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Sunday, November 12, 2017

Picky eaters

Something I learned from entomologist Doug Tallamy’s book Bringing Nature Home is that most insects specialize. Ninety percent of herbivorous insects depend for food and shelter on a few plants they coevolved with. This insight is directing me toward different plant choices.

    I used to think that leaf-eating insects ate any leaves they could get. Tallamy explains that, on the contrary, over the millennia insects have survived by tailoring their behavior and physiology to be able to sense and locate a few plant species. 

Not just any leaf will do for food

They’ve synchronized their life cycles with the plants’. They’ve developed ways to get around the plants’ defenses. As they’ve invested in these food sources, they’ve become less able to live off others. That’s why most need plants from their local region and can’t eat plants from other parts of the world.

North American native insects can't eat plants that originated in Asia

    This year I’ve expanded my collection of milkweeds for monarch butterflies, the poster children of insect specialization. Monarch caterpillars have evolved to be able to eat milkweed leaves, which contain defensive chemicals called cardenolides that make the caterpillars and adult butterflies poisonous for other animals. 

A monarch on showy milkweed (Asclepias speciosa)

When eggs laid on milkweeds hatch, the caterpillars have the food they need to grow and metamorphose into another generation of beautiful adult monarchs.

    Monarchs are now under great stress. They need to fly from their winter home in Mexico to summer habitat in the US. 

Wintering in Mexico-photo Steve Bridger

Here they find less and less milkweed because of herbicides such as Roundup (glyphosate) that are widely used in industrial agriculture. Organic farmers make a point of leaving weed strips around their fields for the sake of pollinators, including butterflies. Until that becomes universal practice, home gardeners are encouraged to grow some milkweed for the monarchs.

    I started with swamp milkweed (Asclepias incarnata), which turned out to be quite easy to grow. Swamp milkweed’s dusty pink flowers are clearly an insect magnet. Not only the monarchs benefit.

Swamp milkweed attracts lots of pollinators

    This year I tried butterfly weed (Asclepias tuberosa) again. I’d planted this species twice before, only to see it dwindle without flowering. With a sunnier spot and plenty of rain this spring and summer, it didn’t flower, but it seemed to take hold. I’m optimistic about seeing some of the orange flowers next summer.

Butterfly weed, not as easy as I'd hoped.

    I also started seeds of common milkweed (Asclepias syriacus) and planted a couple of seedlings. This could turn out to be a mistake, because the plant is reputed to be quite a spreader. I like the seed pods and the seeds with their parachutes of white fleece, though, and I’m hoping to see some monarch caterpillars on the leaves.

Common milkweed seed pods opening in fall

    As an experiment, I laid a half-open common milkweed pod that I found in the neighborhood on the ground in an open area near some new shrubs. Maybe the wind will pick up some seeds and sow them as it would in the wild.

    I spotted just one monarch butterfly in the yard this summer. I hope she or he will send friends.

Sunday, November 5, 2017

Too many trees

Back in 1997 during a major garden expansion, I had fun shopping for trees with garden designer Betsy Brown. She drove me around Massachusetts to pick out saplings of favorite tree species I’d dreamed of including in my ideal garden—in retrospect, too many of them. Betsy artfully placed new trees and shrubs in open ground we’d annexed, standing back to direct the landscape crew to move them a few feet this way and that until they were spaced just right.

    The new trees on the berm at the back of the lot looked a bit forlorn with lots of mulch between them. Back then it was hard to imagine that they’d ever fill the empty space.

Newly planted trees on the berm, 1997

Well, twenty years later, they’ve done that and more.  First the young trees grew taller and fuller. Then they reached out and touched branches with their neighbors. 

Touching shoulders in 2006

This year I looked at some photos and realized the trees on the berm were crowded. We’d planted them too close together.

This week--too crowded

    When my friend Marlyn invited me on a tree walk through Newton Cemetery, I got to see a more farsighted planting approach. Groves and single trees were amply spaced to create painterly vistas. I observed what several of my trees would look like if they’d grown up with unlimited room to spread out and no nearby competition for sunlight and moisture.

Japanese umbrella pine at Newton Cemetery
And trying to grow in my crowded yard


     I’ve taken down some trees over the years to reduce crowding. Betsy’s original design involved a circle of lawn lined by four graceful white-flowered redbuds (Cercis canadensis f. alba). I’ve since regretfully removed two of them. When they were young, their lithe branches lined with tiny white blooms in May looked like dancers in a green woodland. 

One of the redbuds in its early days

Unfortunately, the trunks couldn’t grow straight because of expanding shade from taller trees.  

One of two remaining redbuds, reaching for sunlight

As the ill-fated pair leaned farther and farther out over the lawn and shaded out perennials I wanted to grow nearby, I made up my mind that they’d have to go. Their stumps still make me feel like an assassin, as do the empty spaces left by hemlocks we took down this year.

What terrible person cut down this tree?

    At this point there’s no easy way to make more room for the trees. I can let the inter-weaving of branches continue or make more hard choices and edit out more trees. As I plant in the empty space left by the hemlocks, I notice that as they expanded, they distorted the growth of surrounding trees. A Hinoki false cypress (Chamaecyparis obtusa) has no living branches on one side where a hemlock muscled in on it. 

Branches died on the side where the hemlock shaded out this tree

    If I did remove trees from the berm, the ones remaining wouldn’t have symmetrical shapes. Once they’ve shed their needles because of too much shade, branches of these conifers won’t send out new foliage.

    What to do? I’ll probably delay action until one of the trees dwindles or becomes a danger and has to come down. It hurts to cut down trees.

Attention friends: I'll be speaking at the Massachusetts Horticultural Society's Ecological Gardening Symposium next Wednesday, November 8, at Elm Bank in Wellesley, MA. Here's a link to the program information. I'd love to see you there.

Monday, October 30, 2017

Beware of Greeks bearing gifts

One of my biggest gardening mistakes was planting smooth Solomon’s seal (Polygonatum biflorum). This seemingly modest woodland plant aims for world domination. Now I’m trying to beat back its onslaught.

Smooth Solomon's seal emerges in spring

    I first encountered smooth Solomon's seal in the shade plant section of my favorite garden center. At the time I was coming to grips with the fact that I was gardening in shade. I was delighted to discover lots of plants with pretty foliage in a shady corner at the far side of the sales area. Smooth Solomon’s seal caught my eye because of its arching stems, shiny leaves, and pendant cream-colored flowers. 

Seemed like an understated, elegant woodland plant--photo Peter Gorman

I didn’t seek out native plants at that time, but since it was a North American native, that must mean it wouldn’t run wild, right?

    For several years I thought I’d picked an excellent plant for shady areas where nothing else wanted to grow. About ten years in, though, I noticed that smooth Solomon’s seal was showing up in every shady part of the yard—and that’s most of my garden. Its little blue fruits must have been making their way to new territory. In retrospect, I might have been safer with an attractive Eurasian cousin, fragrant Solomon's seal (Polygonatum odoratum ‘Variegatum’), which has a pretty chartreuse border around its leaves and seems to be less spreading—so far.

A more sedate Solomon's seal? Or crouching to spring

    It’s not too hard to dig out smooth Solomon’s seal. When you do, one reason for its success in dry soil becomes obvious. It has big fleshy rhizomes, underground storage organs that look capable of storing plenty of water and nutrients. 

Rhizomes store supplies for hard times

I’ve learned not to throw these or the blue fruits on the compost pile, because both produce new plants. Moving compost around, I may have unknowingly carried them to new areas of the yard. 

Fertile fruits of smooth Solomon's seal

Instead I now send them out as yard waste, to be cooked at weed-killing high temperatures at the municipal composting site.

    There’s a crabapple tree that I look at every day from our kitchen windows. I’d sure like to grow other shady woodland flowers under it, not just smooth Solomon’s seal. 

A pot of elephant ears attempts to disguise rampant smooth Solomon's seal under the crabapple

What holds me back from ripping it all out is the fear that I’ll kill the tree in the process. I once read a sad story about a man who killed a beloved dogwood by digging among its roots to surround it with daffodil bulbs, and I think I executed a venerable Japanese andromeda (Pieris japonica) when I pounded plastic edging through its root zone.

     So I’m removing the unwanted smooth Solomon’s seal cautiously, bit by bit. Last spring I dug out a wedge-shaped patch of it from the tree trunk to the drip line. This fall I did the same in a slightly larger wedge, arguing that the tree was ready for this because of our wet summer. Time will tell whether I went too far.

A section cleared of smooth Solomon's seal-- for now

    The main remedy will be to plant something else that can stand up for itself in place of the plants I tore out. Smooth Solomon’s seal abhors a vacuum.

Attention friends: I'll be speaking at the Massachusetts Horticultural Society's Ecological Gardening Symposium on November 8 at Elm Bank in Wellesley, MA. Here's a link to the program information. I'd love to see you there.

Monday, October 23, 2017

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.

Sunday, October 15, 2017

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 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. 


Sunday, October 8, 2017

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.

Sunday, October 1, 2017

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