Category: Invasives

Managing Invasive Japanese stilt grass

Japanese stilt grass will always require regular management to prevent it from overtaking our woodlands, lawn, and gardens. We’ve found specific routines help keep this highly invasive grass well controlled.

Young Japanese stilt grass

Japanese stilt grass.

These simple steps allowed us to reverse a massive stilt grass invasion in our Connecticut (zone 6) landscape:

  1. Monitor all garden beds, woodlands, under trees and shrubs frequented by birds from early summer through September for stilt-grass.
  2. Hand-pull all.
  3. Young plants that you pull – those that have not started to seed – can be left in place to dry and die.
  4. Any stilt grass that has begun to develop seed heads – anytime between mid-August to mid-September – must be disposed of in the trash. Do not add stilt grass or any invasive plant to your compost pile.
  5. Mulch areas where stilt grass has been found with shredded leaves or shredded hardwood to minimize regrowth from seeds in the soil.
Japanese stilt grass

Japanese stilt grass

Getting a large invasion of Japanese stilt grass under control was a multi-year effort using different techniques outlined in Tend to Japanese Stilt Grass NOW! back in 2013. Read this post for lots of info on this highly invasive plant.

The lawn area torched then had a wonderful regrowth of perennial lawn grasses. While small sections of stilt grass have regrown each year from seeds previously deposited in the soil, we’ve controlled these with mowing and hand-pulling.

Japanese stilt grass loves to grow along woodland edges. We found that maintaining a good six-inch layer of fallen leaves prevents most stilt grass from sprouting. The occasional stilt grass plant that does sprout is easily controlled by hand-pulling.

Vigilant trolling for mature Japanese stilt grass plants in September – when they are in seed – is most critical. Do not let stilt grass seeds mature. Each seed head can deposit up to 100 seeds in the soil. Each seed can be viable there for seven years.

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Seed dispersal with gusto

Some plants passively count on wind, creatures, or water for seed dispersal. Other plants attack seed dispersal with gusto, creating a type of seed pod firework display.

The video below shows seed dispersal with gusto, a process I’ve observed this many times in my Connecticut gardens.

Unfortunately, the video only refers to the plants by common name – violets, touch-me-nots, squirting cucumbers. Searching for information using only common plant names can lead to confusion as common names may vary from gardener to gardener and region to region. For anyone looking to add featured plants to their garden, the addition of botanical names would have been helpful.

In Connecticut, touch-me-nots are also called jewelweed. The Connecticut Botanical Society (CBS) lists two native species: jewelweed or spotted touch-me-not is Impatiens capensis, while pale touch-me-not or pale jewelweed is Impatiens pallida.

white violets

white violets-a CT native using seed dispersal with gusto

CBS also lists many species of violets, most in the Viola family such as the common blue violet (Viola sororia) and small white or northern white violet (Viola pallens). By contrast, CBS does not list poisonous-when-ingested squirting cucumbers (Ecballium elaterium), native to Mediterranean regions.

Seed dispersal with gusto is a fun phenomenon for desired plants. In my landscape, common blue violets add interest and color to the lawn, where I encourage their spread, and where they attract some of the earliest emerging pollinators. But the same blue violets require annual control in perennial beds to prevent them from taking over.

Two of Connecticut’s weedy invasives hairy bitter-cress (Cardamine hirsuta) and garlic mustard (Alliaria petiolata) need only a slight touch to blast mature seeds in all directions, making them formidable weed pests. Hairy bitter-cress blooms during very early spring going from flower to mature seed in just a few days, and re-blooms late-summer to fall from these broadcast seeds. If not caught before narrow seed pods dry, plant removal is impossible without spreading seeds. Garlic mustard is similarly robust in seed dispersal.

Informed gardeners can use seed dispersal knowledge to their advantage by allowing desired perennials to go to seed, or preventing unwanted weeds or perennials from doing the same.

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