Just Say No to These Pass-along Plants
April 4th, 2023
This is the time of year when gardeners get outside to grapple with plants that are growing beyond their intended space – or growing where they aren’t wanted at all.
Here’s a patch of ribbon grass — a common pass-along plants — invading its way through a garden bed.
But since gardeners tend to be kind, benevolent, and nurturing souls, they often have a hard time digging and tossing these “surplus” plants.
It seems so hard-hearted!
And so lots of gardeners – dug-up rootballs in hand – go looking for foster parents for their newly homeless plants.
Sometimes these plants end up at plant sales, plant exchanges, and yard sales.
Unfortunately, many of these botanical castoffs are, to put it nicely, “overly frisky.” OK… they’re often weedy or invasive. In other words, people tend to dig and get rid of what’s turned out to be maintenance headaches.
Now that doesn’t mean you should run the other way when you see a neighbor heading your way with a mystery clump.
Sometimes pass-along plants turn out to be welcome gifts. If the culled-out plants aren’t invasive and match a site in your yard, this is a great way to fill or expand garden space at no cost. And the digger-outer feels like he/she has saved a plant’s life while doing a good deed for a friend.
My own gardens have been enriched over the years by gardening friends who gave me divisions of really nice plants.
I got a gorgeous velvet-purple bearded iris that way as well as a clump of betony ‘Hummelo,’ a long-blooming perennial that’s way under-used and at that time, hard to find in garden centers.
My first Polianthes tuberose – a tremendously fragrant white-blooming tender rhizome – also came via the freebie route.
On the other hand, before I knew any better, I once graciously accepted a division of variegated ribbon grass. Within three years, the clump was running around my perennial garden to the point where I had to dig everything up, unravel, and start over.
The trick, then, is sorting out the good stuff from the Trojan horses.
If you’re not familiar with an offered plant, ask the giver the key question of how much it spreads and how often he or she has to thin it out.
Look how many morning glory seedlings have popped up in the lawn from the previous year’s plants.
Also ask how freely it seeds because some plants churn out seedlings all over the yard for years. Four plants that taught me that lesson are morning glories, nigella (love-in-a-mist), hardy ageratums, and bronze fennel.
With any luck, the giver will know the name of the plant, too. That’ll let you look it up in a good garden book or online before planting. Be wary if any descriptions mention words such as “invasive,” “aggressive,” or catalog-writers’ favorite code word, “vigorous.”
The state Department of Conservation and Natural Resources has an excellent web page on recognizing and dealing with invasive plants, and the state Department of Agriculture has the official list of plants deemed invasive in Pennsylvania on its website. You’ll definitely want to avoid anything on that list.
The Ag Department’s Controlled Plant and Noxious Weed Committee has a further list of plants worth considering for noxious-weed status.
Where you decide to plant a pass-along can make a big difference as well.
Example: A neighbor may have a planting of variegated lamiastrum or ajuga that looks to be under reasonable control mass-planted under a big shade tree. But if you take divisions of those same plants and put them in good soil in a perennial border, they quickly become thugs.
The lesson is that aggressive species sometimes make sense when they’re harnessed by dry shade and root competition and/or given plenty of unimpeded space to spread. Remove those checks, though, and it’s like unleashing smallpox on a new town.
Beyond the invasiveness issue, decide if you even like the look and habit of the plant. Ask yourself if there’s a spot in your yard where it’ll fit in and make sense. Don’t ruin an otherwise nice design with a newcomer just because it came free.
Here are eight plants that people often try to give away that are high on my “just say no” list: 
* Chameleon plant (Houttuynia). A short groundcover with beautiful multi-colored leaves. Problem is, it sends out runners everywhere.
* Bamboo. Some types are fairly well-behaved clump-formers, but the spreading types can put out runners that go under a driveway and come up on the other side. This plant does not respect property lines, so it’s a threat to neighbors as well as your back when trying to control it.
* Ribbon grass (Phalaris arundinacea var. Picta). A white-edged grass that spreads mercilessly, especially in damp soil.
* Tawny daylily (Hemerocallis fulva). This is the orange bloomer you see growing en masse in roadside ditches and wood’s edges in June. It’s pretty for two weeks but then tough enough to elbow out most any neighbor as the clumps spread relentlessly.
* Purple loosestrife (Lythrum salicaria). This long-blooming perennial with the spiky pink-purple flowers was banned years ago for its invasive seeding, but gardeners still have clumps of it that they divide and try to give away.
This bishop’s weed is aggressive enough to overtake neighboring Japanese pachysandra.
* Bishop’s weed (Aegopodium podagraria). The variegated leaves are attractive, but it’ll usually spread out of control in even marginal conditions. Some people call it “snow-on-the-mountain.”
* Lemon balm. The lemony scent is nice, but this herb creeps and seeds and roots to the point where most gardeners end up ripping it all out.
* Spearmint. Another nice-smelling herb that’ll creep for miles if you let it. If you get a division, grow it in a big pot, not in the ground (unless you encase it in a buried chimney flue).
Some others you might want to think twice about… lily-of-the-valley, snow-in-summer, dame’s rocket, tansy, creeping bellflower, obedient plant, yellow flag iris, crown vetch, English ivy, Johnny-jump-ups, and seedlings of butterfly bush, burning bush, barberry, and rose-of-sharon.