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