Can You Use Preemergence Herbicide Around Trees and Shrubs?

Maintaining a healthy landscape often involves controlling weeds, which can compete with desirable plants for nutrients, water, and sunlight. One popular method for managing weeds is the application of preemergence herbicides. These products prevent weed seeds from germinating and establishing themselves in your garden or lawn. However, when it comes to using preemergence herbicides around trees and shrubs, many gardeners and landscapers are cautious. This article explores whether you can safely apply preemergence herbicide around trees and shrubs, what considerations to keep in mind, and best practices for effective weed control without harming your valuable plants.

What Is Preemergence Herbicide?

Preemergence herbicides are chemical substances applied to the soil surface before weed seeds germinate. Unlike postemergence herbicides that kill actively growing weeds, preemergence herbicides work by inhibiting seed germination or killing young seedlings shortly after they sprout.

Common preemergence herbicides include:

• Pendimethalin
• Dithiopyr
• Prodiamine
• Oryzalin

These products create a chemical barrier in the soil that disrupts cell division or root growth in emerging weed seedlings.

Why Use Preemergence Herbicides?

Weeds pose several challenges in a landscape:

• Compete for nutrients, water, and light
• Harbor pests and diseases
• Mar the aesthetic appeal of garden beds and lawns
• Require frequent manual removal or repeated herbicide applications

Using preemergence herbicides is an efficient way to reduce the number of weeds before they appear. They help maintain clean planting areas with less effort compared to postemergent weed control.

Concerns About Using Preemergence Herbicide Near Trees and Shrubs

While preemergence herbicides are effective weed management tools, many gardeners hesitate to apply them close to trees and shrubs due to concerns about phytotoxicity (chemical injury) to these plants.

Potential Risks

1. Root Damage: Many trees and shrubs have shallow root systems near the soil surface. If an herbicide interferes with root growth or function, it can stress or damage these plants.
2. Chemical Uptake: Some herbicides can be absorbed by tree roots or bark tissue, leading to toxicity symptoms such as leaf discoloration, wilting, or dieback.
3. Soil Microorganism Impact: Herbicides can alter soil microbial communities crucial for nutrient cycling and plant health.
4. Non-target Effects: Drift or misapplication may unintentionally affect nearby sensitive ornamentals.

Factors Influencing Safety

Whether a preemergence herbicide is safe depends on:

• The specific active ingredient
• The concentration and application rate
• The plant species involved (some are more sensitive)
• Soil type and moisture conditions
• Timing of application (seasonal vulnerability)

Understanding these factors helps inform safe usage.

Are Preemergence Herbicides Safe Around Trees and Shrubs?

The answer is: It depends — on the herbicide type, application method, tree/shrub species, and timing.

Generally Considered Safe Herbicides

Certain preemergent chemicals have been shown to be safe for use around established trees and shrubs when applied according to label instructions:

• Pendimethalin: Often recommended for ornamental beds; low uptake by woody plants.
• Dithiopyr: Provides good grass weed control; relatively low risk for tree roots.
• Prodiamine: Effective on many weeds; generally safe when not overapplied.

Manufacturers typically provide detailed usage guidelines that specify which ornamental plants tolerate their products.

Species Sensitivities

Some woody plants are more sensitive than others:

• Sensitive: Azaleas, ferns, dogwoods, magnolias
• Tolerant: Pines, junipers, oaks (generally more robust)

Always consult extension service recommendations or product labels for guidance on specific species.

Application Timing

Applying preemergence herbicide during periods when trees and shrubs are actively growing new roots increases risk. Late fall or early spring applications when root activity is minimal reduce potential injury.

Best Practices for Using Preemergence Herbicide Around Trees and Shrubs

To safely use preemergent herbicides without damaging your trees and shrubs, follow these strategies:

1. Read Product Labels Carefully

Herbicide labels contain critical information about:

• Safe distances from tree trunks or shrub bases
• Permitted plant types
• Maximum application rates
• Reentry intervals
• Environmental warnings

Labels are legal documents—always comply fully.

2. Use a Targeted Application Method

Avoid broadcasting the herbicide over wide areas where established woody plants grow. Instead:

• Apply to bare soil areas away from the dripline (the outer edge of the canopy)
• Use shielded sprayers or wiper applicators to limit overspray
• Avoid treating areas with mulch too close to tree trunks since herbicides may concentrate there

3. Maintain Mulch Barriers

A thick layer of organic mulch around trees and shrubs suppresses weeds naturally by blocking sunlight to seeds. Using mulch reduces reliance on chemical controls within the root zone.

4. Adjust Application Rate

Use the minimum effective dose necessary to control weeds. Overapplication increases risk of damage.

5. Water In Properly

Most preemergent herbicides require watering in shortly after application to move the chemical into the soil profile where seeds germinate.

Avoid excessive irrigation that could move chemicals toward roots.

6. Avoid Application Before Planting or During Transplant Stress

Newly planted trees/shrubs have delicate root systems highly vulnerable to chemical injury. Wait until plants are well-established before applying preemergents nearby.

7. Monitor Your Plants After Application

Check regularly for signs of stress such as yellowing leaves, wilting, or dieback. Early detection allows corrective action like additional watering or stopping further applications.

Alternatives to Preemergence Herbicides Around Trees and Shrubs

If you prefer not to use chemical controls near sensitive plants, consider these options:

• Manual Weeding: Regular hand-pulling reduces weed pressure without risk.
• Mulching: A thick mulch layer suppresses most seed germination naturally.
• Landscape Fabric: Placing geotextile fabric beneath mulch limits weed emergence.
• Postemergence Spot Treatment: Use selective postemergent herbicides carefully applied only on visible weeds.

Combining cultural practices with minimal chemical use often provides sustainable long-term control.

Conclusion

Preemergence herbicides can be used around trees and shrubs under proper conditions but must be applied carefully based on the specific product’s instructions and plant sensitivities. Understanding how these chemicals work and following best practices like targeted applications, correct timing, mulching, and monitoring will help protect your valuable woody plants from harm while effectively controlling weeds.

When in doubt, consult local extension services or a professional arborist/landscaper familiar with your region’s plant species and environmental conditions before applying any herbicidal treatments near trees and shrubs. By balancing effective weed management with thoughtful care for your landscape’s health, you can achieve beautiful gardens free of invasive weeds without sacrificing the vitality of your trees and shrubs.