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Weeds — get them before it’s too late

In the Garden

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The problem with weeds is, like bad habits, we don’t recognize them until it is too late.

Weeds fall into one or two of five different categories:

  • Summer annuals
  • Winter annuals
  • Biennials
  • Simple perennials
  • Creeping/spreading perennials

With the recent rains and cooler weather, you may have noticed a lot of little plants germinating around your yard. Right now is the best time to control most of the weeds we see in the spring. The weed categories that respond best to fall weed control activities are winter annuals, biennials, simple perennials, and creeping/spreading perennials. I will discuss fall weed control options under the umbrella of integrated pest management.

Ron Patterson, UI Horticulture Educator


  • Learn to identify common weedy plants, especially annual seedlings and biennial rosettes.
  • Keep all weedy plants from producing seeds.
  • Organic material brought in to your garden may carry viable weed seeds.


  • Cultivation does not need to be deep for seedlings.
  • Hand pull large plants before they drop their seeds, and dispose of plants that have seeds on them.
  • Remove biennial rosettes with a shovel by severing the root two to three inches below the crown.
  • Simple perennials, such as dandelion, are not as easy to control mechanically, but they can be set back by severing the root two to three inches below the crown.


  • Flame weeding is typically done with a propane weed burner. Direct the flame at the base of the seedlings. Don’t burn them to a crisp, simply wilt the main stem. Flame weeding is not effective on established perennials and biennials, or on grasses.
  • Mulch is best 3 – 6 inches deep, and the best organic mulch is wood chips rather than wood shavings or bark. A weed barrier can be placed under the mulch, but it should be breathable material and will likely need to be replaced in a few years. Weeds that germinate in the mulch on top of the weed barrier are usually easier to pull.
  • Employ practices that encourage healthy, desirable plants.


  • Biological control (bio-control) options are specific to a plant family, genus or species. Bio-control agents that are approved for release in Idaho can be found here.
  • There are many native bio-control agents, but keep in mind that they will not eradicate a weed population. They will not eat themselves out of house and home.

Chemical—the last tool to consider

  • There are organic and non-organic burndown herbicides which should work well on many of the fall seedlings.
  • Herbicides are much more effective on seedlings than they are on larger plants.
  • Select herbicides that have your specific weeds on the label.
  • Most perennials respond better to fall herbicide application as that is when the plants are drawing energy reserves back to the roots.

Pleasant fall conditions don’t last long in eastern Idaho, so take advantage of this beautiful weather to help make your spring much more enjoyable.

Ron Patterson, UI Horticulture Educator