Bull Thistle Invasive plants in your lawn: Japanese Stiltgrass and Bull Thistle

What is all the fuss about invasive plants?

Invasive plant species can pose quite a challenge. Because they grow aggressively and displace native plants, invasives can upset the balance of existing ecosystems. They are difficult to control and tend to dominate whole areas, making them highly undesirable.

Why are invasive plants such a problem?

Without natural predators, pests or disease to keep them in check, invasives spread rapidly. Bull Thistle, for example, was introduced into the US during the 19th century and is now established in all 50 states, several of which have designated it as a noxious weed.

Japanese Stiltgrass

Japanese Stiltgrass, native to East Asia, is believed to have accidentally arrived in the United States through its use as a packing material. Each plant can produce up to 1,000 seeds annually and each seed can live up to five years. Given sufficient soil nutrients and moisture, the plant can tolerate lowlight environments and conversely, with adequate light, it can survive in low-nutrient and low-moisture environments. Once established, Japanese Stiltgrass can form dense monocultures that suppress most native understory plants.

What can I do about invasive plants in my lawn?

Prevention is one way to control invasives. Act quickly to remove them when they first appear in low numbers or are confined to a small area, before they become a bigger problem. Be sure to dispose of invasive plants carefully and replace them with natives and noninvasives.

Trees in Grass

To prevent Japanese Stiltgrass from spreading, mow late in the growing season (August-September) when plants are flowering but before seed has set. Early season mowing won’t help because plants will soon respond with new growth and flower production and banked seeds can still produce a new crop of seeds by the end of the growing season.

One of the best ways to keep invasive plants out of your lawn is to make sure your desirable grass is as robust as possible. A healthy lawn can out-compete weeds and invasive plants.

A comprehensive lawn health care program includes:

  • Soil Analysis
  • Proper watering and mowing
  • Pre-emergents (these are key to controlling Stiltgrass) with additional controls timed property
  • Appropriate fertilization
  • Core aeration and overseeding


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