Just because the growing season is winding down doesn’t mean it’s time to give up on or forget about troublesome weeds on the lawn.
Early fall is actually one of the best times of the year to control lawn weeds, mainly perennial weeds – the ones that typically die over winter before resprouting from their roots the following spring.
Some of the most common perennial lawn weeds include:
- ground ivy
- wild violets
- wild strawberry
Why fall is good timing
As temperatures drop in fall, perennial plants – including perennial weeds – prepare for winter dormancy by moving sugars manufactured in their leaves into their roots for winter storage. This action increases the effectiveness of herbicides that hitch a ride on the downward “translocation,” improving their ability to kill weed roots.
A few perennial weeds that sprout in fall and spring, including dandelions, plantain, and speedwell, are also more susceptible to fall herbicides because of their youthful vulnerability.
Both granular and liquid herbicides work better on perennial broadleaf lawn weeds in fall than in spring or summer. They’re best applied around and shortly after fall’s first frost on days that reach at least 50 degrees. (Perennial weeds typically survive the season’s first few frosty nights.)
Granular herbicides make the most sense when weeds are everywhere since the granules can be broadcast over a wide area. Preen Lawn Weed Control, for example, is a granular product that kills more than 200 species of broadleaf weeds in lawns.
Liquid herbicides make more sense for spot-spraying patches of weeds here and there, limiting herbicide use only to where it’s needed.
In both cases, read herbicide labels carefully for safety and effectiveness tips as well as to make sure you’re using the right product in the first place. A common mistake is using a non-selective or “kill-everything” herbicide such as glyphosate or glufosinate in the lawn. These not only kill lawn weeds but turfgrass, too. To kill lawn weeds without harming turfgrass, look for an herbicide labeled for the control of broadleaf weeds in lawns. These typically include such active ingredients as 2,4D, dicamba, triclopyr, MCPP, and carfentrazone.
Pay particular attention if you’ve seeded or overseeded the lawn in late summer or earlier in fall. Lawn herbicides can damage young grass seedlings, typically until they’ve grown for at least three or four weeks and been mowed two to three times. The product label should recommend when it’s safe to apply to recently germinated grass.
Controlling other lawn weeds in the fall
Perennial grassy weeds such as quackgrass, bermudagrass, nimblewill, and nutsedge can be controlled to some degree in the lawn, but since they’re so botanically similar to turfgrass, herbicide options are limited, if available at all. Most of those weeds must be dug out or killed with a non-selective herbicide. Then the bare area can be seeded with new grass.
Read more on how to control grassy weeds on the lawn
Most biennial lawn weeds also can be as effectively controlled in fall as perennial broadleaf weeds.
Biennials are plants that sprout from seed and grow leaves the first year, then overwinter to flower, drop seed, and create new plants before dying in the second year.
As with perennials, first-year biennials also store sugars in their roots and are susceptible to fall herbicides.
Examples of biennials are:
- garlic mustard
- wild carrot
- prickly lettuce
Finally, winter annuals are another group of weeds that can be controlled in fall. These are plants that germinate from seed in the cool soil of fall and early winter, then grow and flower early the following year.
Recently sprouted winter annuals can be killed with the same herbicides that kill perennials and biennials, while fall-applied weed preventers can stop most new winter annuals from germinating.
Preen One Lawncare, for example, is a three-in-one product that can be used in fall to prevent the germination of winter annuals as well as kill existing broadleaf weeds, and fertilize the lawn.
Examples of winter annuals are:
- purple deadnettle
- yellow rocket
- mare’s tail
- hairy bittercress