Is it Wise to Spread Rose of Sharon Seed in the Wild
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---Pauline in Reading, Massachusetts
A. This reminds me of my old friends in the 'Green Guerilla' gardening group 'seed bombing' a vacant lot—except that a lake shore is not a vacant lot! You can do a lot of damage to a wetland by randomly spreading seed around. And my Spider-Sense started tingling independently of the water angle on this one, as I feared that there might be problem plants involved.
Obviously the devil is in the details, so I emailed Pauline to ask what specific "perennials" she's talking about.
Her response: "I have a mix of sunflowers, phlox, coneflower, black-eyed Susan and rose of Sharon. I know my idea may sound crazy," she continues, "but I couldn't stand the thought of just tossing them in the compost!"
Well, at least one of these IS a potential problem: the 'Rose of Sharon'. It's not a rose of any kind, but a hardy hibiscus—and I mean 'hardy', as in potentially invasive.
How invasive is it?
So invasive it was named "weed of the week" by the USDA Forest Service back in 2006! They describe this Asian native as "a prolific seeder with a deep taproot that is difficult to remove once the plant is two or three years old." Listed as officially invasive by at least four states—including PA—it has "escaped intended plantings to invade, crowd out and displace more desirable native plants."
I've seen this in my own landscape; one just 'appeared' in my front yard several years ago, and is now huge—and I have to keep pulling up the volunteers that show up in other parts of the yard every few seasons.
So why don't I just cut it down?
It blooms late in the season, when there aren't a lot of other things in flower. And it attracts pollinators and hummingbirds, who don't have a lot of other sources of pollen and nectar at that time of the year. I do pull up the volunteers before those famous taproots can become established; and I keep a close eye on the woods. The minute I see that one has gotten into the wild, I'll cut it and mine down and nail a coffee can over the stumps. But I hope that never happens. Anyway, if aggressive plants like these 'appear' next to a lake as opposed to in a kept front yard, there probably wouldn't be a human caretaker to try and control them. That lakeside could become a forest of hardy hibiscus in twenty years. Even worse, the plants could attract the attention of invasive plant eradicators spraying potent chemical herbicides.
But if you're starting fresh, you could have your Rose of Sharon without risk; just choose one of the many sterile cultivars that are available. And there are options beyond the Asian Hibiscus syriacus we've been discussing. There's a "Swamp rose mallow" (Hibiscus moscheutos) that's native to a wide range of North America (USDA Zones 5 to 9) and another 'swamp' version that's native to really wet areas in the American South (Hibiscus coccineus).
But back to the topic. I'm a little surprised that our listener saved seeds without seeming to have had plans for them, but most gardeners would welcome the coneflower seeds she mentions—and the sunflowers (which are annuals; not perennials). Maybe even the Rose of Sharon with a little bit of warning.
Correctly labeled, she could donate the seeds to a public library that has a 'lending library' of seeds. Or take them to a local seed swap; the Master Gardener volunteers at her local County Extension office should know where and when such things are happening locally.
And I'm going to go back to something we mentioned in the beginning: rolling the seeds into balls of mud and tossing the resulting 'seed bombs' into vacant lots in a big city. Not the ones on her list that have the potential to spread like phlox and Rose of Sharon, but the very pretty non-invasive ones—like the sunflowers, Echinacea and Black-eyed Susan. They would brighten the day of passers-by and make life much better for inner city bees and beneficial insects. But that's only if they're sorted out; if she really has a 'mix' of seeds in a jar, it's into the compost pile this season.
But if she carefully harvests and labels this year's crop she can safely yell "bombs away" at this time next year.