The Pacific Northwest climate is very conducive to germination, growth and development of so called cool season or winter weeds. These are weeds which germinate in the fall and grow through the winter. These and left over summer weeds are best removed before they drop seeds for next year’s cycle. Existing weeds can be sprayed with Roundup or other brands of weed killer containing glyphosate.

This is an excellent time to apply pre-emergent weed preventers. Casoron applied to beds with woody plants will prevent weeds for an entire year. Preen and other brands of Trifluralin (Treflan) will provide about 6 weeks of protection for non-woody plants such as flowers and vegetables. Corn gluten is a natural organic weed preventer which can be used around any plants. It prevents about 80 to 90% of weed growth. Bark and similar mulches will also greatly reduce weed growth. Up to a 4 inch layer can be applied safely around most woody plants. Fall is also the best time to control broad leaf lawn weeds.


Allen Wilson

Allen has been writing about gardening for over 30 years. He is a retired professor of Horticulture.

Scroll to top