Weed Control for New Lawns: How to Remove Weeds | Super-Sod Blog

You planted the grass seed or rolled out the sod, kept up with watering, and now your lawn is growing great . . . and so are the weeds!

Before you reach for herbicide, it's important to understand why weeds appear in new lawns and the best ways to control them without harming your young grass.

At Super-Sod, we’ve been down this path millions of times, so hold steady and follow our steps to a weed-free new lawn.

The Reason Why Weeds Germinate in New Lawns: Light Exposure

It’s pretty simple, really. Since the ground is bare and has been disturbed, dormant weed seeds have been exposed to light.

Light initiates weed seed germination.

That’s it. That’s the long and the short of it.

When you kill or scrape off existing vegetation, or even disturb the ground for construction, a vast seed bank of weed seeds is exposed to light, and they go wild with growth. Tilling exposes even more weed seeds to light because it brings deep, dormant weed seeds to the surface. Even if you didn’t till, weed seeds near the surface are activated by light and further encouraged to flourish by compost, fertilizer, and extra watering.

The underground seed bank often contains weed seeds you’ve never before seen on your property – seeds that blew in, were buried, and remained dormant – waiting to be exposed. It can seem like they came out of nowhere when they have been there all along.

Even though you often bury seeds when you plant them, like with vegetable seeds, those seeds are exposed to enough light to break dormancy and start growing. However, many seed instructions specify surface sowing – that’s because those seeds need more light than others. When we advise against heavy mulching of newly seeded lawns, it’s for the same reason: the grass seed needs light to germinate, and it’s important to avoid smothering them with too much mulch.

New Sod: Weed Control in Newly Sodded Lawns

Although newly sodded lawns may face pressure from the many weed seeds already present in the soil, following these best practices can help your new turf establish quickly and outcompete unwanted weeds.

Lay Sod Right

🟢 Start off right by laying your sod rolls or pieces close together. Gently pull and stretch the individual pieces so they abut tightly. If you have seams with gaps, weeds will flourish in them.

Hand Weed

🟢 The next step is to hand-weed as much as possible. It’s okay to carefully walk across new sod (before watering, while it's a little drier and firmer) to yank out any big weeds that may outcompete or crowd out the sod, or if the sight of them is simply driving you
crazy. 

Mow as Soon as There is Something to Mow

🟢 The third step is mowing – yes, get out there on your new sod with a push mower and gently mow (avoid using a riding lawn mower because it can damage sod that’s not rooted in).

Our adage is “mow as soon as there is something to mow,” even if it’s not rooted yet. Mowing early prevents scalping and it promotes lateral growth to fill in the seams between the new sod rolls. We wrote a blog post titled "How Soon Should I Cut My Grass?" to address the nuances.

In short, if you want a 1.5” lawn, start mowing it when it’s 2” tall even if it’s not completely rooted. Look up the mowing height for your lawn. Be cautious and mow only when the ground is as firm as possible. Definitely don't mow when the sod is sopping wet. 

Continue weekly (or more frequent) mowing as the best form of weed control as it breaks the weed cycle by preventing existing weeds from going to seed.

Herbicide Timing

Timing of pre-emergent and post-emergent herbicides is the most complicated topic to cover, so please ask me any questions in the comment section at the bottom.

Pre-emergent Herbicide Timing for New Sod

"Pre" means "before," so this is the type of herbicide that is applied to kill weed seeds while they germinate, so you never even see the weed. This is a preventive herbicide that kills weeds before they emerge. Here's the timing of pre-emergent herbicide applications before and after laying new sod:

• 🔴 Avoid Applying Pre-Emergent Herbicide BEFORE Laying Sod: This type of herbicide stops weed seeds from germinating by killing the first root to emerge from the seed, thereby halting continued seed germination. This same action will kill new roots on new sod, so do not apply pre-emergent before or when laying new sod - if you have already applied pre-emergent, wait 3-4 months before laying new sod.

• 🟡 Wait to Apply Pre-Emergent Herbicide AFTER Laying Sod: Pre-emergent is an effective 3x-yearly tool for lawn weed control, so when can you start applying it on a new lawn? Because all new roots (including new sod roots) are sensitive to pre-emergent herbicides, we recommend patiently waiting until your lawn is established.
  
  ✅ How do you know when new sod is established? That's the easy part, and here are the guidelines: 1) you can no longer pull up areas of the sod; 2) all sod seams are completely filled in and no longer visible; 3) your lawn has been mowed 3-4 times; 4) one full growing season has passed. So, if you lay your sod in spring or summer, it's safe to apply the September pre-emergent application once all four criteria are met.

  🟡 🍂 Caution if Sod is Laid in the Autumn: If you laid your sod in the fall, that makes pre-emergent timing rather tricky because the seams might still be visible and you may need to skip the winter and spring pre-emergent applications until the sod has been down for one full growing season. Here are our pre-emergent timeframes for sod laid in the fall:

  • • • Zoysia - If laid in the fall, it's safe to apply after sod is 12 months old (new Zoysia is sensitive to pre-emergent too soon)

      • Centipede - If laid in the fall, it's safe to apply after sod is 12 months old (new Centipede is sensitive to pre-emergent too soon)

      • St. Augustine - If laid in the fall, it's safe to apply after sod is 12 months old (new St. Augustine is sensitive to pre-emergent too soon)

      • Bermuda - If laid in the fall, it's safe to apply after sod is 6 months old (new Bermuda, especially TifTuf, is less sensitive to pre-emergent too soon)

      • Tall Fescue - If laid in the fall, it's safe to apply after sod is 4 months old (new Tall Fescue sod is tougher and can handle the winter and spring pre-emergent applications)

         

Post-emergent Herbicide Timing for New Sod

"Post" means "after" so this is the type of herbicide that you spray on weeds that have emerged, i.e., weeds that you can see.

🟡 It's okay to apply a post-emergent liquid herbicide after you've mowed your newly sodded lawn 3 to 4 times. Check the product description/label to make sure the herbicide is labeled as safe for your lawn type.

We offer pre-emergent and post-emergent herbicides online and in our stores.

Weed Control in New Sod - At a Glance 

New Seed: Weed Control in Newly Seeded Lawns

When you till the ground to start a new lawn from seed, exposure to light activates the seed bank in the soil, as we explained above.

You may be startled that the weeds are even more vigorous in a seeded lawn than in a sodded lawn. The reason is that the ground is bare for a longer time, giving weeds extra time to germinate.

Inhala . . . Exhala . . . And just follow the protocol outlined below (it's similar to that for weeding new sod), but with a dash more patience and faith that weeds will subside over time.

Mulching Grass Seed

🟢 Use compost instead of wheat straw because wheat straw harbors more weed seeds than you can imagine. We've written tips about using compost and why to avoid wheat straw in Mulch for Grass Seeds: Cover with Compost Instead of Straw.

Hand Weed

🟢 Hand-weed as much as possible. It’s okay to walk across your new seedlings, especially if the soil is not sopping wet, to yank out any big weeds that are driving you crazy. Those big weeds can also out-compete your little grass seedlings, so it is important to weed them and get them out of the way of your new grass.

Mow as Soon as There is Something to Mow

🟢 The third step is mowing – yes, get out there on your new seedlings with a push mower and gently mow (avoid using a riding lawn mower because it can damage the baby seedlings).

Our adage is “mow as soon as there is something to mow,” after the seedlings reach the max mow height range for your lawn type. There may only be 2 or 3 blades present, but it’s already time to mow, weeds and all. We wrote this blog to address the nuances of mowing as soon as there is something to mow: How Soon Should I Cut my Grass?

Look up the mowing height for your lawn.

Continue mowing as the best form of weed control because it prevents existing weeds from going to seed.

Mowing Bonus: Mowing also promotes lateral growth in the young grass seedlings, helping them to fill in bare dirt. This lateral growth chokes out weeds and covers bare dirt, preventing new weeds from gaining ground.

Herbicide Timing

Herbicide timing before and after seeding is the most complicated topic to cover, so I'm going with bullet points again. Please ask me any questions in the comment section at the bottom.

Pre-emergent Herbicide Timing for New Grass Seed

"Pre" means "before," so this is the type of herbicide kills weed seeds while they germinate, so you never even see the weed. This is a preventive herbicide that kills weeds before they emerge. Guess what that means? It also kills your grass seedlings if applied too close to seeding!

Timing of pre-emergent herbicide applications before and after planting grass seed:

• 🔴 Avoid Pre-Emergent Herbicide BEFORE Planting Grass Seed: This type of herbicide stops weed seeds from germinating by killing the first root to emerge from the seed (the radicle), thereby halting continued germination. This same action will kill your new grass seeds, so the timing is simple: do not apply pre-emergent before or when planting new grass seed. If you have already applied pre-emergent, wait 3-4 months before planting grass seed.

• 🟡 Wait to Apply Pre-Emergent Herbicide AFTER Planting Grass Seed: Pre-emergent is an effective 3x-yearly program for lawn weed control, but new grass roots are sensitive to pre-emergent herbicide because this type targets roots. We recommend waiting until your lawn is fully established before implementing a pre-emergent routine on your newly seeded lawn.
  
  ✅ How do you know when a newly seeded lawn is established? Here are our guidelines: 1) The lawn is completely filled in; 2) it's being mowed regularly during the growing season; 3) one full growing season has passed according to this schedule:
  

  • Zenith Zoysia - Safe to apply after a seeded Zenith lawn is 12 months old

  • TifBlair Centipede - Safe to apply after a seeded TifBlair lawn is 12 months old

  • Common Bermuda - Safe to apply after a seeded Bermuda lawn is 6 months old

  • Elite Tall Fescue - Safe to apply after a seeded Tall Fescue lawn is 4 months old

Post-emergent Herbicide Timing for New Grass Seed

Remember, "post" means "after" so this is the type of herbicide that you spray on weeds that have emerged, i.e., weeds that you can see.

🟡 It's okay to spot spray a post-emergent liquid herbicide after you've mowed your newly seeded lawn 3 to 4 times. Exercise caution because new seedlings are young little plants without robust roots.

• Spot spray the weeds. That means spray only the weeds, aka "the spots," and don't spray willy-nilly all over your grass seedlings. Just hit the weeds.
• Spray them in the vening after the sun is no longer shining directly on your lawn.
• Safety depends on what weeds need to be controlled and in a particular type of lawn. Check the product description/label to make sure the herbicide is labeled as safe for your lawn type.

For broadleaf weeds, we recommend Three-D post-emergent liquid herbicide. It’s safe to apply when turf is well established at the ages below, similar to pre-emergents safety timeframes:

• Zenith Zoysia - Safe to apply after a seeded Zenith lawn is 12 months old

• TifBlair Centipede - Safe to apply after a seeded Centipede lawn is 12 months old. Note: Apply to Centipede at reduced rates and for spot treatment only.

• Common Bermuda - Safe to apply after a seeded Bermuda lawn is 6 months old

• Elite Tall Fescue -  Safe to apply after a seeded Tall Fescue lawn is 4 months old

For grassy weeds, we recommend Conduit (containing quinclorac) post-emergent liquid herbicide. It’s safe to apply at the ages below

• Zenith Zoysia - Highly tolerant and safe for use before seeding, at seeding, and after seed emergence.

• TifBlair Centipede - Not tolerant and susceptible to damage at any age. Do not use.

• Common Bermuda - Highly tolerant and safe for use before seeding, at seeding, and after seed emergence.

• Elite Tall Fescue - Highly tolerant and safe for use before seeding, at seeding, and after seed emergence.

For nutsedge weeds, we recommend Halo post-emergent liquid herbicide. It’s safe to apply when turf is well established at the ages below:

• Zenith Zoysia - Safe to apply after a seeded Zenith lawn is 12 months old

• TifBlair Centipede - Safe to apply after a seeded Centipede lawn is 12 months old. 

• Common Bermuda - Safe to apply after a seeded Bermuda lawn is 6 months old

• Elite Tall Fescue -  Safe to apply after a seeded Tall Fescue lawn is 4 months old

We offer pre-emergent and post-emergent herbicides online and in our stores.

Weed Control in a Newly Seeded Lawn - At a Glance 

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