Landscape Fabric Calculator

Rolls by Bed Size

Landscape fabric is sold in rolls of fixed width and length, so you calculate by total square footage. Find the bed area, add 10 to 15 percent for overlap and waste, then divide by the roll coverage. A 20 x 15 ft bed is 300 square feet, which becomes 345 square feet with the 15 percent buffer, needing about two 3 ft by 100 ft rolls. Rolls come in 3, 4, 6, 12.5, and 15 foot widths. A 3 ft by 100 ft roll covers 300 square feet, and a 4 ft by 300 ft roll covers 1,200 square feet. The calculator handles the buffer and roll math for you.

Overlap Allowance

Fabric seams must overlap so weeds and light cannot slip through the gaps. The standard overlap is 6 to 12 inches at every seam. High-weed-pressure beds use the wider 8 to 12 inch overlap. This overlap is why you add a 10 to 15 percent waste factor to the raw square footage before buying rolls. Without the buffer, you run short at the last seam. Pin the overlaps with staples every 1 to 2 feet so the seams stay sealed. A 300 square foot bed needs roughly 50 to 80 staples along the edges and seams.

Fabric Under Mulch - Yes or No?

Landscape fabric works well under rock and gravel but is debated under organic mulch. Under rock, the fabric keeps stone from sinking into the soil and blocks weeds for years, so the National Association of Landscape Professionals (NALP) treats it as standard for decorative stone. Under wood mulch, the case is weaker. Organic mulch breaks down into a thin soil layer on top of the fabric, and weeds root in that layer anyway. The fabric also blocks the mulch from feeding the soil below. For wood mulch beds, many gardeners skip the fabric and rely on 3 inches of mulch for weed control.

What grade of landscape fabric should I buy?

Buy commercial-grade woven fabric for permanent rock installations and beds you will not disturb. Woven fabric rated for 20 plus years resists tearing and lasts under stone. Lighter spun or non-woven fabric suits temporary or low-traffic beds. Avoid thin plastic sheeting, which blocks water and air to the roots. Match the grade to the job: heavy woven under rock, lighter fabric under occasional-replant beds.

How do I install landscape fabric?

Clear the bed of weeds and rake it smooth. Roll out the fabric and overlap each seam by 6 to 12 inches. Pin the edges and seams with staples every 1 to 2 feet. Cut X-shaped slits to plant through the fabric. Cover with 2 to 3 inches of mulch or rock so sunlight does not degrade the fabric. Keep the overlaps tight so weeds cannot push through the seams.

Pros and Cons of Landscape Fabric

Landscape fabric has clear strengths and real drawbacks. On the plus side, it blocks weeds for years under rock, keeps stone from sinking into the soil, and separates materials cleanly. It works best in permanent installations you will not replant. On the downside, it can block water and air to the soil if you choose a non-permeable grade, and organic matter builds up on top over time and grows weeds anyway.

The fabric is right for some jobs and wrong for others. Use it under decorative rock, gravel paths, and around hardscape where nothing will be replanted. Skip it in active garden beds and under organic wood mulch, where it gets in the way of replanting and the breaking-down mulch defeats it. When you do use fabric, choose a permeable woven grade so water still reaches the roots, and overlap the seams 6 to 12 inches so weeds cannot push through the gaps.

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