Should I Put Cardboard Under Mulch?

When It Makes Sense

• Good fit: New garden beds where you want to suppress existing weeds without chemicals and you have access to clean, untreated cardboard.
• Good fit: Landscapes with low‑maintenance perennials where a biodegradable barrier can break down over a season, adding organic matter.

When You Should Avoid It

• Warning sign: Areas prone to excess moisture or poor drainage, as cardboard can trap water and promote rot around plant roots.
• Warning sign: Beds where you plan to plant moisture‑sensitive seedlings or annuals that need frequent soil disturbance.

Pros and Cons

Pros

• Provides an inexpensive, biodegradable weed barrier that eventually becomes part of the soil.
• Improves mulching efficiency by reducing the amount of mulch needed to cover the soil surface.

Cons

• Can retain water, leading to damp conditions that may harm root systems in poorly draining soils.
• Requires proper layering and overlap; improper installation may cause gaps where weeds still emerge.

Decision Checklist

• Is the soil well‑draining, or will you add drainage measures if you use cardboard?
• Do you have access to clean, corrugated cardboard without glossy or waxed coatings?
• Are you prepared to monitor the bed for any signs of waterlogging or cardboard degradation?

Alternatives to Consider

Instead of cardboard, you can use landscape fabric, newspaper layers, or a thicker organic mulch alone. For raised beds, a layer of compost followed by mulch may provide similar weed suppression without the risk of water retention.

Final Recommendation

Cardboard under mulch works well for established beds with good drainage and low‑maintenance plantings. If your garden struggles with moisture or you need frequent soil access, opt for a more permeable barrier or rely on mulch alone. When in doubt, consult a horticulture professional to evaluate site‑specific conditions.