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 and settle, ready to germinate and start the cycle again.

That is why you need to act as soon as you can and 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 by understanding the best time to spray dandelions for maximum impact.

When Should You Spray Dandelions?

The dandelion plant is at its weakest after blooming, so this is the ideal time to apply an herbicide spray. The challenge is catching the plant after flowering but before releasing its seeds.

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 and the final flowering period will be 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.

So, although it is best to spray dandelions after blooming when they are weak, the argument against this approach is that the damage is done, and the seeds may have traveled on the wind ready to germinate.

Based on this I would recommend spraying each weed as soon as you see clear signs of active plant growth, and I like to get ahead of blooming with a view on reducing the overall dandelion seed density within the garden.

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 Climate

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 at the hottest part of the day the water particles can evaporate too fast preventing optimal absorption and in fact, cause scorching and drying of the broad leaves.

The opposite applies in cooler cold climates or seasons.

Cool Climate

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

What Is The Best Temperature To Spray Weeds?

It is generally best to spray weeds when temperatures are above 60 degrees Fahrenheit when the plants are actively growing. Be sure to check no rain is forecast and spray when the foliage is dry but avoid applying 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 the leaf. As a systemic herbicide the active ingredients need to be absorbed through the foliage, so it is best applied when the dandelion foliage is dry.

Spray Dandelions on a Calm day

Depending on the type of herbicide you are spraying you may be at risk of misapplied weed killer spray being carried on the wind to nearby plants or water features. So, I would always avoid spraying on a windy day and instead wait until you have calm, still conditions.

Fill your backpack sprayer with your chosen herbicide concentrate or use 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 the 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 requires the target plant, in our case dandelions, to 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 will allow sufficient time for the dandelion plants to put out new foliage to offer a good contact 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 and they are susceptible to damage even from lawn-safe selective herbicides. So, the 5 days 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 herbicide spray.

Non-Selective Herbicide

Generally, selective herbicides are used for general use around your yard but are not to be used on lawns. The active ingredient commonly used include:

  • Diquat
  • Flufenacet
  • Glyphosate
  • Mecoprop-P

High performing non-selective herbicides include:

What Will Kill Dandelions But Not Grass?

You can use natural organic substances such as Espoma Organic Weed Preventer, whose active ingredient is Corn Meal and is intended for application in fall, or you can opt to use a lawn-specific selective herbicide that is designed to target broadleaf weeds such as dandelions.

Selective Herbicide

Selective herbicides will target specific weeds or groups of weeds and prevent damage to other foliage such as grass or more specifically lawn. Selective dadelion 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 in ready-to-use form or concentrates for dilution. Some of the best include:

These products come in spray form and contain either pre-emergent or post-emergent herbicides.


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 lookout 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.

Best Time To Spray Dandelions Final Thoughts

Hopefully this overview will give you some form of clarity as to the best time to spray dandelions. In summary, 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 and free from moisture 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.