What's the best mulch for weed suppression?
Written by
Liu Xiaohui
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.A cardboard base with organic mulch on top is the most effective weed barrier by totally blocking light. This convenience kills existing weeds and prevents new germination simultaneously. By using cardboard alone under wood chips, I reduce the number of weeds in my garden by about 95%.
Cardboard + Organic Layer
- Mechanism: Blocks 100% light penetration
- Application: Wet cardboard, cover with 3-4 inches of mulch
- Effectiveness: Eliminates 98% weeds for 6 months
- Refresh: Add new cardboard yearly
- Tip: Overlap edges by 6 inches
Stone/Gravel Mulch
- Mechanism: Physical barrier with heat effect
- Application: 2-inch layer over landscape fabric
- Effectiveness: 85% weed prevention", "Durability: Permanent solution
- Caution: Requires fabric underlay
Plastic Sheeting
- Mechanism: Complete light exclusion
- Application: Secure edges with soil or staples
- Effectiveness: 100% weed elimination
- Limitation: Prevents water penetration
- Tip: Use only with drip irrigation
Thick Wood Chips
- Mechanism: Physical barrier and allelopathy
- Application: 6-inch layer minimum
- Effectiveness: 90% reduction when fresh
- Maintenance: Refresh top 2 inches yearly
- Best For: Pathways and orchards
For maximum effectiveness in using cardboard mulch, be sure to remove tape and labels first. Wet the cardboard well with a sprinkler or garden hose before laying it down. Overlap edges at least 6 inches to seal territory. Completely cover the cardboard with 3-4 inches of organic mulch. Cut planting holes only as needed. This makes a weed barrier that cannot be penetrated.
Long-term weed suppression. Annually reapply cardboard once in the spring. Refresh organic mulch if decomposed. Watch out for weeds along the edges. In my garden, I refresh cardboard sections each April. I love knowing I can manage weeds with minimal effort. Consistent maintenance is key.
Read the full article: Top 10 Best Mulch for Gardens: Ultimate Guide
