Pre-Emergent & Herbicide Timing Calculator

Get precise timing recommendations for pre-emergent and post-emergent herbicide applications. Find the optimal windows to control crabgrass, dandelions, and other weeds based on your location and grass type.

Targeted Weed Control

Get specific timing for crabgrass, dandelions, clover, and other common lawn weeds.

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Timing recommendations based on your specific climate and soil temperature patterns.

Urgency Indicators

Color-coded alerts show when timing is critical, optimal, or too late for applications.

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Weeds best controlled before they germinate
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Frequently Asked Questions
Common questions about herbicide timing and weed control

When should I apply pre-emergent herbicide for crabgrass?

Pre-emergent herbicides should be applied before soil temperatures reach 55°F for 3 consecutive days. This is typically in late winter to early spring, depending on your region. In northern areas, this might be March-April, while in southern areas it could be February-March.

How do I know if I'm too late for pre-emergent application?

If you can see crabgrass or other target weeds already growing, you're likely too late for pre-emergent control. However, you can still use post-emergent herbicides to control existing weeds. The key is applying post-emergent products when weeds are young and actively growing.

What's the difference between pre-emergent and post-emergent herbicides?

Pre-emergent herbicides prevent weed seeds from germinating and should be applied before weeds appear. Post-emergent herbicides kill existing weeds and should be applied when weeds are actively growing. Some products can be used for both purposes depending on timing and application method.

Can I apply herbicides in summer heat?

Summer application requires caution. Avoid applying during peak heat (above 85°F) as this can stress your grass and reduce herbicide effectiveness. Apply early morning or evening, ensure adequate soil moisture, and use products specifically labeled for summer application.

How long should I wait between herbicide applications?

Most herbicides require 2-4 weeks between applications. Check the product label for specific recommendations. For pre-emergent products, you typically apply once in spring and possibly once more in late summer for annual weeds that germinate later in the season.

What happens if it rains after I apply herbicide?

Light rain (less than 0.5 inches) within 24 hours can actually help activate granular pre-emergent herbicides. However, heavy rain can wash away the product before it has time to work. Check the product label for specific rainfastness information and reapply if necessary.

Are herbicides safe for my grass type?

Different grass types have varying tolerance to herbicides. Cool-season grasses like Kentucky Bluegrass and Tall Fescue are generally more tolerant, while warm-season grasses may have different requirements. Always check the product label for grass type compatibility before applying.

How do I choose between different herbicide products?

Consider your target weeds, grass type, application timing, and budget. Pre-emergent products are best for preventing weeds, while post-emergent products are for controlling existing weeds. Look for products specifically labeled for your target weeds and safe for your grass type.

When is the best time to treat dandelions and broadleaf weeds?

Broadleaf weeds like dandelions are best controlled in fall (September-October) or early spring (March-April) when they're actively growing but not flowering. Fall application is often most effective because the herbicide is transported to the roots as the plant prepares for winter.

How often should I apply pre-emergent herbicide?

Most pre-emergent herbicides provide 3-6 months of control. For annual weeds like crabgrass, one application in spring is usually sufficient. However, in areas with multiple weed germination periods, a second application in late summer may be needed for weeds that germinate later.