Spring weeds pop up fast. If you're not careful, they'll crowd out the growth of new grass and plants, taking over before summer. Knowing when to spray common weeds goes a long way, and once you can stop them early, you'll have a lot less work the rest of the season. Whether you're using a post-emergent weed killer, like a contact spray, or thinking about a pre-emergent application option, planning matters.
When to Apply Weed Killer in Spring
The best time for spring application is when weeds are small and just starting to grow. That's when they're easiest to kill. Spruce is a non-selective contact spray that aims (pun intended) to be an effective choice for families and pet owners. “[You should] spray Spruce thoroughly when weeds are small but actively growing,” shared Dr. Douglas Doohan, Weed Scientist with the Spruce Alliance. “And, spray until all leaf surfaces are thoroughly covered and wetted by small droplets of the herbicide.”
Good coverage helps make sure the spray sticks and gets absorbed. Spruce contains ingredients like cornmint oil, geraniol, and sodium laurel sulfate to penetrate and dehydrate the plant tissue. It will also dehydrate and kill annual grasses and plants in your flower garden, so targeting tough weeds is important. We prefer using it in our landscaping beds and between pavers on the patio instead of in the lawn.
You want to look for early signs of weed growth; it won't work on weed seeds. “Look for newly developing ‘baby’ leaves, that are bright green in color, and getting larger over several days,” notes Doohan. When you begin to see weed foliage, this is your window. Wait too long, and broadleaf weeds grow stronger—and harder to get rid of.
Many homeowners still use granular pre-emergent herbicide to manage weed seed germination across an entire lawn. Keep in mind that this type of herbicide acts like a blanket. This blanket can also stifle the germination of grass seed. Also, check the ingredient list closely... many contain harmful chemicals.
Weather and Temperature Matter
Most types of weeds need the soil temperature to warm up before they sprout. If the weather is too cold, they won't grow. And, if it's too wet, your weed killer won’t work as well.
Spruce is a contact herbicide, so the leaves need to be dry and the air needs to be warm. Doohan recommends spraying “on sunny days when the air temperature is 60F or higher.” If rain is coming soon, try to hold off, but if it rains later that day or in the days after application, you're in the clear. “Don’t spray while it is raining or if rain is about to start. If it does rain after application, but more than 10 minutes have passed, you can still count on good weed control.”
What About Dormant Grass and Pre-Emergent Weeds?
Contact weed control products like Spruce only work on plants in their active growth cycle. If you spray them on dead or dormant types of weeds, you won’t get the result you want. Doohan explains, “Don’t spray Spruce until there are clear signs of growth; bright green color and definite evidence of growth including formation of new leaves’.”
So if you're looking at clumps of brown grass or old, pesky weed patches, wait until you see new growth. If you want to stop the weeds before they come up at all, you'll need a pre-emergent weed control product instead. Contact sprays won’t help with weed seeds still under the soil.
How long does it take to see results after spraying?
Most post-emergent herbicides suggest that you'll start to see the toughest weeds wilt within a few hours, with full results in a day or two. We tested Spruce on perennial weeds and saw visible deterioration within an hour from the application time; the plant appeared dead within a day. Of course, I imagine that it can vary depending on weather, weed type, and how well you covered the leaves.
