Trees make good urban citizens

The Boston Globe recently checked in on the city of Boston’s promise to plant 100,000 trees by 2020 and found execution woefully lacking. Mayor Thomas Menino made the promise in 2008, responding to concern over climate change. Urban trees across the nation are aging and dying. Planting trees helps absorb carbon and reduce energy use. Last year Boston notched a net gain of only 4,000 trees.

What would Central Park be without its trees? New York is way ahead of Boston in planting new and replacement trees.

    My city's director of urban forestry, Marc Welch, reports he gets more requests to remove street trees than to plant them. Some residents regard trees as pests dropping leaves on their yards. Others want them out because of roots growing into pipes or making driveways and sidewalk surfaces uneven. Some of our street trees need to be removed because they’ve died, falling victim to drought, vehicle strikes, and nonnative insect pests such as winter moth and gypsy moth.

    Marc is pro-tree, though. He and the Newton Tree Conservancy are bucking the trend, planting new street trees since. In my post of May 14, I described the planting process.

Planted last month

    Trees do much more than offer shade in summer. One of my favorite garden authors, Toby Hemenway, describes the many ecological services provided by trees: 

• Creating insect habitat and hunting grounds for birds. One example: as the air warms in the morning, the leafy canopy stays cool longer than the air just above it. Insects swirl around in the layer of warm air, allowing birds to find food.

Cedar waxwing feasting on fruit of an amelanchier tree

• Conserving water. Soil stays moist under the shade of the tree’s leaves, watering plants and contributing to stream flow.

• Filtering groundwater. As leaves transpire, releasing water through pores in the leaves called stomata, the tree cleans out impurities from the water it draws up from the ground. 

• Making rain. Up to half of rain over tree-covered land comes from water transpired from leaves. In addition, pollen and dust that mixes with air as it flows through the leaves form nuclei for raindrops, seeding the clouds.

Trees make rain for the plants and creatures around them

• Harvesting moisture. Fog condenses on cool leaves, gathering water even without rain.

• Sequestering carbon. During photosynthesis, leaves take in carbon dioxide from the air and release oxygen.

• Stirring breezes in summer and blocking wind in winter. In warm weather, convection starts air moving when the tree absorbs sunlight and mixes warm air with cooler air near the ground. A tree can also act as a windbreak, reducing heat loss from buildings in winter.

Conifers make good winter windbreaks

• Preventing erosion. Leaves catch falling rain and funnel it toward the tree’s trunk, dispelling energy so that soil is not displaced. Leaf litter and roots keep soil in place.

• Making their own fertilizer. Pollen, dust, bird and insect droppings, bacteria and fungi collect on leaves and fall to the ground with rain, carrying plant nutrients and also organisms that will help break down organic matter in soil into forms roots can use.

Trees build soil

Our predecessors knew that trees enhance city life. By continuing to plant trees along our streets, we can maintain that environmental benefit.

Milkweed's evil twin

I'll be selling gardeners' gift baskets at the farmer's market in West Newton, MA 9:30-12:30 on June 23, June 30, and every other Saturday thereafter until October 6. Stop by and say hello if you're in the neighborhood! The market is on Elm Street between Washington Street and Border Street.

Recognizing nonnative invasive plants can be discouraging. There are so many thriving along sidewalks, in parks, and on conservation land that it’s easy to feel that it’s too late. There’s no way to weed them all out. We have to pick our battles.

Japanese knotweed (Fallopia japonica) taking over a local parkway

    One manageable thing we can do in our own gardens is to keep an eye out for black swallow-wort (Cynanchum louiseae). 

A tangle of black swallow-wort vines

This vine is popping up all over my neighborhood. The reason it’s a problem, other than its swarming over shrubs and shading them out, is that it fools monarch butterflies. 

Monarch on a real common milkweed (Asclepias syriaca)

Females confuse it with native milkweeds, to which it’s related, and lay their eggs on the impostor plant, thinking it will provide food for their larvae. When the caterpillars hatch, they can’t live on black swallow-wort leaves, and they don’t survive.

    The first black swallow-wort vine I noticed in my yard grew up from the base of a particularly thorny rose bush and twined around the canes like a morning glory. I didn’t spot it until it was 3 feet tall. I never was able to uproot that plant. I couldn’t dig deeply without risking killing the rose. 

A hard place to dig

When I grabbed the base of the vine’s stem and tried to yank the roots out, it snapped at soil level. I keep working at it every year, watching for new tendrils as they appear in spring and pulling out as much of the plant as I can. Some year, I hope, it will run out of energy and die.

    Fortunately, that’s good enough to protect monarchs. Here’s a link to a helpful guide published by Newton Conservators, a local environmental group. As they explain, it’s useful to cut the plant to the ground. Later in the season, you can even help by cutting off the seed pods and throwing them in the trash to keep browsing animals from eating the fruits and then excreting the seeds to germinate somewhere else. Like other parts of invasive plants, the pods should go into the trash, not the compost or even the yard waste. They have awe-inspiring reproductive powers.

Butterfly weed (Asclepias tuberosa) is another milkweed relative and does support monarchs

    Down the block, black swallow-wort has overwhelmed a privet hedge that grows thinly because of the shade of a sugar maple. A net of vines drapes over the low hedge, hiding it completely. That means many seeds will be ready to spread around the neighborhood by the end of the summer.

    With that kind of population pressure, I can’t expect to keep black-swallow-wort out of my yard. I’ll just have to watch for it as I deadhead, prune, and weed. If I catch the sprouts when they’re small, I have a chance to keep them from taking over.

    Newton Conservators and other groups regularly mobilize teams to pull invasives on conservation land. Will this work have to be repeated every year to keep the culprits from growing back? Let’s hope volunteers replace the unwanted plants with native species vigorous enough to hold the ground.

Swamp milkweed (Asclepias incarnata), left,
or common milkweed (Asclepias syriaca), 
right, could be good replacements for black
swallow-wort

 

The little squirrels that could

I'll be selling gardeners' gift baskets at the farmer's market in West Newton, MA 10-2 on June 23, June 30, and every other Saturday thereafter until October 6. Stop by and say hello if you're in the neighborhood! The market is on Elm Street between Washington Street and Webster Street. 
 
Baby needs acorns—that seems to be the imperative for squirrels in my yard at this time of year. Local squirrels are in high gear, digging everywhere. 

Squirrels are persistent in their search for food. They've got all day.

I wake in the morning to find holes dug every six inches in the wood chip paths. There are few edible seeds or nuts around at this season. Squirrels are digging for food wherever soil is loose.

Wood chip paths make for easy digging

    Whatever I plant in the ground is in danger of being thrown back out by foraging squirrels. This year’s plan to grow vegetables and berries in containers on the deck is in serious jeopardy unless I can keep squirrels out of the pots until the plants are firmly rooted.

      Checking Google, I learn that other people are having the same problem. 

Can you see where squirrels dug a hole in the bottom right corner of this pot?

Writers promoting “natural” gardening recommend non-toxic repellents: human hair or dog hair, cayenne pepper, or bone meal spread on the soil surface. Folk remedies like these get passed on from gardener to gardener, but I’ve never found they had much effect on wildlife.

    Instead, I’m opting for mechanical barriers. One recommendation that recurred in my Internet search was to lay down chicken wire or wire mesh fencing and plant through it. Cutting a hole with wire clippers every time you plant a seedling sounds to me like a recipe for frustration and laceration. 

    I prefer to cover rows of seeds with row cover, a spun-bonded synthetic textile. I keep the fabric off the ground with rectangles of wire fencing with 2-inch openings. These are held down with small stakes. 

Peas under row cover

 I take the row cover off when the seeds sprout. I can remove the fencing when the seedlings have several leaves or let it remain to deter digging all summer. 

    I have to admit that this approach adds extra time and work to the job of starting the vegetable garden in spring. It does increase the chance that squirrels will leave the seedlings in peace.

    Protecting young plants in pots is even more complicated. This spring I’ve potted strawberry plants, a blueberry bush, a patio tomato, a bush cucumber, and two eggplant seedlings. I’ve planted radish and lettuce seeds in shallow containers. The question is how to keep these plants safe, short of standing guard all day. Past experience warns that they have little chance of surviving or producing without a barrier to keep squirrels out.

    I covered the little blueberry bush with a chicken wire cloche I bought from Gardeners Supply. 

Chicken wire cloche: adorable but pricey

Glass cloches were originally invented as mini-greenhouses, providing a warm, moist environment to encourage individual plants to grow. This one is just a barrier to keep marauders out. It’s not cheap at $25 plus shipping, otherwise I’d purchase a fleet of them. 
   
    After squirrels started digging in the other containers, I covered the pots with window screen or wire mesh or laid cut pieces of these around the plants on the soil surface, holding them down with small stakes or tomato cages. Still the squirrels find ways around my barriers. They never give up!

A squirrel found a way past the protective screening and threw mulch out of this tomato's pot

To cram or not to cram

My new perennial bed is approaching its first birthday, and I’m taking the opportunity to assess how it’s doing. Just about all of the plants made it through the winter, probably because the project was blessed with adequate rainfall in fall and spring and good snow cover during the winter. 

Bulking up for summer

I’d like to believe that letting a thick layer of whole leaves lie on the bed through the winter also helped the young plants.

    Now I’m seeing flowers on the new perennials and low shrubs. A yellow shrub rose (‘Kolorscape Yellow Fizz’) is blooming, 

and blue-eyed grass (Sisyrinchium angustifolium ‘Lucerne’)is covered with purple flowers.

Yarrow (Achillea ‘Coronation Gold’) is covered with buds that are about to open. One of the things I love about this new bed is its relatively sunny exposure. There are few spots in the yard that get as much sun as this area right off the back deck. I was able to choose species that need direct sun for at least part of the day, and they’re getting enough sun to flower generously.

    I tried to restrain myself from planting this new bed too densely. In the past, I’ve often crammed in so many plants that they suffered from lack of space. The more aggressive growers tended to take over, shading out the timid or out-competing them for root space and access to water. That’s one way I learned what will grow in my yard and what won’t. What’s here now is what survived.

    Over-crowding is hard to resist, because there are so many plants I’d like to grow and only limited space to put them in. This time, though, I tried to think about the mature size of the plants as I placed them in the bed. As a result, they’re currently surrounded by lots of open space. They should fill in by their third summer.

More mulch than foliage this May

    Thomas Rainer and Claudia West, on the cutting edge of landscape design, advocate a different approach to plant spacing in their book Planting in a Post-Wild World. They argue for cultivated landscapes that evoke archetypal natural plant communities, such as grasslands, shrublands and forests. Instead of making the soil and site hospitable to a list of favored plants, they match plants to existing site conditions.

    There are no open mulched areas between plants under their scheme, and there's no bare soil. Their herbaceous layer, which features perennials and grasses, is surrounded by low, spreading species that fill in all the gaps, both above ground and in the root zone. By allowing each type of plant its niche, they achieve a landscape as dense as a patch of weeds. Some plant uses every inch of soil.

All niches are filled as this lawn returns to nature

    As it happens, I did choose some low-growing native species for my bed: bearberry (Arctostaphylos uva-ursi), American cranberry (Vaccinium macrocarpon), and three-leaved stonecrop (Sedum ternatum ‘Larinem Park’).  

Who knew cranberry plants were so pretty?

I’m watching to see which will grow best. Perhaps they’ll weave themselves into the kind of tapestry Rainer and West describe.

Bearberry reaching out to surround taller perennials

 

A shared garden

Permaculture is a philosophy that inspires me, although I don’t anticipate fully realizing its ideals in my garden. It envisions a lightly managed landscape that provides for all living things, including humans.

Permaculture gardens combine many kinds of plants in a productive whole

 

     Reading Toby Hemenway’s book Gaia’s Garden, my introduction to this approach, I wondered about his suggestion that a home gardener grow multiple fruit trees as members in “guilds,” communities of plants that work together. What if I really had productive apple, pear, peach and cherry trees in my yard? I imagined I’d have far more fruit than my family could possibly eat. Composting fruit we couldn’t eat or letting it rot on the ground didn’t sound desirable or sustainable. 

Why grow more apples than you and passing raccoons can use?

    In a chapter on urban permaculture, Hemenway proposed viewing a whole neighborhood as a permaculture garden. I could grow an apple tree, another neighbor a pear, and we could share the fruit. That sounded more neighborly and much more practical. 

    When I’m walking around town coveting the flowering trees and shrubs growing in other yards, I’m reminded of Hemenway’s idea. We share the spring landscape. We all get to enjoy trees covered with sublime blooms. They’re a community asset, even if each tree grows in someone’s front yard.

Someone else's azaleas

    I don’t own a flowering dogwood (Cornus florida), which is one of my favorite native trees. I didn’t plant one when I started my garden because I thought they were all going to succumb to anthracnose, a fungal disease on the rise at the time. As we know, that didn’t happen. I can’t see where I’d shoehorn this understory tree into my landscape at this point. That’s OK, though, because so many beautiful white- and pink-blooming dogwoods grow in my neighborhood. 

Dogwoods are blooming in my neighborhood now

    I also don’t need to own pink lady’s slippers (Cypripedium acaule). These shy native orchids bloom at this time of year on woodsy hillsides with high shade from conifers. 

I came upon these lady's slippers during a walk in the woods

You can buy ethically grown specimens propagated in nurseries from seed (not plants collected from the wild, which is illegal on federal lands and undesirable anywhere else). But why take the risk? I don’t want to bring home a precious plant and kill it with the wrong growing conditions. Better to enjoy it where it grows naturally in local conservation areas.

    Oriental poppies (Papaver orientale) are among the beautiful perennials that are never going to grow in my yard. 

Oriental poppies don't work in my garden

I tried a few, but I just couldn’t offer them the right site. There was nowhere sunny enough in my yard. The one or two flowers they produced leaned hard toward the western light coming over the back fence, hiding their faces from our view. But I know of a front yard a few blocks away where a talented gardener displays a luscious swath of these flowers every June. All I have to do is stroll by this neighborhood asset.

    I remind myself that I don’t have to own one of every plant I admire. I can enjoy them in the larger garden that we share.

More irises than will ever bloom for me, in a neighbor's yard

 

If all you have is a hammer, everything looks like a nail

Why are landscape contractors so attached to work they can do with machines? A recent conversation with a fellow gardener reminded me of this frustration. Her lawn service uses a weed wacker—a string trimmer—to cut back weeds in her yard instead of uprooting them. 

A string trimmer shortens weeds but doesn't remove them

As I pictured it, they’re leaving the weed plants a couple of inches tall. From the weeds’ point of view, this is helpful pruning. They marshal their underground resources and send up more growth. She finds the weeds are spreading. The crew leaves her property looking neat, but they’re not serving her gardening purposes.

    I have the same experience, and it’s getting more acute as I shift toward my version of sustainable gardening. I employ a landscape contracting company that I’ve known for years. I know that the leadership of the company includes several people with strong horticultural knowledge. The actual mowing, though, is done by a team of two or three young men with many stops on their schedule for the day and little time for tailoring their approach to suit my wishes.

Can I buy lawn care that's consistent with my sustainable approach?

    Last time they visited, I happened to be out in the garden. The team leader stood next to my new perennial bed, painstakingly mulched with shredded leaves, and asked whether I wanted them to use the leaf blower. He remembered that I’d said no to leaf blowers in the past, for which I’m grateful. But I had a strong feeling that if I hadn’t been at home, my leaf mulch would have been blown off the bed in a few seconds, and I’d have been stuck buying bark mulch from the garden center.

I put that leaf mulch down on purpose

    That would have wiped out all my efforts to mulch with materials I find near home, minimize carbon cost, and maintain habitat for native insects.

    I’ve talked with the supervisor of the team at least annually about how I want to maintain the garden. I’ve put up signs asking the men not to remove fallen leaves from the property. Things have improved, but there are regular relapses. My approach just doesn’t seem to compute for them.

    Another sore spot is grass clippings. It took effort to get across the message that I don’t want them removed from my yard. That’s organic material that should stay here and build soil. I ask to let the clippings lie on the lawn. 

Instead of moving clippings to the compost bin, you can let them compost in place on the lawn-photo anneheathen

Yet each spring I’ve had to call and beg for this request to be honored. It’s not the way the team is used to doing things, and it probably looks messy to them.

    It may be more efficient for landscape contractors to do the same work in every yard and to work with power tools—gas powered mowers, leaf blowers and string trimmers--despite the dust and exhaust the operators inhale and the hearing loss they incur from the noise. But we customers are paying for this one-size-fits-all service. It’s time for us to vote with our pocketbooks and seek out contractors who are equipped to accommodate a more plant-friendly and environmentally conscious approach.

Pushing up through the leaf mulch