Invasive Species Tips

Our yards and landscapes suffer under a continuous attack of brutal exotic invaders. Once you recognize these enemies, you see them everywhere: Japanese barberry, winged euonymus, privet, multiflora rose, Japanese honeysuckle, mugwort and Japanese knotweed. And the list goes on.

All these plants crowd out our native plants, on which our pollinators and birds depend as food sources.

Tackling this issue in our woodlands requires measures beyond the scope of homeowners alone.

Healthy Yards advice: Don’t let the bullies intimidate you! A good strategy is to have a look around in your yard and decide how much you can manage and then start removing ONE species after the other.

Start with the most aggressive spreaders first:

In Europe this plant is charmingly called Modest Henry, which illustrates how complicated the issue of invasives is: outside of its natural habitat, a plant can gain completely new characteristics.

Here in the USA, garlic mustard has a strong allelopathic capacity, which means it doesn’t just crowd out other plants, but it also makes the soil less suitable for them to grow in.
  • Removing garlic mustard is fairly easy:
  • Remove it before it goes to seed¬†
  • Remove root and all
  • It’s a biannual: Learn to recognize the first-year plant and get that at the same time
  • It’s easiest to remove after rain when the soil is soft
  • Keep at it!¬†
  • Dispose of seed heads in the¬†trash or commercial compost facility
  • Replace with part¬†shade loving plants: packera, creeping phlox, wood anemone, or any other native plant you can get hold of
  • The good news: once you have removed this,¬†natives from the old seed bank will start growing again

Again a beloved wet soil loving spring flower in Europe, but here it’s an unstoppable plant crowding out all our spring ephemerals. Lesser celandine creates a massive and thick underground structure, composed of a mass of bulblets and roots, so dense that there is no¬†room for other plants. The window for removing this plant is short and its removal is tedious. Get it as soon as you see it appear in your yard — don’t pause to admire its pretty yellow flowers or glossy leaves, or else you will be run over!
  • Prioritize natural areas, celandine has little impact on turf, but is disastrous for our¬†natives ephemerals
  • Start¬†where the plant seems happiest and go from there
  • Remove ALL roots and bulblets (every little piece will regrow!)
  • Replace immediately with moisture-loving natives as skunk cabbage, wood poppy, wild leeks
  • Dispose of all the plant material in the¬†trash or a commercial compost facility (or feed it to your chickens if you have them!)
  • Keep at it!
  • In Europe the soil contains nematodes- microscopic worms- that keep Lesser celandine from becoming a nuisance. Using animals species to control invasive is called Biological control. Biological control with imported species has risks and¬†requires a period of study to ensure it will not harm other species.

Japanese Knotweed and Mugwort are bordering most of our roadsides today with dense rhizome-rich patches, but they are also unwelcome and greedy guests in our yards.
  • Wait for after heavy rain so roots can easily be pulled
  • Remove all roots or every little piece will regrow!
  • Japanese knotweed and Mugwort love nitrogen:¬†don’t fertilize these areas.
  • The roots can be so dense that pulling is no option,¬†in that case keep¬†mowing the area and removing the plant debris, until bare patches appear.
  • Replace pulled roots, or use the bare patches to fill,¬†with strong rhizomatous native wildflowers such as monarda, mountain mint, wild geranium, milkweed, primrose, goldenrods
  • Use non-systemic herbicides only as a last resort
  • Dispose of all the plant material through the trash or a commercial compost facility
  • Keep at it!¬†
Japanese stilt grass is last on our list. It might take over the landscape at the end of summer, but its roots are very shallow and do less damage to our native habitat than the species above. It is an annual grass and its small seeds spread everywhere.
  • Pull Stilt grass before the seed¬†heads are formed.
  • Replace with tall, late summer flowering, part shade-loving plants, such as goldenrods and asters
  • Keep pulling:¬†the wind will bring in new seeds every year.

Interesting enough, Stilt grass¬†serves as a host plant for some native satyr butterflies, such as the Carolina Satyr and the endangered Mitchell’s Satyr.

Thank you to Healthy Yards for these great tips!