Silage Tarp Guide: Sizing, Weighting & Air Exclusion

Silage Tarp vs Hay Tarp: Key Difference

A hay tarp keeps rain off — see the Hay Tarp Buying Guide for hay-specific selection. A silage tarp must also exclude oxygen. Silage fermentation (the preservation process) is anaerobic — it requires the complete absence of oxygen. Any oxygen that enters causes aerobic spoilage (heating, mold, dry matter loss).

This means a silage tarp must:

1. Be completely airtight (no holes, tears, or gaps)
2. Be weighted continuously — every 3–4 ft across the entire surface
3. Be sealed at all edges with sand bags, rubber mats, or soil

Silage Tarp Sizing Formula

Tarp width  = bunker/pile width + (side overlap × 2)
Tarp length = bunker/pile length + (end overlap × 2)

Side overlap: How far the tarp extends beyond the pile on each side to seal against oxygen entry. Minimum: 2 ft. Recommended: 3–4 ft, tucked under a sand-bag row or buried in a soil berm.

For bunker silos (concrete walls): Tarp must extend from inside the wall on one side, over the top, and down to the ground or wall base on the other side, with extra sealing against the wall:

Tarp width = bunker interior width + (wall height × 2) + (floor overlap × 2)
Tarp length = silage pile length + 4 ft overlap each end

Sizing Example: Bunker Silo

Bunker: 80 ft long × 40 ft wide, walls 8 ft high, silage pile 10 ft high

Tarp width = 40 + (8 × 2) + (3 × 2) = 40 + 16 + 6 = 62 ft
Tarp length = 80 + (4 × 2) = 88 ft

Use a 62 × 88 ft tarp (custom) or two 40 × 50 ft tarps overlapping 6 ft at the center seam.

Silage Film Specifications

Silage films are different from general PE tarps:

Oxygen barrier (OB) films: Premium silage films with a co-extruded nylon or EVOH layer that greatly reduces oxygen transmission. For a full comparison of tarp materials including silage film, see the Tarp Types Guide. OB films reduce dry matter loss by 50–70% compared to standard PE film. The extra cost is typically recovered in first-season feed value savings on large silage piles.

Dry Matter Loss by Covering Method

On a 1,000-ton silage pile, reducing loss from 8% to 2% = 60 tons of saved silage. At $50/ton, that’s $3,000 saved per fill.

Weighting: The Most Critical Step

Silage tarps require continuous weighting across the entire surface — not just around the edges. Unweighted areas balloon from fermentation gas, breaking the air seal and allowing oxygen in.

Standard weighting:

• Tires (whole passenger car tires): every 3–4 ft in both directions across the entire surface
• Tire density: approximately 1 tire per 12–16 sq ft
• A 60 × 80 ft tarp (4,800 sq ft) needs 300–400 tires

Alternative weighting:

• Sand-filled bags: 50 lb bags placed 2 ft apart
• Gravel bags: Heavier and more stable in wind
• Tire sidewalls (cut tires): More irregular, cover surface well

Edges must be buried or weighted with continuous sand bags or rubber belting.

Sealing the Edges

Ground-level pile:

• Extend tarp 3–4 ft beyond the pile edge on all sides
• Lay 3–4 ft of tarp flat on the ground
• Cover that flat edge entirely with sand bags, tires, or a soil berm
• The tarp must not flap in wind — any movement breaks the seal

Bunker silo (concrete walls):

• Press tarp against the inside wall face and seal with foam backer rod or rubber strip
• Lay tarp over the wall top and weight on the outside with sand bags

Use the Tarp Size Calculator — select Hay / Silage Stack for pile dimensions, or use Flat Cover for a bunker silo floor footprint.

See also: Tarp Size Formula and Tarp Types Guide.