summer, I’ll consider what else I could plant in the new sunny clearing this fall.

What goes with chartreuse?

After the beautiful elms that lined our streets succumbed to Dutch elm disease in the mid-twentieth century, my town, like many others, thought they’d found great street trees to replace them: Norway maples (Acer platanoides). 

Surviving elms in New York's Central Park

After all, the maples were tough, adaptable growers that could survive the tight root space, thin, rocky topsoil, and plentiful road salt that our narrow curb strips offered.
    
    In one way, choosing these maples was a success. Almost all our streets are now lined with mature specimens. Over their lifetime they’ve rolled with the punches, putting up with limbs torn off by ice storms and passing trucks, finding water by pushing their roots under the sidewalks into lawns and garden beds, growing around holes gouged in their canopy by pruning around power lines.

Norway maple street tree-photo Famartin

    The problem with these nonnative trees is that they’re too successful. Each tree produces thousands of viable seeds every spring, packing pairs of them into the helicopter-like samaras that we see twirling to the ground. 

Winged seed pods of Norway maples

They lie in cracks in the sidewalk, in garden beds, and on any bare soil or pile of organic debris. It seems as if most of those seeds succeed in producing seedlings the following spring. 

    This is the time of year when gardeners like me become obsessed with weeding out those seedlings. We know that by next year, this season’s tender little sprout will have grown a woody stem and sent down a deep root. If we don’t catch them this year, they’ll be harder to pull with every passing year.

One-year-old Norway maple seedling, left, with this year's on right

    When we moved into our house, a dense thicket of Norway maples that soon reached 20 feet high grew behind the back fence, just because our neighbors had left some seedlings alone to grow. The trees make dense shade, their shallow roots crowd out competitors, and they exude allelopathic chemicals that keep other plants from thriving in their vicinity.

Norway maples shading the backyard in the mid-90s

Luckily for my garden, we were able to remove those trees. Their relatives have continued to colonize the city, though. 

    When the Norway maples flower at the end of April, my heart softens toward them, despite my struggle to curb their reproduction. I love the lacy silhouettes the flowers make against the street lights after dark. The rosettes of chartreuse flowers and tiny new leaves are a heartening sight when many trees haven’t yet put out any foliage. 

Norway maple in bloom

A cloud of yellow-green covers the whole city, reminding me of Robert Frost’s line, “Nature’s first green is gold.”

Norway maples paint the landscape a vibrant pale green

    In recent years, our city has gotten wise. Where street trees have died or been cut down, our urban forestry director now chooses to plant a range of resilient tree species—but no more Norway maples. Soon we’ll have a diverse mix of street trees that are less inclined toward world domination. Meanwhile, we should remind ourselves when choosing spring-blooming bulbs and shrubs that they’re going to flower against a chartreuse background. Whether we like it or not, those maples won’t disappear anytime soon.

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

 

Invasives are here to stay

I hate to say this, because I think it will make some people mad, but I don’t think there’s any hope we can eradicate invasive nonnative plants from our landscape.

    This is an area of hot controversy. Many admirable volunteers spend their weekends pulling out invasive plants that grow on public land. 

Volunteer at a garlic mustard pull in Washington state

These are plants that cause environmental damage, out-competing natives and endangering local insects and animals because they don’t provide them with food and shelter they need.

    People who devote their time to eradicating invasives reject tolerating these plants. But there is another perspective. As Hope Jahren points out in Lab Girl, “Humans are actively creating a world where only weeds can live and then feigning shock and outrage upon finding so many.” Cities are hotter, dryer and windier than the countryside they replace, and we keep tearing up the ground with new building projects. No wonder only the toughest plants survive.

    Even if public land were cleansed of invasives, it doesn’t exist in a vacuum. At the Garden Bloggers Fling in Minneapolis, I heard that the Eloise Butler Wildflower Garden  had to have volunteers scour garlic mustard (Alliaria petiolata) from a buffer zone around the 15-acre garden to keep it from migrating into the reserve. Yet every year their staff still has to patrol the property for garlic mustard seedlings. 

 

Native black-eyed Susans and bee balm at Eloise Butler Wildflower Garden

    Garlic mustard crowds out other herbaceous plants and excretes antifungal chemicals that disrupt connections between soil fungi and native plants, suppressing growth. 

Garlic mustard in bloom

What is the chance that every Newton homeowner will police her property and catch every garlic mustard plant before it sets seed? Not since Maoist China has social engineering on that scale been feasible.

    Here’s a case in point. Across the street from my house, a neighbor’s fence runs parallel to the sidewalk. In the few inches of soil between the fence and the pavement, a panoply of invasives has taken root. There’s garlic mustard, Oriental bittersweet (Celastrus orbiculatus), Norway maple (Acer platanoides), and black swallowwort (Cynanchum louiseae). Yes, I uproot them as I walk by. But all over town the same situation is occurring, and in most places no one notices or cares.

Oriental bittersweet

Norway maple

Black swallowwort

So if we can’t kill all the invasives, what are we supposed to do? Are we willing to let them take over and accept simplified landscapes without the biodiversity needed to maintain native animals? 

Actually we already have. A stroll in any local park confirms the presence of large populations of invasives. 
    
     I may be unrealistic, but I prefer to think that by planting natives in our own yards and fostering their growth on public lands, we can restore some balance between natives and aggressive nonnatives. If not, we’re going to spend all our gardening time at war, and that’s a condition I can’t accept.

Native red oak in my yard. This is a popular host plant for native insects

Policing or editing?

Where should weeding stop? I confess I have trouble stopping myself from pulling out certain weeds, even when they’re not on my property.

One I missed this spring

            My number one target is Norway maple (Acer platanoides). Starting in April thousands of its offspring peek through the groundcover in front of the house, sprout in the compost pile, and even poke up in compacted areas of the lawn. As I move around the garden in spring, I clutch an expanding bouquet of the little seedlings. If I miss them their first year, they’ll be back the next spring woodier and harder to pull out.

            Cities chose Norway maples as street trees because they can tolerate urban conditions. Can they ever! Fence lines and hedges around the neighborhood bear witness to what happens if you ignore their seedlings for a few years—they soon grow tall and out-compete everything below, blocking the sun, hogging the water, and spreading their phytotoxins, chemicals they exude that prevent other plants from growing. 

            I find it hard to keep my hands off the multitudes of Norway maple seedlings I pass in other people’s front yards as I walk my dog. Ailanthus altissima 
(tree of heaven, the tree that grew in Brooklyn), another rapacious grower, also makes me want to yank it out. 

            But how would I feel if someone else weeded my garden without my permission? Outraged and insulted. So I try to hold back. I don’t always succeed.

            All this weeding makes me ask whether I’m trying to police the world. Gardeners reserve the prerogative to decide what grows in their gardens. Outside the garden gates, though, should we stay out of it and let the strong survive? 
            Roger Swain, whom you may remember as the host of the PBS show The Victory Garden, wrote about “editing” a patch of woods on his New Hampshire farm. He subtracted trees and shrubs in March to incline the population toward the native plants he wanted to foster. This seems like a sane approach to the plant world. But when he was in Lexington to film the TV show, I wonder if he found himself twitching out Norway maple seedlings.