Corralling climbers

As a garden fills up at ground level, it’s tempting to go for vertical growing space by adding vines. I’ve done my share of this in recent years. I’ve learned that their vitality and vaulting ambition can be either a boon or a disaster.

Honeysuckle can be a pleasure or a monster, depending on conditions

    Take hardy kiwi (Actinidia arguta). I’d received a specimen of its variegated cousin, Actinidia kolomikta, as a membership bonus from the Arnold Arboretum.

Variegated hardy kiwi-photo David J. Stang

It grew moderately where I planted it against a north-facing wall along the driveway. I thought another member of the genus would be similarly docile, and I ordered male and female seedlings so that hardy kiwi could produce grape-sized kiwi fruit.

'Weiki' hardy kiwi

 
     Too bad I didn’t investigate the vines’ growth habits, because both hardy kiwis grew far too vigorously for my purposes. They quickly grabbed low-hanging spruce branches, and they looked ready to conquer the 40-foot spruce within a season. In the wilds of East Asia, they can reach 100 feet by scaling tall trees.

Hardy kiwi reaching for the sky-Jo Zimny photos

    My climbing hydrangea (Hydrangea petiolaris) is the apple of my eye. But it too was a lot more ambitious than I expected. In its first 10 years, the vine got a firm hold on an adjacent oak. It began producing its romantic clouds of white flowers in June. 

Climbing hydrangea in bloom

Instead of twining like the kiwis, climbing hydrangea attaches to its supports with adhesive disks called holdfasts. While covering more of the trunk every year with flowers, it’s also formed a mat on the metal garage roof, creating a microenvironment where Oriental bittersweet (Celastrus orbiculatus), a nonnative invasive vine, has found a foothold. 

At 20 years, the climbing hydrangea has taken over the garage as well as the oak trunk

     Birds must have dropped bittersweet seeds on the roof, and now bittersweet wands are reaching for oak branches. 

Bittersweet berries attract birds, as well as makers of holiday centerpieces

These strangling vines really could kill the tree. I think the only definitive solution will be to cut the hydrangea vine off the roof to eliminate the trap for leaf litter that incubates bittersweet seedlings.

    Less vigorous are the many varieties of clematis I’ve planted. Their flowers are so enticing that I can’t resist buying new ones. Clematis are reputed to prefer having their heads in the sun and their feet in the shade. I’ve found that they also need a minimum of competition and plenty of coddling. I’ve had best luck with an old-fashioned variety, Clematis ‘Jackmanii’. 

Clematis 'Jackmanii'-photo k yamada

It flowers reliably in a sunny spot along the driveway. More recently I’ve tried training clematis up trees and shrubs. They hold on by wrapping their petioles (leaf stalks) around twigs, so they don’t kill supporting plants. 

    As with so many plants in my yard, the controlling factor for my vines is how much sun they get. A clematis growing in sun on a tuteur in the insectary bed produces bounteous elegant blue flowers in May.

Clematis in its happy place

Other clematis vines grow lots of stems and foliage but not many flowers as they climb under the shade of supporting trees. Those too-shaded clematis may not flower profusely, but they don’t try to take over. It’s a delicate balance.

Would you like to see how the sausage is made? I'm offering a fall gardening course in my yard on Saturdays October 26 and November 2. You can sign up through Newton Community Education here.

Stalking invasives--in moderation

At this time of year, every morning there’s something new happening in the garden. This weekend daffodils and magnolia blossoms opened. 

 

Star magnolia and Magnolia 'Leonard Messel' popped into bloom overnight

Also burgeoning: invasive plants. These super-survivors start early and finish late, sprinting out of the starting blocks while competitors are still dormant.

My arch-nemesis, Norway maple, gets a jump on the season

    Before everything else leafs out, providing camouflage, it’s relatively easy to spot the nonnative problem plants. Now is also I time when I’m not dizzily spinning from task to task, as I will be in May.

    First on the list, I need to check on Japanese knotweed (Fallopia japonica) that’s surfaced along the south fence line. This could be the year I stick to my plan to foil this potentially powerful land grab. I’m sure you’ve seen Japanese knotweed, because it lines highway shoulders and any other areas where soil is disturbed and then left uncovered. 

Japanese knotweed seizes any open ground

Once it starts growing, it’s almost immortal. Like many invasives, it makes lots of seeds. The underground part of the plant is the real menace, though. To eradicate stands of Japanese knotweed, the Massachusetts Department of Transportation has to remove all soil down to 3 feet and burn it. That’s because if even a nubbin of root is left, the plant will grow back. My strategy for Japanese knotweed is to cut it to the ground every two weeks. Eventually if it can’t make energy through photosynthesis, it should dwindle and die. At least that’s the theory.

Last fall I tagged this sprig of Japanese knotweed so I won't miss it

    Garlic mustard (Alliaria petiolata) is another rapid spreader in our area. It’s easy to uproot. I need to catch it all before it flowers and sets seed in its second year, though, or it’ll take over. Garlic mustard emits allelopathic chemicals that suppress other species’ growth. This is one of the few invasive plants in North America that thrives in a shady forest habitat, such as what prevails in much of my yard.

Garlic mustard impersonating an early perennial

    When I pull or cut down these plants, I can’t throw them on the compost pile. If I did, I’d be spreading the unwanted plants whenever I distribute compost. It goes against the grain to bag invasives and throw them in the regular trash, but adding them to the yard waste would pass them on to someone else’s garden.

Volunteer pulling garlic mustard at Cuyahoga Valley National Park-photo NPS/Arrye Rosser

    Of course, officially recognized invasives aren’t the only plants growing aggressively in my garden. Lots of plants I chose myself, including native smooth Solomon’s seal (Polygonatum biflorum), have turned out to be thugs that I have to beat back every year.

Smooth Solomon's seal shooting up from the leaf litter this week

    I don’t like to get too hysterical about invasive plants. They’re mostly responding to human alterations of plant habitat, diving in to pioneer newly disturbed soil. The nonnative invasives in my yard didn’t parachute in from abroad, they just made it under the fence from adjoining properties where people are less interested in policing the landscape. Spending some gardening time keeping them at bay does seem worthwhile, though. The more garden space they claim, the less there’ll be for a diverse landscape that includes native plants.

With help, I hope native inkberry will grow instead of  Japanese knotweed

   

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