Mulching & Other Methods for Weed Control

Prepared by: L. Robert Barber, Frank Cruz, & Ilene Iriarte

For: Guam Cooperative Extension Service & Guam

Department of Agriculture

Funding provided by: United States Department of Agriculture Natural Resources Conservation Service, Western Region Sustainable Agriculture Research and Education,

Administration for Native Americans,, & Sanctuary Incorporated

What is a weed?

• Plant growing out of place• A plant can be desirable in one

situation and be a pest in another– Can be fast growing– Often produces a lot of seeds or has

persistent roots

How Weeds Harm Desirable Plants

• Competes for water, nutrients, light, and space

• Harbors pests and diseases• Can release toxins into the soil

Weed Management

• The best time to begin an effective weed management program is before planting

• Proper site preparation can reduce weed problems

• Monitor frequently for weeds• Remove weeds while they’re seedlings• Maintain a directed low volume irrigation

system• Minimize disturbances in the soil• Correctly maintain mulch

Weed Control Practices

• Mechanical – Hoeing/Hand weeding– Plowing, harrowing, cultivating, other

tillage

• Fire/Propane Burner• Mowing/Bush cutting• Ground Cover – Living Mulches• Chicken Tractor• Mulching

Mechanical Weeding - Cultivation

• Labor, equipment and energy intensive• Bare soil more susceptible to erosion• Frequent tillage speeds organic matter

decomposition.• Brings buried seeds to the surface

– Cultivate once germinated

• Plant spacing must allow for equipment

Fire

• Fire can be used to remove weeds in a big area– Burns the organic matter– Leaves soil bear and high chance of

erosion

• Propane Burner is used for spot treatments– Must be careful

Mowing & Bush cutting

• Benefits of maintaining a living cover and mowing or bush cutting– May reduce competition– Can help prevent soil erosion

• Disadvantages:– Often damages desired plants – Physically harms plants – Bush cutter

disease (careless cuts girdle tree) kills huge numbers of trees on Guam.

Ground Covers or Living Mulches

• Can be natural cover developed by frequent mowing, or can be planned planting like sweet potato or perennial peanut or other cover crop.

• Benefits– Prevents germination of weed seeds– Prevents soil erosion– Insulates soil– May add nitrogen to soil (ex. Perennial peanut)– Attractive

• Disadvantages– Can provide a habitat for pests– Can compete for water & nutrients

Chicken Tractor

• Mobile Pens• Weeding• Pest Control• Fertilizer• Food

Types of Mulch

• Two types of mulch; Organic & Inorganic

• Inorganic Mulch (Plastic sheets):– Does not decompose– Non-living– May prevent water loss, soil protection,

increase absorption– Does not improve soil or add nutrients– Good for walk ways, and paths

Benefits of Mulch

• Conserves water & reduces erosion• Improves soil structure, & absorption• Adds nutrients• Suppress weed growth• Prevents pathogens from splashing on foliage• Insulates soil• Increases microorganisms, earthworms, &

insects• Prevents trunk damage from bush cutter

– Limits weeds near plant so no need to cut close to plant

• Reduces landscape maintenance

Organic Mulch

• Organic Mulch:– Living Materials– Categorized by size; Fine or Coarse

Material– Fine Material:

• A lot of surface area• Can suffocate plants

– Coarse Material:• Doesn’t blow away as easily• Water & air can penetrate through

Organic Mulch

• Examples of Organic Mulch:– Grass clippings, small leaves*– Wood chips**– Pine needles (Gago Tree)**– Banana leaves & Palm fronds**– Coconut husks**– Branches**– Compost– Shredded paper*

*Fine Material & ** Coarse Material

What is in a Mulch

• Decaying organic material• Undecomposed compost• Applied to surface of the soil over time

blends with the soil• Consists of:

– Nutrients– Leaves– Branches– Microorganisms– Insects

Palm fronds around breadfruit tree

Now That You Have Mulch

• Apply in planting beds• Around established trees, & newly

planted trees• Mulch will eventually need replacing• Fine material need to be replaced

often• Coarse material can be replaced

either once a year to every two years

Mulched Raised Bed

Bed mulched with pine needles (Gago tree)

How To Apply Mulch

• Leave a 3-6” gap from the base of the plant to mulch

• For individual trees:– Make a circle that is 2’ in diameter for

every inch of trunk diameter– Increase size as tree gets bigger

• For planting beds:– Mulch entire bed

Undesirable - Mulch up Against Trunk

How Much to Apply

• Thickness depends on types of material

• Fine Material:– No thicker than 2 – 3 inches– Can mat together & suffocate plants

• Coarse Material:– At least 4 inches– Thinner weeds can penetrate through if

too thin a layer.

Possible Problems

• Mulch can turn “sour”– Air was not allowed to penetrate

through

– Toxic substances are produced

– Plants drop leaves, turn yellow, and can die

– Smells like sulfur, vinegar, or ammonia

Wire Chicken Barrier

Possible Problems

• Chickens and Pigs love it too– Can destroy plants, dig up roots

– Scatter mulch

– Where animals are a pest, create a barrier