Groundcover throwdown

Last fall I wrote about uprooting smooth Solomon’s seal (Polygonatum biflorum) under a crabapple that occupies a very visible spot in our landscape. This native plant has spread widely in my yard. I brought home three as a groundcover for shade, and now 25 years later, their descendants are taking over every shady spot in the yard. They may be beneficiaries of our sprinkler irrigation system, which keeps the soil from drying out in the summer, unintentionally catering to smooth Solomon’s seal’s preference.

Smooth Solomon's seal shows up in every shady spot

    This spring I wasn’t surprised to see new shoots of the plant emerging in the section I’d tried to clear last year. It’s hard to remove every scrap of the white rhizomes. What’s needed, I realized, was something to compete with smooth Solomon’s seal. I should choose a shade-loving plant that would be tough enough to hold its ground, but not so aggressive that it would become a problem. Easier said than done. Smooth Solomon’s seal, along with some other unfortunate choices, has taught me that plants can take years to reach a critical population mass that enables a bid for hegemony.

Will fragrant Solomon's seal also turn into a thug? Time will tell

    To avoid bringing home neonicotinoid-treated plants, I’ve learned to look around the garden for things to transplant before heading out to the garden center. I could certainly move some Canadian wild ginger (Asarum canadense) to the area under the crabapple. Its round matte leaves stay clean and fresh-looking through the season. There’s already a lot of it in the yard, though, and its foliage is quite similar to that of bloodroot (Sanguinaria canadensis), which is already growing along the path that delineates the bed. I was hoping for a new look.

What can succeed in territory temporarily cleared of smooth Solomon's seal?

    European ginger (Asarum europaeum), another in the same genus, might also work. While smooth Solomon’s seal claimed territory in the yard over the years, clumps of European ginger have slowly expanded, and now new volunteers are popping up and forming colonies on their own, a sign that the species is finally feeling at home in the garden. I love its shiny round leaves with their subtle pattern of lighter-colored veins. I can dig some clumps from a bed along the driveway to try their luck under the crabapple.

European ginger making itself at home next to the garage

    At the Massachusetts Horticultural Society’s Garden Fair last weekend, I spotted an interesting option, Carex siderosticha ‘Snow Cap,’ with leaves that are almost all white. 

Easy to see why this broad-leaved sedge was named 'Snow Cap'

The volunteer who sold it to me warned that it needs lots of shade, and that’s exactly what it’ll get under the crabapple. With no competition, this rhizomatous, creeping sedge might make a bid for world domination. Let’s hope the energy it expends holding back smooth Solomon’s seal will keep it in check. With so little green leaf surface, it can’t be a photosynthetic powerhouse.

    I’m planning to start with those two and any wandering bloodroot seedlings that I can find and transplant. It’ll be interesting to see what happens under the crabapple once these plants go in. I suspect a guide and referee may be needed.

European ginger and bloodroot coexisting elbow to elbow

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

   

Beware of Greeks bearing gifts

One of my biggest gardening mistakes was planting smooth Solomon’s seal (Polygonatum biflorum). This seemingly modest woodland plant aims for world domination. Now I’m trying to beat back its onslaught.

Smooth Solomon's seal emerges in spring

    I first encountered smooth Solomon's seal in the shade plant section of my favorite garden center. At the time I was coming to grips with the fact that I was gardening in shade. I was delighted to discover lots of plants with pretty foliage in a shady corner at the far side of the sales area. Smooth Solomon’s seal caught my eye because of its arching stems, shiny leaves, and pendant cream-colored flowers. 

Seemed like an understated, elegant woodland plant--photo Peter Gorman

I didn’t seek out native plants at that time, but since it was a North American native, that must mean it wouldn’t run wild, right?

    For several years I thought I’d picked an excellent plant for shady areas where nothing else wanted to grow. About ten years in, though, I noticed that smooth Solomon’s seal was showing up in every shady part of the yard—and that’s most of my garden. Its little blue fruits must have been making their way to new territory. In retrospect, I might have been safer with an attractive Eurasian cousin, fragrant Solomon's seal (Polygonatum odoratum ‘Variegatum’), which has a pretty chartreuse border around its leaves and seems to be less spreading—so far.

A more sedate Solomon's seal? Or crouching to spring

    It’s not too hard to dig out smooth Solomon’s seal. When you do, one reason for its success in dry soil becomes obvious. It has big fleshy rhizomes, underground storage organs that look capable of storing plenty of water and nutrients. 

Rhizomes store supplies for hard times

I’ve learned not to throw these or the blue fruits on the compost pile, because both produce new plants. Moving compost around, I may have unknowingly carried them to new areas of the yard. 

Fertile fruits of smooth Solomon's seal

Instead I now send them out as yard waste, to be cooked at weed-killing high temperatures at the municipal composting site.

    There’s a crabapple tree that I look at every day from our kitchen windows. I’d sure like to grow other shady woodland flowers under it, not just smooth Solomon’s seal. 

A pot of elephant ears attempts to disguise rampant smooth Solomon's seal under the crabapple

What holds me back from ripping it all out is the fear that I’ll kill the tree in the process. I once read a sad story about a man who killed a beloved dogwood by digging among its roots to surround it with daffodil bulbs, and I think I executed a venerable Japanese andromeda (Pieris japonica) when I pounded plastic edging through its root zone.

     So I’m removing the unwanted smooth Solomon’s seal cautiously, bit by bit. Last spring I dug out a wedge-shaped patch of it from the tree trunk to the drip line. This fall I did the same in a slightly larger wedge, arguing that the tree was ready for this because of our wet summer. Time will tell whether I went too far.

A section cleared of smooth Solomon's seal-- for now

    The main remedy will be to plant something else that can stand up for itself in place of the plants I tore out. Smooth Solomon’s seal abhors a vacuum.

Attention friends: I'll be speaking at the Massachusetts Horticultural Society's Ecological Gardening Symposium on November 8 at Elm Bank in Wellesley, MA. Here's a link to the program information. I'd love to see you there.