Different weeds require different control tactics. In order to know your best method to kill any particular weed, you need to understand it – how it grows, when it grows and the best time to attack it.
From the moment annual weeds sprout, they’re racing to flower and set seed. Your job is to interrupt the process. If you can’t kill weeds or pull them shortly after they appear, make sure you deal with them before they set seed.
When you’re facing a crop of annual weeds that have set seed but not dropped them, you might be able to use your mower – with grass-catcher bag attached – to cut and collect seed. This method works well with grassy lawn weeds, such as quack grass and goose grass. Rake weeds before mowing to pull seed stems upright. After mowing, destroy or dispose of seeds – don’t add to your compost pile. Be careful not to rake if seeds are dropping, or you risk spreading seeds.
As soon as perennial weeds sprout, it’s time to take action. With taprooted weeds such as dandelion, pulling young plants improves your odds of removing the entire root.
If you miss this opportunity, you’ll need to coerce mature tap- or tuber-rooted or perennial weeds into submission – and eventually death – by consistently removing or treating foliage with herbicide as it appears. For grassy weeds such as nutsedge, treat before six leaves appear. For broadleaf weeds, treat when leaves have just unfolded but before they have time to start replenishing root stores.
If you use this technique on dandelions, you’ll wipe out most plants with two treatments. With more stubborn weeds, this process could continue for multiple seasons, but it might help you to know that it is worth your time to keep up the effort. Every time the plant pushes out new leaves that are killed, that effort is depleting food supplies in the root. At some point, food reserves will run out, and the plant will die.
Killing Weeds: Pulling vs. Spraying
Pulling weeds by hand is a task that’s most approachable when you’re dealing with a small area or just a few weeds scattered around a large space. Weeds come up easiest when soil is moist and plants are small. When pulling perennial weeds, make sure you remove roots. With many perennial weeds, root pieces left in soil will sprout.
Spraying herbicide plays an important role when you’re clearing vegetation from an area or when you’re dealing with weeds you can’t eradicate any other way. Learn specific tips for applying herbicide.
Preventing a Problem From Sprouting
Probably the easiest way to kill weeds is to keep them from gaining a foothold. Use a pre-emergent herbicide to prevent weed seeds from germinating in planting beds and lawns. Timing is critical; follow label instructions carefully. Don’t use pre-emergent weed killers in beds where you plan to sow seeds – the herbicide may prevent your seeds from germinating as well.
In planting beds, a 2-inch-thick mulch layer can suppress weeds, as can tightly spaced plants, which don’t give weeds the necessary elbow room – or sunshine – to survive.
In early spring or late fall (even after hard frost), perennial weeds can appear green, which may tempt you to apply herbicide. Don’t be fooled. When temperatures are low, plants aren’t actively growing. Watch for new leaf formation. That’s the clue to active growth – and the cue to fill your sprayer.
Other weeds become dormant during summer’s hottest days. Treating weeds with herbicide during dormancy is a waste of time and money.
As some weeds, such as crabgrass, mature, the leaves develop a hard coating that actually sheds herbicide. So while the plant is actively growing, the herbicide can’t penetrate leaves.
For many perennial weeds, such as dandelion or Bermudagrass, a late summer/early fall spray – just before plants enter dormancy – can result in effective kill. The chemical is transported to roots, which results in complete kill.
After the Weed
Weeds are opportunists. Leave one bare spot, and multiple weeds will likely appear. Once you’ve dealt the deathblow to a weed, either by pulling, digging or spraying, fill in any resulting bare spot with mulch or seed. If you’re seeding, loosen but don’t turn existing soil, cover it lightly with compost and sow seed.
For more in-depth information on herbicides, read Understanding Weed Killers.