An attractive menace

On July 14, I wrote about doubting I could keep my potentially invasive silk tree (Albizia julibrissin, also known in the US as mimosa) from spreading. Now that looks even more unlikely.

    With last weekend’s snowfall mostly melted, I notice many silk tree seed pods lying on the grass. Some are empty, and some still contain their brown seeds.

    Silk tree is a native of Asia that was imported to North America in 1745. It's a pretty tree with delicate, feathery foliage that makes pink puffs of flowers in July in my yard. 

This is a photo from Texas. Mine don't flower this densely

Silk tree spreads especially in disturbed ground and is now invasive in the southeast US. It has a number of characteristics that enable invasiveness: it produces a lot of seeds, it’s a legume, so it can extract nitrogen from low-nutrient soil, and if reproducing by seeds fails, it can also spread vegetatively from root fragments. 

     Its seeds require scarification (breaking through the seed coat mechanically, chemically or with heat or cold) to sprout and without this can stay dormant for many years before germinating, which allows them to seize growth opportunities when they arise. The seeds are efficiently dispersed, initially by gravity, secondarily by wind, water and animals. 

    That may explain why I’m finding the pods farther and farther from the tree, some at least 50 yards away on the other side of the house. More ominously, I see some have left our property and made it to neighbors’ lawns. I’ve found clusters near tree trunks, so it may be that squirrels or birds are carrying the pods away to eat the seeds and are dropping pods on the ground under the branches. 

    In this weekend’s thaw I’m picking up as many of the pods as I can and throwing them in the trash—I won’t compost them, because that would probably just distribute viable seeds wherever I spread compost. 

     I’ll be sorry to lose this pretty tree, but next spring I think I’ll have to cut it down.

Beautiful but damned

 

Littering, dog poop, and the climate change accord

With snow making gardening a memory and a hope, I want to write this week about a larger environmental topic. I’ll start at ground level.
     One of the great questions that has haunted me all my life is why people litter. What are you thinking when you go to a conservation area for a walk in the woods and drop your soda can or lottery ticket beside the path?  

Now it strikes me that littering has something to tell us about addressing climate change.
     I’m a dog owner, so I find behavior around dog poop particularly puzzling and frustrating. A significant minority of owners bags the dog waste and then leaves bags along the path or sidewalk. They may intend to come back and retrieve the bags at the end of the walk, but I can testify that many of those bags get left behind. 

     Psychologist Robert Cialdini and colleagues actually researched determinants of littering in 1990. In a 2014 Atlantic interview, Cialdini asked a better question than mine: why don’t people litter? “The crucial question is why don’t they litter, since the easy thing is to litter . . . Their attitudes toward the environment make a difference, but what they perceive as the norm is key.”
      As we ask ourselves how to translate the climate change accord’s commitments into action, we could take a lesson from Cialdini’s research. By presenting cues suggesting that littering is socially unacceptable, his group was able to make people in a library parking lot less likely to drop a handbill left on their windshields to the ground.
      Maybe those dog owners I criticize are getting cues from their dog-walking circle that dropping poop bags on the ground is the norm. In my friend group, driving a hybrid car allows me to pat myself on the back for being part of the solution. I was happy with that until someone pointed out what a tiny step it was on the road to sustainability.
      An adjustment of norms could help rein in the ultimate form of litter, carbon emissions. The conference delegates in Paris seem to have had something like that in mind when they set up the transparency aspect of the agreement, requiring governments to report back on emissions reductions. A California utility company has already demonstrated success nudging homeowners to reduce electricity use by comparing their use to neighbors’. No one wants to be the loser in a competition.
      We’re going to need systemic changes that make it the norm—easier and more consistent with our self-image--to conserve energy and switch to renewable sources than to stick to our old ways. Asking nations, communities, and individuals to do what’s harder and more expensive because it’s right can only get us so far. Systems have to change so that people can. We’re ready to do our part, but without that bag conveniently at hand and the trash barrel at the park gate, we’re likely to leave the dog poop on the ground—and drive off in that Prius. 

 

For the birds

     I heard a wonderful talk last week by Claudia Thompson, founder and president of Grow Native Massachusetts. Claudia spoke at a meeting of the Temple Shalom Garden Club in Newton.

    Claudia’s topic was the importance of growing native plants in home gardens. She illustrated how she created a lovely native plant garden in her yard in Cambridge.

    By planting native trees, shrubs and perennials, Claudia created habitat for many native animals, from soil organisms to insects to an amazing number of bird species. Photos from her yard captured birds I never expected would frequent a city garden.

    After hearing Claudia’s talk, I’m fired with enthusiasm to provide habitat for native birds in my own yard. I walked around the garden considering what I’d done for the birds and what else I could be doing.

    Claudia listed basic bird needs: food, in the form of insects, seeds and fruits, water, shelter, and cover for nesting and foraging (more information is available on the group’s website, www.grownativemass.org). She provides all of these necessities in a small garden, for example she attracts flocks of beautiful cedar waxwings who feast on the spring fruit of a grove of amelanchier, a small tree commonly known as serviceberry, juneberry, shadblow or shadbush. I’ve seen cedar waxwings farther north in the Adirondacks, never in my garden.    

      Looking at my own yard through the lens of Claudia’s talk, I recognized that I do have trees and shrubs of varying heights, including evergreens, that allow birds to flit safely from perch to perch. Two birdbaths are located near cover so that birds can feel safe. 

Birdbath beneath a thistle seed feeder

I’ve got quite a few native plants that provide food for birds, from towering conifers to low-growing native perennials. I even have two amelanchiers that produce the garden’s first tree fruit of the year in June.
  

     A knowledgeable birder, Claudia recognizes the call of the cedar waxwings when they arrive to check out her trees. I can’t identify them by ear, and I don’t spend enough time in that corner of the garden to spot them if they did come. The amelanchier berries disappear quickly. It’s possible that flocks of hungry waxwings are swooping in undetected. That’s not a completely satisfying thought. I wish I’d planted the trees within view of the house, as Claudia did.

      An area where I need improvement is my leaf litter management. Claudia reported that fall leaves lying on the ground, which I’ve been chopping in my leaf shredder for mulch, harbor insects and snails that play important roles in the garden ecosystem, including providing food for birds. She recommended letting the leaves alone to decompose in place.

      Whole leaves blow around, and in front of the house that’s a problem for my neighbors, who work to keep their lawns leaf-free in winter. To meet the neighborhood standard, I’ll need to keep raking and chopping leaves that drop in the front yard.

Leaves blow around if left on ground cover beds in front of the house

In back, though, I’m convinced I should try Claudia’s system, raking leaves off the lawn but letting them lie unchopped on the beds, even near the house.

Coral bells (Heuchera 'Montrose Ruby') under fallen leaves this winter

Then I want to find out more about native plant communities—and learn some bird calls.

Sun rays for winter days

Have you read Frederick, a picture book by Leo Lionni? Frederick is a mouse poet who doesn’t join in when his mouse compatriots are harvesting seeds in summer to eat during the winter. 

     He tells them, “I gather sun rays for the cold dark winter days.” He stores up impressions of the warm months. The other mice think he’s a slacker, but when the bleak winter comes, they are sustained by his stories as they huddle inside a stone wall.

    I find myself thinking about Frederick at this time of year. I too have wanted to store sun rays to get me through the winter, to buoy my spirits and also to make things grow next spring. 

Paperwhite narcissi bring some stored solar energy indoors in January

     The sun’s rays are embodied in the basic components of my gardening activity. The brown leaves and needles lying on the ground now, the gray trunks and branches of trees and shrubs, all represent the sun’s energy, captured through photosynthesis and stored in plant tissue. 

    In aiming to garden sustainably, I’m trying to keep that stored energy in my yard instead of sending it away. That’s why I ask the lawn service to let clippings lie on the grass to compost in place. It’s why I chop fallen leaves and use them as mulch. Both add organic material to the soil, which means keeping solar energy here where plants and animals can use it. As one of the resident animals, I want that energy to go toward growing garden plants I love.

    It would be even better if I could keep twigs and branches from trees and shrubs in the yard to make compost, mulch, or brush piles to shelter wildlife. So far I haven’t found ways to do that. Oak branches would take decades to decompose unless I chopped them into chips, which I’m not able to do. On a third of an acre lot, I begrudge space for a brush pile.
    
     My “sustainable-enough” approach has been instead to send out woody prunings to the city’s composting operation with the yard waste and use wood chips kindly delivered by a local arborist, Kevin Newman, for mulch.  This exchange means that the mulch doesn’t originate on my land, but it doesn’t incur much carbon cost for travel—the chips are from nearby trees. 
 

     It was nice to learn that trees aren’t totally locked in suspended animation during the winter months. They’re dormant, with slowed metabolism, but they’re poised to take up water when soil temperatures are favorable, between approximately 32 and 41 degrees.

This white pine appreciates snow cover

    A consistent insulating layer of snow can keep the soil in this temperature range. The snow allows evergreens to keep their needles from drying out and enables all trees to send out new roots in early spring by holding a little of the sun’s warmth in the soil.  Sort of like Frederick’s stories.

Return of the repressed

Happy New Year! My resolution for 2016 is to learn more ways to keep unwanted insects in check. In 2010 I told my pest control company to stop spraying my shrubs with pyrethroid pesticides for leaf damage that was only cosmetic. Now the results of this decision are coming to light, and I need some tools other than pesticides to deal with resurgent pests.

    It’s not something I’m proud of, but over the years between 1996 and 2010 I accumulated a schedule of pesticide applications to combat such insects as lace bugs and black vine weevils. True, the insecticides used, cyfluthrin and deltamethrin, are synthetic analogs of pyrethrum, an extract of chrysanthemum flowers. They’re relatively non-toxic and quickly broken down. Nonetheless I decided that to consider my gardening sustainable enough, I’d have to lose these pesticides.

    At first I congratulated myself on having stopped unnecessary spraying. I didn’t notice any new damage. It looked as if there would be no problem.

Lace bug damage on andromeda leaves

     This fall, after the busy gardening season subsided, I started to see telltale signs. The leaves of a prized Japanese andromeda (Pieris japonica) that’s very visible at the front of the house showed speckles betraying the return of lace bugs. 

Lace bugs are named for their lacy markings

The adult lace bugs and the immature form, the nymphs, both suck juices from leaves of their chosen plant hosts.  

    Next, when I was raking leaves, I saw something I’d never observed before: notches chewed out of the leaves of a large Catawba rhododendron (Rhododendron catawbiense).

Notches chewed by black vine weevils

This is the calling card of the black vine weevil. The grubs that are the weevils' larvae are more damaging than the adults, because they feed on roots and lower stems. 

The culprit

This shrub too plays an important role in my garden design. It’s about the size of a VW beetle, and it’s right in the foreground of the view from the windows at the back of the house.

This rhododendron was here when we moved in 30 years ago

    I took a deep breath and reminded myself that none of these insects was likely to kill the shrubs they were chewing on. And going back to spraying is not my only alternative. Because I used to rely on pesticides, I’ve never explored other methods of control. 

    I’m starting to collect some approaches used by organic gardeners. Next spring I could spray plain water to knock lace bug nymphs off my andromeda. I could surround rhododendron trunks with burlap or hang sticky traps to collect adult black vine weevils at night. I hope to add more non-chemical methods to this list.

    In 2016 I’m also not going to try to eliminate problematic insects completely. If I want a balanced insect population, I’ll need to have insect prey around for predators such as parasitic wasps to eat. Otherwise they won’t visit my yard. The goal will be to set acceptable levels of plant damage and let each insect contribute its part in the food web.