High Tunnels and Hoop Houses: What Season Extension Actually Costs and Why It Pays Off

A farmer I know in Ohio told me something that stuck: “My high tunnel cost $8,000 to build, and the first year it paid for itself in tomatoes alone.” He’s still farming in it five years later.

High tunnels, also called hoop houses or polytunnels, are the quiet workhorses of small and mid-size farms. They don’t get the attention that glass greenhouses or automated climate-control systems do, but they do something those expensive setups often can’t: they pay for themselves fast.

The premise is simple: an unheated, polyethylene-covered structure that traps solar heat during the day and releases it slowly at night. No furnace, no fans, no electricity. Just a frame, some plastic, and physics. The result is 4 to 8 extra weeks of growing on each end of your season. In colder regions, that gap is often the difference between a farm that survives winter and one that doesn’t.

What a High Tunnel Actually Looks Like

If you’ve never seen one up close, picture a Quonset hut made of galvanized steel pipe: 14 to 30 feet wide, 10 to 14 feet tall, 48 to 96 feet long. A single layer of 6-mil greenhouse-grade polyethylene stretches over the frame. The sides roll up for ventilation. That’s it.

There are three common configurations:

Single-bay fixed tunnels are the standard. You sink the ground posts, bend the hoops, attach the purlins, pull the plastic, and you’re done. These handle snow loads up to about 25 pounds per square foot if built correctly. Most growers in the Midwest and Northeast run these.

Caterpillar tunnels are the budget option. They use lighter-gauge pipe, sit lower to the ground (usually 6 to 8 feet at the peak), and cost about 60% less than a fixed tunnel. The tradeoff is that you can’t walk a tractor through one, and they’re more vulnerable to wind. Good for greens, bad for trellised tomatoes.

Movable tunnels ride on skids or rails so you can shift them between plots: grow a crop under cover, then slide the tunnel to fresh ground for the next planting. This avoids soil-borne disease buildup, the number one long-term problem in fixed tunnels. Movable tunnels cost 20-30% more because of the rail system, but some organic growers say the disease avoidance alone covers the difference in two seasons.

What It Costs

Let me give you real numbers.

A 30-by-96-foot fixed high tunnel, the most common size for vegetable growers in the US, runs $6,000 to $10,000 for materials plus $2,000 to $3,000 for site prep, ground posts, end-wall lumber, and doors. Hiring someone to build it adds $2,000 to $4,000. Total all-in: $8,000 to $17,000.

A caterpillar tunnel of roughly the same growing area (say 14 by 100 feet) costs $2,000 to $4,000 for materials. These are genuinely DIY-friendly. One person with a helper can put one up in a weekend. No concrete, no heavy equipment.

Plastic needs replacing every 4 to 5 years. A roll of 6-mil greenhouse film for a 30-by-96 tunnel costs about $400 to $600. Call it $100 to $150 per year. The frame, if it’s galvanized steel, will last 15 to 20 years before you need to think about replacing hoops or purlins.

Drip irrigation inside the tunnel is another $300 to $600 depending on how many beds you’re running and whether you need pressure regulation. If your water source is more than 100 feet away or uphill, factor in an extra $200 to $400 for mainline tubing and fittings. A basic drip tape setup with 8-mil tape, a filter, and a pressure regulator covers most small tunnels for under $500.

The ROI Math

Take tomatoes. In open-field production in Zone 6, you might harvest from mid-July through late September, about 10 to 12 weeks. Under a high tunnel, the same plants can produce from late May through mid-October, sometimes into November if you push it. That’s 18 to 22 weeks of harvest. Nearly double the picking window.

A well-managed 30-by-96 tunnel planted to indeterminate tomatoes can produce 3,000 to 4,500 pounds in a season. At $2.50 to $3.50 per pound (farmers’ market or direct-to-restaurant pricing), that’s $7,500 to $15,750 in revenue. The same ground planted to tomatoes in the open field might net $3,000 to $6,000. The tunnel premium is real, and it comes from two things: a longer season and better fruit quality. No rain-split tomatoes, no mud on the leaves, no early blight spreading every time a thunderstorm rolls through.

Greens pay off differently. A tunnel lets you grow spinach, lettuce, and kale through winter in most of the continental US, no supplemental heat. Plant in October, harvest through March. At $5 to $8 per pound for winter greens at market, a 30-by-96 tunnel can bring in $8,000 to $12,000 in the months when your outdoor fields are frozen solid. For CSA farms, the tunnel keeps your share boxes full through the off-season, which is often what keeps members renewing.

The payback period on a $10,000 tunnel running tomatoes and winter greens typically lands between 12 and 18 months. That’s not a projection. It’s what I’ve seen on farms in Pennsylvania, Michigan, and upstate New York.

Getting Water Inside the Tunnel

This is what first-time tunnel builders overlook. You’ve got 1,500 square feet of covered space and no rain reaches it. Every drop comes through your irrigation system.

Drip tape is the standard: one line per row, spaced 12 to 18 inches apart depending on the crop. Use 8-mil or 10-mil tape. The thinner stuff kinks too easily when you’re moving it between plantings. A pressure regulator set at 10 to 12 PSI keeps the tape from blowing out. Add a 120-mesh screen filter at the water source, because even municipal water picks up sediment on its way to the tunnel.

If you’re growing in raised beds inside the tunnel, which you should be for drainage, the drip lines stay put all season. For in-ground rows, you’ll pull and re-lay the tape between crops. Both work. The raised-bed approach costs more up front (lumber, soil mix) but saves labor long-term.

One trick that experienced tunnel growers use: run a second drip line along the base of each side wall. When you roll up the sides for ventilation, the edge rows dry out faster than the center. That second line keeps the whole planting bed even.

What Goes Wrong

Three things kill the economics of a high tunnel faster than anything else.

Soil salinity. Without rain to flush salts out of the root zone, fertilizer residues accumulate. After three or four years, yields drop and nobody knows why. The fix: once a year, pull the plastic back or open both ends during a heavy rain and let nature do the leaching. Or push extra irrigation water through to flush salts below the root zone. Skip this and your tunnel turns into a salt pan.

Poor ventilation. On a sunny day in April, the temperature inside an unventilated tunnel can hit 100°F while it’s 60°F outside. If you’re not there to roll up the sides by 9 AM, you’re cooking your crop. Automated roll-up systems exist. They run about $300 to $600 per side, and they pay for themselves the first time you can’t get to the farm before noon.

Planting the same crop every year. Tomatoes after tomatoes after tomatoes in the same soil is a recipe for Fusarium wilt, root-knot nematodes, and a yield curve that looks like a ski slope. Grafted rootstocks help, but rotating between crop families is better. This is one argument for movable tunnels, by the way, you get to rotate the ground without having to replumb your irrigation every season.

Is It Worth It for You?

If you’re selling direct, farmers’ market, CSA, or restaurant accounts, the answer is almost always yes. The season extension alone covers the cost, and the quality improvement on sensitive crops (tomatoes, peppers, cut flowers, baby greens) is significant.

If you’re selling wholesale to distributors, the math is tighter. Wholesale tomato prices hover around $0.80 to $1.20 per pound, and at those margins, a tunnel takes 3 to 4 years to pay off instead of 1 to 2. Still worth doing, but you need to plan for the longer runway.

For farms under 5 acres, a single 30-by-96 tunnel is the sweet spot. Big enough to matter, small enough to manage with one or two people. Once you’ve run it for a full season and seen what it does to your revenue in April and November, you’ll start thinking about where to put the second one.

High tunnels aren’t complicated. They’re just a frame, a sheet of plastic, and a drip line. But put those three things together in the right configuration, and suddenly your farm has a whole extra season to work with. That’s not technology. That’s leverage.