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Archive for the ‘Plants’ Category

On Saturday the Times published two letters that responded to its recent op-ed piece by Thomas Lee Ogren on trees, pollen, and allergies.

One reader, Christine Lehrer, wrote:

Honeybees collect pollen from the very trees that are causing all the sneezing and runny noses. By taking a spoonful of honey daily, approaching and during allergy season, you inoculate yourself against the offending pollen and greatly reduce your allergic reaction.

Another, Joan Edwards, wrote:

Plants with showy colorful flowers like magnolia, black cherry, redbud and flowering dogwood … make pollen that is designed to affix to their pollinators. Their pollen is sticky, produced in small quantities, and large so it is less likely to be blown in the wind, where it can be inhaled by an unsuspecting passer-by.

Both of these cannot be true. My money is with the Edwards: Bee-pollinated trees don’t bother to release the kind of pollen that makes you sneeze, and wind-pollinated plants don’t bother to attract bees. (There may be belt-and-suspenders plants out there that can be pollinated by wind but would like also to be pollinated by bees, but this non-botanist isn’t aware of them. Readers?)

So by planting only insect-pollinated trees and the female cultivars of wind-pollinated trees, we can reduce pollen counts. Good information, as far as it goes, but neither Ogren nor Edwards successfully addresses the other qualities that urban trees require. Ogren writes:

In New York City, street trees are selected only for their hardiness in winter; their resistance to disease, insects and drought; their ability to withstand smog; and their size, shape and color.

Even when selecting “only” for those criteria, the trees that pass muster make up a pretty short list.  Adding a new criterion will only make the list shorter. And in fact, very few of the trees that Ogren and Edwards recommend would perform well as street trees.

It turns out New York’s criteria make sense.  Size, for example, matters. A big tree does more to keep a city cool and clean than a small one does.  It casts more shade, transpires more water, absorbs more noise, and (if its leaves are fuzzy) traps more particulates. Plus, a sidewalk tree’s lowest branches have to be higher than a tall pedestrian’s head, so the tree has to be large enough that it can be limbed up without looking like a broken umbrella.

Trouble is, most big trees are wind-pollinated. (Evolutionary biologists, pitch in here: Is it because more insects fly at dogwood-height than at oak-height, or are there some other phenomena at work? What is it that the tall insect-pollinated trees — tulip poplar, cucumber magnolia, caltalpa, horse chestnut — have in common?) Whatever the benefits of planting only the kinds of trees that don’t release a lot of pollen, our urban forests would be poorer for it, and our cities would be hotter, to the detriment of trees and people alike.

Instead of banning wind-pollinated trees altogether, what about mapping prevailing spring winds and vulnerable populations (schools, hospitals?), and designating zones in each city where only female and bee-pollinated trees would be planted? If we can put some allergists and public health specialists in the same room as some planners and urban foresters, we might get somewhere on this.

In the meantime, stir a little local honey in your tea. Probably won’t help. Can’t hurt.

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Sign

As I was driving down a Cambridge street last Tuesday this scene caught my eye. My heartfelt good wishes and thanks to whatever forward-thinking kind soul who planted these crocus bulbs and let them naturalize through the lawn; after a long and cold and grey winter they were balm for the eyes.

Apologies for the small image size — the light was about to turn green, so I had to snap before I could zoom in.

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Last week a friend mentioned seeing a yellow-flowering shrub on the VFW Parkway in Boston. It reminded me of the show of Hamamelis that used to appear outside of the Harvard Business School’s Baker Library back in the early 80s; when I first saw it (this was a few years before I became a landscape architect and learned what Hamamelis was) I thought a bank of Forsythia was blooming in February.

Saturday I was in Cambridge, and drove down a street that used to be on my route home from work at CRJA. As I turned the corner, this sight greeted me.

This street runs roughly east-west, and with buildings on both sides gets a slice of sun in the middle of the day. The sycamore maples further along the street add a bit of dappled shade to that slice, too. These Witch Hazels don’t seem to mind. And they have the room they need to spread and fill out their characteristic fountain habits.

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Cattleya in bloom; Ripsalis in background


Another grey and cold day in a long, cold month. Going to my desk and working is a good antidote to the gloominess, especially when the Cattleya next to my drawing board blooms (as it did last fall), or the Ripsalis in the window each January reliably turns from a mop of green string into a mop of green string and yellow confetti. Each plant has its own delicate flower fragrance, which rests quietly in the air until someone walks through the room and stirs up faint currents of deliciousness. It’s a good reminder to use scented plants in the landscape.

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I just wrote a post on Herbie, the champion American elm in Yarmouth, Maine, that was taken down last week after a life that spanned more than two centuries. The post, at Taking Place In The Trees, included several photos I took the day before Herbie came down. In his prime, Herbie was the largest American elm in New England — 110′ high, 120′ wide at the crown’s widest point, and 20′ in girth. When I saw him, more than half of his largest limbs had been removed, but the tree’s presence and majesty were unmistakable.

Herbie the American Elm, in his prime.


A field count of the rings on Herbie’s trunk indicated that the tree was at least 212 years old. This was a tree that largely defined the genius loci of its neighborhood. It filled the corner of a private yard and marked the intersection of two streets; it cast high shade over a wide and fortunate area.

It’s not difficult to extrapolate lessons from Herbie’s presence and longevity, lessons that might inform how landscape architects design and advocate for planting spaces. I can think of these lessons:

1. Plant trees! They provide cover, coolness, oxygen, and identifiability to a place.

2. Plan for the long term — aim to foster a tree’s growth for decades, not just for years.

3. Design for root space — bare-root transplanting of large trees shows us how trees benefit from space in which to grow, and how far from the trunk their roots need to grow to add crown growth. Push those developers, homeowners, and city agency officials to allocate more space for subgrade growth; it’ll pay off in happier, healthier trees, and broader shade canopies.

4. Remember how big trees want to get. Putting a large-scaled canopy tree in a slot of soil better used for skinny grasses won’t give you the tree you’re looking for; it’ll give you a tree that whimpers for a few years, declines, and then dies. Scale your trees to your site (aiming for as big a planting site as possible — see 2. and 3.)

5. Shoot for size. People love the giant, and are more apt to preserve and take what they love. A large tree builds its own constituency, which helps when you’re trying to keep nature from being overtaken by pavement. If you want people to engage with nature, give them something with which it’s easy to engage. (Keeping in mind 4.)

That’s for starters. What other lessons do you see in Herbie’s story?

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The Massachusetts Arborists Association has a new volunteer initiative starting in 2010. They aim to build on the traditional Arbor Day celebration by instituting a statewide volunteer service day on that day, which falls on April 30, 2010.

To get the ball rolling, the MAA is inviting anyone to identify potential tree care projects in their own communities, and then to post those project ideas on the Arbor Day link at www.MassArbor.org. They hope to get ideas from all 351 Massachusetts cities and towns by January 15. From that list, MAA members and member companies will choose projects for their own Arbor Day of Service volunteer effort.

This is a great way for landscape architects to elect projects and for professional arborists to make a contribution, both for the civic good, and for cities and towns to reap the benefits of a concerted professional effort. Safety pruning, tree planting, hazard tree removal, ornamental pruning — a community you drive through daily may have the project that’s perfect for your company to tackle on Arbor Day. To submit a project for Arbor Day of Service consideration by the MAA arborists, visit www.MassArbor.org by January 15, and click on Arbor Day.

Arbor Day is a great way to get all generations involved in plant care.

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Say you’re a growing country club in a nicely-treed community, and you need to enlarge your parking lot. And perhaps you want to lower its grade. The lot has some mature oak trees in it, and they add a certain je ne sais quoi to the scene, so you decide to save the trees by keeping the grade as is around the base of their trunks. You retain the roots and soil with a mortared stone wall. Voila!



Good idea – but woops! The minimum standard for root preservation is to keep 10 inches of root mass diameter per caliper inch of tree. For these trees, that would spell at least 360-inch diameter root masses. Because the trees are so close together, their roots overlap significantly — but still, 360 inches is thirty feet of diameter. This 18-footish enclosure takes a tad too much root; the country club will almost certainly be watching these trees decline and die over the next few years (and they may well drop dead branches onto the parking lot, or cars in it, in the process).

The idea of saving a mature tree is a good one, as long as the tree’s actual requirements for continued healthy life are met. Now that we have the tools to see how large a tree’s root mass really is, it’s much easier to see how big the unimpeded area around it has to be for the tree to survive happily and thrive.

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Aster


So we’ve started down this path, which in a time typically relatively quiet in plant color may not be such a bad thing. These Purple Dome asters gave a great show on one of my projects this fall, and enlivened the scene when other plants were fading to gold and rust.

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other colors

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We’ve all seen photos of grand mixed and perennials borders on old country estates (Gertrude Jekyll, Vita Sackville-West, Beatrix Farrand),

Sissinghurst White Gdn

Vita Sackville-West, Sissinghurst White Garden. Photo by bestfor/Richard on Flickr.


and of sweeps of perennials, grasses and shrubs by the contemporary designer Piet Oudolf and landscape architects Wolfgang Oehme and James van Sweden.
Generous expanses of grasses and perennials at Chicago's Lurie Garden. Plantings by Piet Oudolf; photo by queenjill on Flickr.
They’re dramatic and luxurious-looking, and it’s easy to envision being right there, surrounded on all sides by space and uninterrupted swathes of glorious texture and color.
Sometimes the only space available is quite a bit smaller and more constrained. This past weekend I was walking down a suburban Boston street and found this planting, in which a narrow bed — bounded by fence on one side, driveway on the other — hosts a garden that shows off in every season.
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This plant bed can't be any more than three feet wide, but there is a lot going on in it.


In this climate, plantings that flank a driveway have to be tough. Snow gets shoveled and plowed on top of them, and sometimes it’s best to stick to herbaceous perennials that will die back to the ground and be unharmed by wayward plows.
This garden has a fairly simple palette — Hydrangea, ‘The Fairy’ Roses, Korean Chrysanthemums, Sedum ‘Autumn Joy’, and a carefully pruned collection of crabapples — that works well here. Even if the hydrangeas and roses get clobbered by the plow they’re likely to recover; the sedums and chrysanthemums can be cut back to the ground, and the crabapples are trained to hug the fence, out of the way, making what could have been a winter drawback into a fine asset.
It’s refreshing to see this kind of resourcefulness in what often seem only to be incidental places on a property. This strip isn’t a place in which you’d want to (or could) lounge away the hours, but it shows how varied and texturally exciting even a small space can be.

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