Measure the top of the finished hay stack, then add overhang on all sides. Cover the top to shed rain and leave the sides open so the stack can breathe. Fully wrapping a stack is rarely the best default.
Hay covers are agricultural weather tools. The goal is dry tops and moving air, not a sealed plastic bag around the forage.
Cover the top first
Rain enters most stacks from above. Side exposure matters, but airtight side curtains can trap moisture and heat. For many outdoor stacks, a well-secured top sheet is the highest-value cover.
Measure the stack, not the field
- Build or mark the final stack footprint.
- Measure top length and top width.
- Add overhang for water drip clear of the outer bales.
- Plan anchor points that will not tear bales apart or create trip hazards.
Worked example
A rectangular stack top measures 20 × 40 ft. With 2 ft of overhang on every side, the planning cover is about 24 × 44 ft. If the only stock option is 25 × 45 or 30 × 50, choose the size you can still handle and secure. A cover that is technically big enough but too heavy to tension will fail in the first storm.
Material options
- Heavy PE farm tarps: common, affordable, easy to source
- Coated industrial fabric: tougher for repeated seasonal use
- Billboard vinyl / reused vinyl: sometimes used as low-cost heavy covers
Field tips
- Create a slight crown so water runs off.
- Retension after the first rain and wind event.
- Inspect chafe points where rope crosses bale edges.
- Do not assume any tarp makes wet hay safe to store.
Frequently asked questions
Should hay be fully wrapped in a tarp?
Usually no for drying or breathing stacks. Cover the top to shed rain and leave sides open for airflow. Fully wrapping wet or green hay can trap moisture and increase spoilage risk.
How much overhang does a hay tarp need?
Enough to carry water past the outer bales without turning into full side curtains. Many stacks work with 1 to 3 ft of overhang, depending on stack height and wind.
Can billboard vinyl be used as a hay tarp?
Some farms reuse billboard vinyl as a heavy, low-cost top cover. It can work, but check grommet placement, weight, and whether the sheet can be handled safely when wet.
What size tarp covers a standard round-bale stack?
It depends on how many bales wide and long the stack is. Measure the top footprint of the finished stack, then add overhang. Do not buy from bale count alone.
How do I stop a hay tarp from blowing off?
Use a ridge or slight slope, secure all sides, and add intermediate tie points. Sandbags, ratchet straps, or anchored ropes work better than a few loose corners.
How this guide was prepared
We separate geometry and unit conversions from product claims, use exact standards where available, and flag specifications that vary by manufacturer. See our editorial policy for the review process.