Fall Broadleaf Weed Control: Why October Beats Spring

If you only have time to fight broadleaf weeds once a year, do it in the fall. Dandelions, clover, plantain, ground ivy (creeping Charlie) and other perennial broadleaf weeds are at their most vulnerable from mid-September into October, and university turf programs across the northern states say the same thing. Here's why, and how.

Why fall works better

In fall, perennial weeds are storing food for winter. They move sugars from their leaves down into their roots. A systemic broadleaf herbicide applied now rides along with that flow and gets carried down into the root, which is what kills a perennial weed for good. In spring, the flow goes the other way, up into new leaves and flowers, so a lot of what you spray never reaches the root.

There's a bonus: the lawn is growing strongly in fall, so it fills in the spots where weeds die before spring weeds can move in.

Timing

• Apply when weeds are actively growing, usually from mid-September through October across most of the northern US.
• Daytime temperatures in the 50s to 70s are ideal. Most products work poorly when it's cold, and some can damage the lawn when it's hot.
• After a light frost is fine, as long as the weeds are still green and growing. Some research suggests an application after the first light frost can be especially effective on tough weeds like ground ivy, because they're pulling food down hard.
• Don't apply before rain or when the lawn is drought-stressed. Read the label for how long it needs to dry.

Spot spray, don't blanket

Most lawns don't need the whole yard treated. Spot-spray the weeds you can see. You use far less product, spend less money, and keep it away from trees, shrubs and gardens. If weeds cover most of the lawn, a broadcast treatment may make sense, but that usually means the lawn needs feeding, overseeding and better mowing more than it needs more herbicide.

Read the label

The label is the law, and it tells you what weeds a product controls, the rate, the temperature range, and how long to wait before you seed. Many broadleaf products require waiting several weeks before seeding, so plan your fall overseeding around it. Keep kids and pets off treated areas until the product has dried, or longer if the label says so.

The long game

Weeds move into thin lawns. The best weed control is a thick lawn: mow high (3 inches or more during the season), feed in fall, and fix bare spots. Our visual guide to common lawn weeds shows you what you're dealing with. Hit the broadleaf weeds this October, follow with the late-fall feeding, and you'll be amazed how few dandelions show up in May.

Photo: 2019-04-30 18 04 39 Dandelion flower in a lawn along Tranquility Court in the Fr by Famartin, CC BY-SA 4.0.

Related: Nutsedge Control in Northern Lawns: Why It’s Different from Other Weeds