Choosing a successor

This fall I made a difficult decision to cut down two trees that framed the view from the house into the back of the yard. Now I have an opportunity to plant in the space left behind by a crab apple, Malus ‘Donald Wyman,’ that I picked out soon after we moved into the house in 1985. It stood next to our tallest tree, a towering red oak. As you’d predict, that oak proved to be its greatest challenge.

    The crab apple did bloom, more than I had a right to expect after planting it in part shade. It made lovely red buds that opened to white flowers with a delicate apple blossom scent. It produced small red fruits for the squirrels and birds. But over the years, reaching for the sun deformed its shape. Despite annual pruning efforts, it stretched its branches away from the oak. I couldn’t face another winter of being reproached by the misshapen leafless form of this tree.

 

Leaning redbud and twisted crab apple flank the path

    The other tree we cut down was a lovely white-flowering redbud, Cercis canadensis f. alba planted under a tall white pine. It had the same malady as the crab apple. Its shape as it reached for sunlight was uncomfortable to view.

    After a wrenching day when the two old friends were reduced to wood chips, I felt vindicated by the new vista. Instead of viewing the back of the yard through a small opening, we could now see all our trees and enjoy their contrasting textures. 

The new view, November

We’re left to decide what to plant in the open space where the crab apple used to stand.

 

The goose marks the empty spot

    There are numerous criteria. We want something that flowers in spring, so it needs to harmonize with the pink blooms of a nearby ornamental plum. I’d like to choose a New England native, or at least something that’ll be native here soon as the climate warms. I’m looking for a sizeable shrub or a multi-stemmed tree that I can prune myself, so it shouldn’t grow too tall. And it would be nice if it produced fruit to feed local wildlife. It’ll get morning sun but have to cope with the shade of the oak for the rest of the day. A lot of the native shrubs that appeal to me are happiest in a moist location, but they won’t get much moisture in the crab apple’s spot.

    Here are some ideas: 
•    Red and black chokeberry (Aronia arbutifolia or melanocarpa) produce small white flowers and attract birds with their red or black fruits

Red chokeberry 'Brilliantissima'

 
•    American cranberrybush (Viburnum trilobum) has elegant white flowers and red fruit in fall

American cranberrybush

•    Coastal serviceberry (Amelanchier obovalis) blooms early and attracts birds with its fruit

Coastal serviceberry

•    Red osier dogwood (Cornus sericea) has bright red stems that stand out in winter

Red osier dogwood

•    Pink shell and roseshell azalea (Rhododendron vaseyi or pinophylllum) have early pink flowers

Pink shell azalea

•    Pussy willow (Salix discolor) produces pollen when it’s most needed in early spring

Pussy willow-photo Thomas Kent

Which will it be? There’s a long winter ahead for considering the choice.

Fighting fire with fire

 One of the techniques I’m using to control invasive plants in the garden is planting vigorous growers, preferably natives, to claim their space. Invasives love disturbed ground. If I pull them out and leave the soil open to falling seeds or probing roots, I’ll have to do the same job over again. Rather than spending my gardening time fighting off invaders, I prefer to fill the garden with so many successful plants that invasives can’t find a foothold. At least that’s the theory.

    I’m trying this competitive approach to keep out Japanese knotweed (Polygonum cuspidatum). Wherever there’s a patch of bare soil, this highly successful nonnative forms tall thickets that crowd out native plant communities.

Japanese knotweed is the ultimate opportunist

     In my yard, Japanese knotweed pops up along the fence line every year, and I do my best to root it out. This will never be a permanent solution, because no one’s trying to eradicate it from the yards that abut mine. Rhizomes will keep spreading under the fence.
Knotweed multiplies by creating a thick, rapidly expanding mat of roots. If I cut the roots without removing the whole stand of knotweed, I’m actually stimulating more growth.

    This spring I decided to fight fire with fire. I planted a coralberry (Symphoricarpos orbiculatus) next to where knotweed keeps emerging along the back fence.

Coralberry-photo Severnjc

 

This native shrub is known as a suckering spreader. Most write-ups focus on how to keep it in check rather than how to coax it to grow. I’ll encourage coralberry to form a thicket to keep the knotweed from pushing its way into the yard. This summer the young coralberry is slowly expanding, despite being shaded by the fence and some giant pokeweeds (Phytolacca americana).

 

Coralberry guarded by tall pokeweeds

 
     Not all the aggressive growers that I need to beat back are state-certified nonnative invasive plants. Those are certainly a problem, but some of the too-vigorous plants in my yard are natives, such as smooth Solomon’s seal (Polygonatum biflorum). Native plants can range from shy to aggressive too, just like imported plants, as I learned the hard way.

Smooth Solomon's seal taking over

 
     I chose smooth Solomon’s seal because it was recommended for shade. Thirty years later, it’s taken over large areas in the shade of large trees and shrubs. It doesn’t do this in every garden; it’s just found growing conditions in my yard that suit it all too well.

      I’m making a start at reducing the smooth Solomon’s seal population by pulling out its thick storage roots and planting vigorous growers in their place. I’ve had modest success encouraging preexisting clumps of a less-aggressive European cousin, variegated Solomon’s seal (Polygonatum odoratum var. pluriflorum ‘Variegatum’), to take over where the native had been king.

This variegated version is a nice alternative to aggressive smooth Solomon's seal. I'm ignoring the lilies of the valley, also spreading aggressively.

 
     A spreading clump of pawpaw (Asimina triloba), a small native tree, is shading out some of the smooth Solomon’s seal, with the side benefit of producing delicious edible fruit. Under the pawpaw’s shade, smooth Solomon’s seal isn’t sending up so many new plants. Now how to keep the pawpaw from taking over?

The pawpaw is forming a growing patch, worth it for the fruit

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Rising from bare roots

The bare root plants I bought this spring are thriving beyond my wildest expectations! These are native perennials and a native shrub that I ordered from Prairie Moon Nursery in Minnesota. 

I'm hoping for false aster flowers like these from a bare root specimen-photo David J. Stang

When I put them into the ground in late April, the idea was that they would send up stems and leaves rapidly. 

    Bare root plants are harvested earlier in the season than plants that have already leafed out. I’d seen bare root roses that arrived looking like dead sticks transform themselves into flourishing bushes covered with flowers. I’d never seen this happen with perennials, though, and I wasn’t sure how many of them would make it.

Would this become a 3-by-3-foot flowering  plant?

    I wanted to try this approach because it would serve two environmental goals. Roots are smaller and lighter than perennials in full leaf sitting in pots of moist growing medium. 

A plant in a pot takes more energy to ship

That means they carry a lower carbon cost for shipping. In addition, I’ve been looking for ways to use less plastic. The bare root plants were shipped inside plastic bags, true, but that was much less plastic than what I’d be getting with potted plants. I was glad to see that the nursery bagged all plants of one species together, rather than wrapping them individually.

    The little roots seemed delicate when I opened the bags. The garden was just coming into leaf as I carefully nestled them into the soil I’d prepared for them. Then we had a cool May, and the ground stayed moist. That was lucky, because the leaves and pine needles I covered the bare root plants with to hide them from digging animals fooled me too. I often forgot to water them.

    Almost two months later, the bare root plants are definitely doing what they were supposed to. In the bed next to the deck, wild strawberries (Fragaria virginiana) 

Wild strawberry

and wild geranium (Geranium maculatum) popped right up through the chicken wire I’d laid over them for protection. They’re now robust young plants that look ready to face the summer. 

Wild geranium

I sited the early meadow rue (Thalictrum dioicum) next to a bird bath so it could catch some extra irrigation when I slosh out dirty water to replace it with clean. This plant sent up a half dozen slender wiry stems topped with small fern-like leaves. I hope to see its pale yellow flowers next spring. 

Early meadow rue

False aster (Boltonia asteroides) got a sunny spot next to the fish pond. 

False aster

It’s not taking off like a potted New England blazing star (Liatris novae-angliae) has nearby. It’s alive, though, and presumably gathering its strength for a growth spurt later in the summer.

New England blazing star

    Truly impressive is the bare root coralberry (Symphoricarpos orbiculatus) that I planted and mostly neglected on the slope leading down to the back fence. Left on its own, it sent out leaves and looks to be thriving. 

Coralberry

This shrub is reportedly a vigorous grower. I’m hoping that its somewhat adverse conditions in my yard will keep it to a reasonable size while it provides wildlife with welcome flowers and fruit.

Native plants spreading good cheer

As we enter June with everything blooming, I feel like putting aside serious garden subjects to drink in the garden’s exuberance. So I thought I’d check on some of the native plants I’ve added in the past couple of years and show you how they’re doing.

    This week I was thrilled to see my cross vine (Bignonia capreolata) burst out with its coral, orange, and yellow trumpet-shaped flowers against the garage. I was expecting it to need more time to recover from transplantation and our northern winter. But no, it’s on the move and offering lots of opportunities for pollinators already.

Cross vine is a vigorous grower

    Nearby, a trumpet honeysuckle (Lonicera sempervirens) is covered with flowers. It seems to bloom more generously every year, although its roots are in a dry patch under the house’s eaves and surrounded on three sides by bluestone pavers. The long narrow flowers are popular with hummingbirds as well as insect pollinators.

Trumpet honeysuckle: easy and gorgeous

    Among the native shrubs, Carolina allspice (Calycanthus floridus) is putting on an unexpectedly uninhibited show. I’d planted one in deep shade a few years ago. It flowers, but sparsely. A newcomer added last spring gets much more sun, and it’s responded accordingly. The weird dark red flowers are fascinating, and I know they’re drawing native insects to the yard.

Carolina allspice has distinctive flowers

    Next to it is a flame azalea (Rhododendron calendulaceum) that I moved from where it was languishing in the front yard, struggling to compete with the roots of the Norway maple towering in the curb strip. When I dug the azalea up, I found it had very little root mass, although it had been there for years. Now it’s got more room to expand in looser soil, and it’s already blooming despite the trauma of last year’s transplantation.

I hope this flame azalea will flourish in its new location

    In the same area, a volunteer black cherry tree (Prunus serotina) is growing by leaps and bounds. This spring it’s showing its first flowers. The challenge with this tree will be to keep it and its offspring from taking over, but I’m encouraging it because of its superior wildlife value.

Black cherry hosts many native insects

    Bearberry (Arctostaphylos uva-ursi) is technically a sub-shrub, although it’s only about an inch tall. I chose this woody plant as a groundcover in a new sunny bed in 2018. It didn’t do much for the first year, but now it’s expanding in all directions, sending out branching stems bearing shiny new leaves. I love seeing this plant growing wild on Cape Cod, and I hope it will spread out even more as a lovely background to taller perennials.

Bearberry likes sandy soil and sun

    In a shadier section of the same bed, a single young creeping phlox (Phlox stolonifera) has emerged and flowered. I recently saw creeping phlox recommended as a groundcover in a Boston Globe story about lawn alternatives. My goal is to see this bed carpeted with a tapestry of groundcovers, so that no mulch is showing. That won’t happen soon, but the creeping phlox’s survival is a good sign.

Creeping phlox getting ready to creep

    Why are these plants doing so well this year? I don’t know, but I’m glad.

Hopes for spring

Dear readers,

I hope you're well and bearing up as well as possible at home under the daily onslaught of coronavirus news. I’m going to keep writing about gardening, because I hope it can be a solace during this difficult time.

Glory of the snow is opening this week

    So, happy spring! In addition to starting a cutting garden and siting new native pollinator plants around the garden pond, I’m planning to shoehorn two new native flowering shrubs into the garden this spring: buttonbush (Cephalanthus occidentalis) and coralberry (Symphoricarpos orbiculatus).

    I’ve been wanting to try both of these shrubs for a while now. They keep showing up on lists of native plants valuable to wildlife. Buttonbush, according to the Missouri Botanical Garden’s Plant Finder app, has June flowers that are “very attractive to hummingbirds, butterflies, and other insect pollinators.” The common name comes from the globe-shaped flower heads, which are distinctive and adorable. Long styles extend from the petals, making the flower head look ready for space travel (The style is the stalk that connects a flower’s ovary to the stigma, the part that receives pollen; together the three make up the pistil).

Doesn't this buttonbush flower head look like it belongs on the Jetsons?-photo Jim Evans

    I got my little buttonbush from the plant swap run by our local plant conservation society, Native Plant Trust. Last September, when the Trust’s director of horticulture checked the offerings, he separated local ecotypes—native plants that grow naturally in our area—from North American natives from farther away. I was embarrassed to see that some of the perennials I’d contributed didn’t fit into this most desirable group.
   
    Even so, I got to take home some choice plants from other members’ gardens, including the 4-inch buttonbush in its little pot. It’s not showing any leaf buds yet, but buttonbush reportedly leafs out late in spring.

    If this buttonbush proves viable, I’ll need to plant it in relatively wet soil, which is scarce in my yard. The best spot would be the lowest lying area opposite the vegetable beds, where water pools when I drain the fish pond. Buttonbush needs at least part sun, so I’ll site it as far as possible from the shade of nearby evergreens. It can grow to 12 feet high. It may be a good choice for screening the recently installed chain-link fence.

A possible space for a buttonbush

    Coralberry, on the other hand, needs room to run. It’s described as a “dense, suckering” shrub that “spreads by runners to form impenetrable thickets in the wild” and does well in “open woodland areas where it can be allowed to spread.” 

Coralberry loaded with fruit-photo Severnjc

That sounds like the area in the back corner of the yard where we took down a big hemlock. There’s a steep slope down to the back fence where coralberry could have plenty of space. I’ve ordered a bareroot plant to set in this spring. 

Buying bareroot avoids the plastic pot-photo from Gardening Know How

I’m looking forward to seeing it covered with coral-red berries. If all goes well, that corner could be a bird paradise in a few years. By then, I hope I can invite guests over to see it.

Stay strong!
Becky

Do 'nativars' count as native plants?

For the purpose of supporting biodiversity in general and native insects in particular, do we have to grow only the straight species or “wild-type” of plants that grew in our region before European settlement? What about improved versions of those plants, referred to as cultivars or “nativars”? This turns out to be a complicated question.

    Unless you’re shopping at a dedicated native plant nursery, you’re likely to find few unimproved natives at the garden center. Most plants offered as natives will be cultivars that have been selected by horticulturists for desirable traits such as bigger, brighter flowers or unusual foliage color. You can spot a cultivar by a name in single quotes: for example, Echinacea purpurea ‘Sundown’ is a purple coneflower cultivar.

'Sundown' was selected for its petals' orange tint-photo Mike Peel

    Sometimes a spontaneous mutation occurs in a plant population. An observant nursery may notice the plant’s changed appearance and decide it has market value. Other cultivars are purposely created through many generations of breeding or even through genetic modification. Some are hybrids between two species. 

     Are nativars useful in pollinator gardens? It depends. Selection for horticultural use may change flower size, color, time of bloom, or foliage color. Any of these could confuse insects seeking pollen and nectar or could mean that bloom doesn’t occur when the insects need it. 

Pollinators have evolved to synchronize their life cycle with bloom times of flowers they need

Double flowers are often sterile, because in the breeding process, pollen-carrying stamens have been replaced by extra petals. These won’t offer visiting insects any reward at all.

Echinacea 'Razzmatazz' won't help pollinators

    In general, it seems that the more closely a flower resembles the straight native’s, the more popular it will be with insects. It’s an area of active research. Doug Tallamy and Emily Baisden have found that woody plants with purple, blue or red leaves are not useful to leaf-eating insects, probably because of the anthocyanins that give leaves their pleasing colors.

Heuchera 'Amethyst Mist' is pretty, but not attractive to leaf-eaters

      Annie White intensively studied pollinator visits to test gardens of native perennials and cultivars of the same species at the University of Vermont. Delaware's Mt. Cuba Center ran another perennial trial. 

Doug Tallamy and Emily Baisden vacuum up insects for study at Mt. Cuba Center

     In general, the unimproved native flowers attracted more insects, but some cultivars were also winners. A culvers root (Veronicastrum virginicum ‘Lavendelturm’ and a garden phlox (Phlox paniculata ‘Jeana’) were visited by more insects than their straight native counterparts. Researchers speculate that this is because the culvers root bloomed for longer than the straight species and the phlox had shallower flowers that made nectar easier to reach. Hybridization made flowers less useful to insects when it radically changed flower color or reduced production of pollen and nectar.

Small, shallow flowers of Phlox 'Jeana' make nectar access easy

    For gardeners who’d like to participate, three universities are running a citizen science project called Budburst that invites us to plant some flowers from a list and contribute scheduled, structured observations of their insect visitors.

    What can we take from the preliminary research? Generally straight natives seem to do the most for insects, but many nativars are useful too. We can encourage our garden centers to stock the unimproved natives. And plant breeders can help out by selecting and marketing flowers that benefit pollinators.

Farewell to a tree I loved to hate

I'll be presenting a free Green Newton lecture on Beautiful Sustainable Gardens at the Newton Free Library this Monday June 10 at 7:00 p.m. See you there! 

In April, I received a letter informing me that one of our two street trees was going to be cut down. I’ve been wanting to get rid of this tree for years. It was a Norway maple (Acer platanoides) that had been losing branches over the years, until all that was left was a large limb angling toward the house. 

 

The doomed Norway maple in May

     
     We’re on the side of the street with the power lines, so over the years the utility company has been hacking away at this tree and its partner at the other end of our street frontage. A few years ago, I asked the city to inspect the tree because I thought it was liable to drop a heavy branch on a pedestrian or a parked car. At that time, they found it was still sound. Now, the letter said, it had “significant defects.”
 

Marked to be cut down

     The reason I resented this tree wasn’t just its species. Yes, I dislike Norway maples for their fecundity and voracious shallow roots. This tree also cast dense shade over the front yard. It had limited what I could grow under its branches to the standard broadleaf evergreens you see everywhere in the neighborhood. A couple of years ago I added an oakleaf hydrangea (Hydrangea quercifolia) that livened things up a little, but still.

Ho hum boxwood, Japanese pieris, and mountain laurel

    One morning last week, two trucks arrived, and the urban forestry team took down the tree. I darted in and out of the house taking pictures to document the big event. 

Avoiding wires to saw off chunks

A bucket truck allowed a man with a chain saw to maneuver around the wires and cut the tree apart piece by piece. Another man operated a giant arm picking up large branches to haul back to the city yard for chipping. 

Future wood chip mulch

After half an hour, all that was left was the newly cut stump.

Its center was hollow

    I had six weeks to anticipate it, but this event caught me off balance. I wasn’t prepared to be sad to see the Norway maple go. Although I’d wanted it gone, seeing it chopped up so fast reminded me of how it had stood there patiently through blizzards, hurricanes, droughts, and nonnative insect attacks. The tree was misshapen at the end, but that comes to all who live to old age.

    The other surprise was my lack of ideas for what to add to that corner of the front yard. Without the tree’s shade, there are so many more options, including native shrubs I’d like to try. I’m not used to selecting plants for sunny spots. I’ve often thought that more highbush blueberries (Vaccinium corymbosum) should be grown in front yards. They have small neat leaves like privet (Ligustrum vulgare) that turn a pretty red in fall. 

Blueberry foliage turns red in fall

Unlike privet, though, they’re natives and not invasive. It would be a friendly gesture toward both birds and walkers to offer blueberries along the sidewalk.

Neighbors could pick blueberries as they passed

    When it’s too hot to work outside this summer, I’ll consider what else I could plant in the new sunny clearing this fall.