Repairing small spots now can help prevent more weeds later. View more lawn care videos.

By Frank Rossi

Editors note:  Rossi is a turf specialist and associate professor in the Department of Horticulture, Cornell University.  This is the first in a series where Rossi debunks common lawn myths.  His advice targets cool-season grass growing regions in the Northeast, but may be applicable in regions with similar growing conditions.

ITHACA, N.Y. – It’s a sure sign of spring:  The robins return and millions of lawn owners head out to apply fertilizer and weed- killers to their lawns – a rite widely known as “weed and feed.”

But here’s the problem:  Early spring probably isn’t the best time for you to fertilize your grass or apply herbicides unless you have a history of weed problems.

Let’s start with the herbicides.  Weed and feed products designed for early-spring application usually contain pre-emergent herbicides.  They work by preventing weed seeds from sprouting, and they can be an effective way to control crabgrass and some broadleaf weeds.

Trouble is, this assumes that you’ve got weed seeds in your soil ready to sprout.  If you’ve been using pre-emergent herbicides regularly or otherwise doing a good job of controlling weeds and keeping them from going to seed, you may have exhausted the supply of weed seeds in the soil.  If that’s the case, applying pre-emergent herbicides is like clapping your hands to keep the lions away.

Then there’s the fertilizer.  It should be mostly nitrogen, and I’ll admit that it can really green up the grass in a hurry.  But it can also fuel lush top growth at the expense of roots, and you want those roots going deep for moisture so the grass can outcompete weeds during the hot, dry summer months to come.  That lush top growth also means you’ll need to mow more often and deal with more clippings.

If you’re going to apply fertilizer, Memorial Day and Labor Day are better times to do it.  And with recent restrictions on phosphorus fertilizer in many areas and the lack of evidence that potassium will improve your lawn in most circumstances, shop around for fertilizers that are all nitrogen.

Other weed and feed products are designed for late-spring application.  They contain herbicides designed to kill actively growing broadleaf weeds like dandelions.  But if you want to kill broadleaf weeds, these herbicides are much more effective if you apply them in fall.  At that time, the weeds are storing up reserves for winter and moving nutrients from the leaves to the roots.  They move the herbicide to the roots at the same time, resulting in a better kill.

And unless your weeds are running rampant, try spot spraying them in the fall instead of putting down herbicide over your entire lawn.  That’s just one small step you can take for sustainability.

If weed and feed has become a ritual for you, it’s time to break the habit.  Try skipping it this year and applying fertilizer and herbicide only if you need them and in separate treatments at the times when they will be most effective.


More spring tips:

Rossi offers these tips to get your lawn off to a good start in spring:

  • Stay off your lawn until it dries out.  Foot traffic on soggy lawns can damage grass and cause soil compaction.
  • Rake up surface debris that shades grass. You don’t need to rake aggressively.
  • Seed thin areas and damaged spots. “Spring is a race for space between grass and weeds,” says Rossi. “If you can see soil, broadcast and rake in grass seed to fill that space.”
  • Repair salt damage along sidewalks and driveways. The usual advice is to water these areas to leach the salt from the soil.  But if salt damage is severe, the soil will lose its structure and become compacted.  “You’ll just end up with a big puddle and runoff,” says Rossi.  You may need to remove and replace the soil to solve the problem.
  • Start mowing. Rossi usually suggests raising your mower as high as it will go.  But on the first mowing, he suggests lowering it slightly.  “Topping it off an inch or two shorter will help the soil warm up and encourage early growth,” he notes.

More information:

Next month’s installment:  Mowing myths exposed.

Leave a Reply