Aaron Patton/Purdue Extension
To defeat crabgrass, which grows very flat, you need to dig it out to remove next year's seed crop.
Backyard Battleground: Fall is the time to combat weeds
Fall is a great time to fight weeds, so that you won’t have as many next year.
There is a temptation to just “let it go,” but annual weeds will produce lots of seeds, and perennial weeds will be bigger in addition to spreading by seeds or roots, so this is the time to get on top of it all.
In the cooler fall weather I find it delightful outdoors. The sun has lost much of its heat, so I can work in sunny areas without getting too uncomfortable. Just taking a deep breath of the fall air makes me want to get out there and do some hard work.
Many people don’t keep up on the weeds in their vegetable garden in the heat of summer. I don’t get many weeds because I follow these practices: I dig out any weeds, remove remaining vegetable plants, then smother the vegetable garden area with a thick layer of leaves as soon as they start falling. This prevents the weed seeds from germinating, as well as inviting worms and other soil organisms to aerate and improve the soil. Chopped leaves will be least likely to blow away, but if you wish to stabilize whole leaves, you can do so with chicken wire or a tarp.
This method may also smother many weeds, but I prefer to remove them to make sure that there are no seeds to start next year’s weed crop. Rototilling in the weeds ensures that they will get off to a good start next year, planting the seeds and breaking up perennial roots so they can make lots of new plants next year (yikes!). Rototilling also damages the soil structure, making it less inviting for roots and soil organisms.
Often there are thaws over the winter, during which I may stir up the leaves with my long-handled claw cultivator. This incorporates more air, better enabling decomposition when the temperatures are above freezing. Ah, this smell in winter nourishes my soil-starved soul.
I am also working to reduce the crabgrass in a few areas of my lawn. It is an annual grass, and I have been putting down a pre-emergent treatment to keep it from germinating. May is the recommended time, because the soil isn’t warm enough before that. The pre-emergent chemical stops working in the hot weather of July, so I have found that is isn’t terribly effective because the crabgrass continues to germinate. I think you really need to dig it out, removing next year’s seed crop. It grows very flat, under the more upright grasses, ensuring that next year’s seeds will get good soil contact. There are lots of photos on Google images if you need help in recognizing it.
Poison ivy and other invasive weeds may also be most effectively treated in fall. If you spray with glyphosate (RoundUp) when the leaves are still green, it will better absorb this chemical into the root system as the plant goes dormant, killing it with fewer applications.
Julie Brocklehurst-Woods has been a Master Gardener Volunteer with Cornell Cooperative Extension of Livingston County for over ten years. She enjoys helping all gardeners become successful gardeners, especially helping people identify tools and strategies to prioritize and simplify their gardening tasks. She works part-time as an occupational therapist with Finger Lakes DDSO.