What’s The Best Time To Spray Dandelions With Weed Killer?

Every dandelion plant that sprouts up from your lawn or border has the potential to produce 15,000 tiny seeds that will blow across your garden, ready to germinate and start the cycle again.

That is why you need to act as soon as you can to shut down this common broadleaf weed found in just about all backyards.

I like to deal with this weed in the most effective and efficient way possible — spraying. In this article, I’ll tell you the best time to spray dandelions for maximum impact and offer some expert tips to help get you started.

When Should You Spray Dandelions?

According to North Dakota State University, fall is the best time to spray dandelions. At this time, the plants are naturally redirecting energy into their roots. So applying herbicides in the fall will ensure the chemicals reach and kill the dandelions’ roots.

Each year dandelions produce the all-too-familiar bright yellow flower heads twice per season, once in spring and again in fall. The most profuse blooming is during May and June. The final flowering period occurs sometime around September.

After the flowers have bloomed, they transform into a seed-bearing sphere containing around 200 seeds per flower, with each plant producing multiple flowers each time it blooms.

Although it is best to spray dandelions in the fall when they are entering dormancy, the argument against this approach is that the damage (seeds) may already be done.

Based on this, I recommend spot-treating new weeds as soon as you see clear signs of active plant growth. I like to get ahead of blooming with the goal of reducing the overall dandelion seed density within the garden. Large-scale treatments are best applied in the fall.

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What Time Of Day Is Best To Spray Broadleaf Weeds?

The best time of day to spray dandelions is dependent on the region or, more specifically, temperature, sun exposure, and moisture levels.

Warm Climates

In warmer climates, systematic herbicides are best applied in the early morning and late afternoon when the temperature is moderate, allowing the herbicide to absorb into the plant’s foliage.

If herbicide is sprayed during the hottest part of the day, the water particles can evaporate too fast, preventing optimal absorption while scorching and drying the exterior leaves.

The opposite applies in cooler climates or seasons.

Cool Climates

Cool climates tend to have higher moisture levels in the morning and evening leading to herbicide runoff or dilution, so it’s best to apply products after this excess moisture has evaporated in the late morning through to early evening.

What Is The Best Temperature To Spray Weeds?

It’s generally best to spray weeds when temperatures are above 60 degrees Fahrenheit and when the plants are actively growing. Be sure to check that no rain is forecast and spray when the foliage is dry. Avoid applying herbicides in strong, direct sunlight to reduce herbicide evaporation.

Can You Spray Dandelions After It Rains?

It is possible to spray weeds after rain but results will be affected by the level of moisture held within the surrounding lawn or on the broadleaf weed’s foliage.

Water resting on the dandelion’s leaves will dilute the herbicide or lead to the substance running off of the leaf. The active ingredients of systemic herbicides need to be absorbed through the foliage, so it is best applied when the dandelion foliage is dry.

Spraying Dandelions On A Calm day

Depending on the type of herbicide you are spraying, you may be at risk of excess spray being carried on the wind to nearby plants or water features. I always avoid spraying on windy days and instead wait until conditions are still and calm.

Fill your backpack sprayer with your chosen herbicide concentrate or choose a ready-to-use spray. When spraying, keep the spray nozzle close to the target plants to minimize the length of the spray and avoid any stray water droplets lifting on the wind and traveling.  

Should I Spray Dandelions Before Or After I Mow?

For a systemic broadleaf weed killer to be at its most effective, the target plant — in our case, dandelions — must have a good foliage surface area to absorb the herbicide. To facilitate this, I recommend you do not mow your lawn for 5 days prior to applying the weed killer.

This allows sufficient time for the dandelion plants to put out new foliage and provide an adequate surface area for the spray to settle on. Allow 24 hours or more for the systemic herbicide to be absorbed via the plant’s leaves. I would not mow the lawn for another 48 hours afterward.

Furthermore, cutting your grass will weaken the grass blades themselves. Freshly cut grass may be more susceptible to damage even from lawn-safe, selective herbicides. A 5-day grace period between cutting the grass and spraying your dandelions will allow the lawn to recoup and be in good condition ahead of spraying.

What Can I Spray In My Yard To Kill Dandelions?

There are many good weed killers on the market for treating broadleaf weeds such as dandelions, clover, spurge, and other common weeds. You can choose between a selective or non-selective spray that contains pre-emergent and/or post-emergent herbicides.

Non-Selective Herbicide

Generally, non-selective herbicides are used for general use around your yard but are not to be used on lawns. Non-selective active ingredients commonly include:

  • Diquat
  • Flufenacet
  • Glyphosate
  • Mecoprop-P

Selective Herbicide

Selective herbicides target specific weeds or groups of weeds while preventing damage to other foliage, including turf grass. Selective dandelion weed killers can differentiate between your lawn and crabgrass. Selective herbicides include the following active ingredients:

  • 2, 4-D
  • Dicamba
  • MCPA
  • Clopyralid
  • Fluroxypry

There are many high-quality products readily available on the market. Choose from a ready-to-use formula or a concentrate.


    A pre-emergent weed killer is applied to the lawn in late fall or early winter and sits on the ground ready to eliminate any broadleaf weeds that germinate the following spring. If you look out for a fall pre-emergent lawn treatment, there are plenty of options on the market.


    A post-emergent can be applied in late spring or throughout the growing season when weeds are active. Post-emergent sprays kill existing weeds but typically won’t affect seeds in the soil.

    What Will Kill Dandelions But Not Grass?

    You can use natural organic substances with cornmeal as the active ingredient. Most are intended for application in the fall. Alternatively, opt for a lawn-specific selective herbicide that is designed to target broadleaf weeds such as dandelions.

    Final Thoughts On Spraying For Dandelions

    Hopefully, this overview gave you some form of clarity as to the best time to spray dandelions. For the best results, focus your efforts around the time of flowering but before the flower heads go to seed. Choose a time of day when the ground and dandelion foliage is dry to prevent herbicide run-off and dilution.

    Use your backpack sprayer to spray close to the weed and avoid wind drift causing the misapplication of the weed killer. Most importantly, select the correct herbicide for general use or use on the lawn.