Usually, I am not one to really worry about weeds in the landscape. There is a reasonable threshold for weeds in turf and a few in landscape beds as long as they aren’t in front of doors or along sidewalks where people walk every day.
However, if you are going to get rid of them, now is the time to do it.
Labor Day to the first hard frost, most plants – including weeds – are moving nutrients from the leaf tissue down to the roots for winter storage. By treating your turf with a broadleaf herbicide during this time, the weeds move the chemicals from their leaves to their roots with ease, resulting in much higher percentages of dead plants.
This is especially true with dandelions. If you want to reduce the amount of chemicals you use or are on a tight budget, a fall spray for dandelions is the best thing for you.
Dandelions are biennials, meaning they generally live only for two growing seasons. By spraying in the fall, you kill off all of the seedlings that have sprouted over the summer that would emerge in spring as big, healthy dandelions in spring. You are killing off a majority of the plants that will be blooming the next spring and you will be able to simply spot spray to handle the rest.
Fall is also very good to kill other weeds like violets, thistle, spurge, yarrow, creeping charlie and clover.
Over time, you can have a very successful, albeit less-than-perfect, turf program with a combination of fall treatment for weeds with a fall application of fertilizer to encourage root growth in your turf.