How To Apply Weed Killer To Lawn Safely & Effectively

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Can you apply weed killer when it’s hot? No, you should avoid applying weed killer when temperatures are too high, generally above 85°F (29°C), as this can damage your lawn. Applying weed killer safely and effectively is key to a healthy, green yard. This guide will walk you through the best practices for weed control for lawns, ensuring your efforts pay off without harming your grass or the environment.

Preparing for Weed Control

Before you even think about reaching for that bottle of weed killer, proper preparation is essential. This means knowing your enemy (the weeds) and your ally (your grass), and choosing the right tools and time.

Identifying Your Weeds

Different weeds require different approaches. Some common lawn invaders include dandelions, clover, and crabgrass. Knowing what you’re dealing with will help you select the most effective weed killer.

Broadleaf Weeds: These typically have wider leaves than grasses and often have taproots. Dandelions, clover, and plantain fall into this category.
Grassy Weeds: These look like grass but are often undesirable, such as crabgrass, foxtail, and nutsedge.

Choosing the Right Weed Killer

There are several types of weed killers available. The choice depends on your target weeds and whether you want to prevent or kill existing weeds.

Selective Herbicides: These target specific types of plants, usually broadleaf weeds, while leaving grasses unharmed. This is ideal for general lawn care.
Non-Selective Herbicides: These kill all plants they come into contact with. They are useful for clearing areas before planting or for tough, invasive weeds, but use them with extreme caution on an established lawn.
Pre-Emergent Herbicides: Applied before weed seeds germinate, these prevent new weeds from growing. A crabgrass preventer application is a common example.
Post-Emergent Herbicides: These are designed to kill weeds that have already emerged. You’ll find many dandelion killer application products in this category.

Gathering Your Supplies

To ensure safe weed killer application, you’ll need a few key items:

Weed Killer: Choose the appropriate type for your needs.
Sprayer: This could be a handheld pump sprayer, a backpack sprayer, or a hose-end sprayer. Ensure it’s clean and in good working order.
Personal Protective Equipment (PPE): This is crucial for safe weed killer application. Wear long sleeves, long pants, chemical-resistant gloves, and eye protection.
Measuring Tools: Cups and spoons for accurate mixing.
Water Source: For mixing and rinsing.
Stirring Stick: If mixing granular products.

Best Time to Apply Weed Killer

Timing is critical for success. Applying weed killer at the wrong time can reduce its effectiveness or even damage your lawn.

Weather Conditions Matter

Temperature: As mentioned, avoid applying when temperatures are consistently above 85°F (29°C). Heat can cause the weed killer to evaporate too quickly, making it less effective, and can stress your lawn, leading to browning. Cool-season grasses are particularly susceptible to heat damage from herbicides.
Rain: Do not apply weed killer if rain is expected within 24 hours. Rain can wash the herbicide off the weeds before it can be absorbed. Conversely, if you apply it and it rains too soon, it can dilute the product.
Wind: High winds can cause the spray to drift onto desirable plants, causing damage. It’s best to apply on a calm day.

Growth Stages of Weeds and Grass

Weed Growth: Post-emergent herbicides are most effective when weeds are actively growing and are young. Mature, established weeds can be more resistant.
Grass Growth: Healthy, actively growing grass is better able to recover from any potential stress caused by herbicides. Avoid applying to grass that is dormant or stressed from drought or extreme heat.

Seasonal Considerations

Spring: This is an excellent time for a crabgrass preventer application, as it targets the seeds before they sprout. It’s also a good time to tackle early emerging broadleaf weeds.
Fall: Many experts consider fall the best time for broadleaf weed control. Weeds are still actively growing and absorbing nutrients before winter, and they are preparing to store energy in their roots. Applying a dandelion killer application in the fall can be very effective. Fall applications also help reduce the weed seed bank for the following year.

Weed Killer Application Methods

There are several ways to apply weed killer, each with its pros and cons. The best method depends on the size of your lawn, the types of weeds, and your personal preference.

Spot Treating Weeds

This is a highly effective and economical method for smaller lawns or when you only have a few scattered weeds.

How to spot treat weeds:

Identify the Weed: Locate the specific weed you want to eliminate.
Mix the Herbicide: Follow the product label instructions carefully for mixing ratios.
Apply Directly: Using a sprayer (a small garden sprayer or even a paint brush for very small areas), apply the weed killer directly to the weed’s leaves. Aim to cover the foliage thoroughly.
Avoid Overlap: Be careful not to spray the surrounding grass, especially if using a non-selective herbicide.
Repeat if Necessary: For stubborn weeds, a second application might be needed after a week or two.

Advantages of Spot Treating:

Economical: Uses less product, saving money.
Environmentally Friendly: Reduces the amount of chemicals released into the environment.
Precise: Minimizes the risk of damaging non-target plants.

Disadvantages of Spot Treating:

Time-Consuming: Can take longer for larger areas with many weeds.
Requires Vigilance: You need to be actively looking for weeds.

Broadcast Application of Herbicides

This method involves applying the weed killer over the entire lawn. It’s more efficient for larger areas with widespread weed problems.

Types of Broadcast Application:

Granular Herbicides: These are mixed with fertilizer and spread using a broadcast spreader (either a walk-behind or handheld model). The granules are then activated by watering them into the soil.
- How to apply granular weed killer:
  1. Calibrate Your Spreader: Ensure the spreader is set to the correct rate according to the product label. This is crucial for even application.
  2. Apply Evenly: Walk at a consistent pace, overlapping your passes slightly to avoid streaks or missed spots.
  3. Water After Application: Unless the product specifies otherwise, water the lawn lightly to activate the granules.
Liquid Herbicides (Sprayed): These are applied using a sprayer, either a hose-end sprayer that attaches to your garden hose or a pump/backpack sprayer for more controlled application.
- How to spray weed killer evenly:
  1. Calibrate Your Sprayer: Similar to granulars, ensure your sprayer is set to the correct application rate. Many hose-end sprayers have settings on the dial. For pump sprayers, you’ll need to calculate your application rate based on how much area a tankful covers.
  2. Apply in Sections: Divide your lawn into manageable sections.
  3. Walk at a Consistent Pace: Move at a steady speed, sweeping the spray wand back and forth in an even pattern.
  4. Overlap Passes: Slightly overlap each pass to ensure complete coverage and avoid striping.
  5. Avoid Edges: Be careful near garden beds or desirable plants. Consider using a shield or carefully directing the spray away from them.

Advantages of Broadcast Application:

Efficient: Covers large areas quickly.
Uniform Coverage: Can provide consistent weed control across the entire lawn.

Disadvantages of Broadcast Application:

Uses More Product: Can be more expensive, especially if weeds are sparse.
Higher Risk of Over-Application: Requires careful calibration to avoid damaging the lawn or over-saturating areas.
Potential for Drift: Liquid sprays can drift if there’s wind.

Applying Herbicides Correctly: Step-by-Step

Accurate application is paramount for both effectiveness and safety. Always read and follow the product label.

Step 1: Read the Label

This is the most important step. The label contains vital information on:

Target weeds.
When and how to apply.
Mixing instructions and rates.
Safety precautions and required PPE.
Restrictions (e.g., temperature, rain, watering).
Re-entry times for people and pets.

Step 2: Mix the Weed Killer (If Applicable)

Liquid Concentrates: Measure the concentrate accurately using a dedicated measuring cup. Add the specified amount of water to your sprayer.
Granular Products: Follow the spreader settings on the label. Do not add water unless instructed.

Step 3: Prepare Your Sprayer

Cleanliness: Ensure your sprayer is clean. If it has been used for other chemicals, rinse it thoroughly multiple times to prevent contamination.
Nozzle Check: Make sure the nozzle is clean and working properly to ensure an even spray pattern.

Step 4: Apply the Weed Killer

Choose Your Method: Decide whether spot treating or broadcast application is best.
Coverage: Aim for even coverage. For liquids, you want to coat the weed’s leaves. For granulars, even distribution on the soil surface is key.
Direction: Spray with the wind, not against it, to minimize drift.

Step 5: Clean Up and Storage

Rinse Sprayer: Immediately after use, rinse your sprayer thoroughly with water. Dispose of the rinse water properly (e.g., on an untreated grassy area away from water sources).
Clean Equipment: Wash any measuring cups or tools used.
Store Safely: Store weed killer in its original container, in a cool, dry, locked place, away from children and pets.

Specific Weed Killer Applications

Let’s delve into some common weed control scenarios.

Dandelion Killer Application

Dandelions are tough, with deep taproots.

Timing: The best time for a dandelion killer application is when they are actively growing and before they go to seed. Fall is particularly effective for targeting the root system.
Method: Spot treatment is often ideal for dandelions, especially if they are few. If your lawn is heavily infested, broadcast application might be necessary. Look for herbicides specifically labeled for dandelion control.
Key: Ensure the herbicide reaches the root. Some products work on contact, while others are systemic and are absorbed by the leaves and translocated to the roots.

Crabgrass Preventer Application

Crabgrass is an annual grassy weed that germinates in the spring when soil temperatures reach around 55-60°F (13-16°C).

Timing: A crabgrass preventer application is crucial in early spring, before the crabgrass seeds have a chance to germinate. This is often around the time when forsythias bloom.
Method: This is typically a broadcast application. You can find products that are pre-emergent only or combination products that also contain fertilizer.
Key: Do not apply a crabgrass preventer if you plan to seed your lawn soon, as it will also prevent grass seed from germinating. Always check the label for seeding restrictions. If you miss the pre-emergent window, post-emergent crabgrass killers are available, but they are generally less effective and can be harder on your lawn.

Safe Weed Killer Application Practices

Prioritizing safety ensures you and your family, including pets, are protected.

Personal Protective Equipment (PPE)

Gloves: Wear chemical-resistant gloves (nitrile or rubber) to protect your skin from contact.
Eye Protection: Safety glasses or goggles will prevent accidental splashes from entering your eyes.
Clothing: Long-sleeved shirts and long pants create a barrier.
Footwear: Closed-toe shoes are a must.

Protecting Your Lawn and Garden Beds

Avoid Overlap: When spraying, walk at a consistent pace and overlap your passes slightly. This prevents over-application and potential damage to your grass.
Shield Sensitive Plants: If spot treating near desirable plants or flower beds, use a piece of cardboard or plastic to shield them from the spray.
Hose-End Sprayer Guards: Some hose-end sprayers come with shields to help direct the spray downward.

Protecting Pets and Children

Keep Them Away: Ensure pets and children are not in the yard during application and until the spray has dried completely.
Read Re-Entry Times: The product label will specify when it is safe for people and pets to re-enter the treated area. This is typically after the spray has dried.

Environmental Safety

Water Sources: Never apply weed killer near wells, streams, ponds, or other water bodies.
Proper Disposal: Dispose of empty containers and leftover product according to local regulations. Never pour excess weed killer down a drain or into the environment.
Beneficial Insects: Be aware that some herbicides can harm beneficial insects. Applying only when needed and spot treating can help minimize this impact.

Troubleshooting Common Issues

Even with careful application, you might encounter some problems.

Weeds Not Dying

Incorrect Dosage: You may have used too little product.
Wrong Product: The herbicide might not be effective against the specific weed.
Washed Away: Rain may have washed the product off too soon.
Weeds Too Mature: Older weeds can be harder to kill.
Application Too Early/Late: Timing can impact effectiveness.

Lawn Damage (Browning, Yellowing)

Over-Application: Too much herbicide was used, or it was applied too frequently.
Wrong Product: The herbicide may be too harsh for your type of grass.
Temperature Stress: Applied in hot weather.
Drift: Spray drifted onto desirable grass.

Maintaining a Weed-Free Lawn

Weed control is an ongoing process. Consistent care will keep your lawn looking its best.

Regular Mowing

Proper Height: Mow your lawn at the recommended height for your grass type. Taller grass shades out weed seeds and discourages germination.
Sharp Blades: Ensure your mower blades are sharp. Dull blades tear grass, making it susceptible to disease and weeds.

Proper Watering

Deep and Infrequent: Water your lawn deeply but less often. This encourages deep root growth, making your grass more resilient.
Avoid Overwatering: Overwatering can create conditions favorable for some weeds and fungal diseases.

Fertilization

Healthy Grass: A well-fed, healthy lawn is your best defense against weeds. It can outcompete them for resources like sunlight, water, and nutrients.
Choose Wisely: Use a balanced fertilizer appropriate for your grass type and the season.

Aeration and Dethatching

Improve Soil Health: Aerating and dethatching your lawn improve air circulation, water penetration, and nutrient uptake, all of which contribute to a healthier, more robust turf that can resist weeds.

Frequently Asked Questions (FAQ)

Q1: Can I apply weed killer when it’s raining?
A1: No, it’s best to avoid applying weed killer if rain is expected within 24 hours, as the rain can wash the product away before it takes effect.

Q2: How long should I wait before mowing after applying weed killer?
A2: Generally, wait at least 24-48 hours after applying liquid weed killer before mowing. For granular products, follow the label instructions, which may vary. Mowing too soon can remove the weeds before they fully absorb the herbicide.

Q3: Is it safe to let my dog on the lawn after applying weed killer?
A3: No, keep pets off the lawn until the spray has dried completely. Always check the product label for specific re-entry times for pets and children.

Q4: What’s the difference between pre-emergent and post-emergent weed killers?
A4: Pre-emergent weed killers are applied before weed seeds germinate to prevent them from growing. Post-emergent weed killers are applied to kill weeds that have already emerged.

Q5: My lawn has a lot of dandelions. What’s the best way to get rid of them?
A5: For dandelions, a targeted dandelion killer application is recommended. Spot treating individual weeds is effective, especially in fall when they are storing energy in their roots. Ensure the product you use is labeled for dandelion control.

By following these guidelines, you can achieve effective weed control for your lawn while ensuring the safety of your family, pets, and the environment. Happy mowing!