A $35 cold frame breaks even in under a year. A $2,500 hoop house takes four to five years. A $10,000 polycarbonate greenhouse with a propane heater might never break even if you only use it for hobby seedlings.
The math is not complicated - but you have to actually do it for each structure type, because the numbers are so different that general advice like “season extension pays for itself” is practically useless. This article does the calculation for five structure types, adjusted for what you’re most likely to grow in each.
The Five Structure Types: Cost, Season Gain, and Best Use
Before the break-even math, here is a clear-eyed summary of what each structure type actually does. These cost ranges reflect current retail and direct-from-supplier pricing (2024-2025); actual prices vary by region and supplier.
| Structure | DIY / Installed Cost | Season Extension | Best Use Case |
|---|---|---|---|
| Cold frame | $20-$50 DIY | 4-6 weeks | Hardening off transplants, overwintering greens |
| Low tunnel (row cover + hoops) | $30-$80 per 100 ft | 4-6 weeks | Row crops: lettuce, spinach, carrots, brassicas |
| Caterpillar tunnel | $200-$400 installed | 8-12 weeks | High-value crops needing longer season (tomatoes, peppers) |
| Gothic arch hoop house | $1,500-$4,000 | 12-16 weeks | Tomatoes + peppers (early/late season), year-round greens |
| Polycarbonate greenhouse | $3,000-$15,000+ | Year-round potential | Seed starting, tropical crops, year-round production |
Cold frames and low tunnels are consumable tools with a fast payback. Caterpillar tunnels are a mid-range commitment. Hoop houses and greenhouses are capital investments that require honest accounting of how you’ll actually use them.
Break-Even Calculation 1: Cold Frame
Setup cost: $35 (two salvaged storm windows or one sheet of polycarbonate, a few boards, screws - this is a realistic DIY build).
What it does: Protects a small bed from frost. On a clear night, a well-built cold frame holds 8-10°F above ambient air temperature. In Zone 5, that translates to usable growing conditions from mid-March through late April and again from mid-October through late November - roughly 8-10 additional weeks split across spring and fall.
The calculation:
A standard cold frame covers about 4 square feet of bed space. In spring, that space can run lettuce 4 weeks earlier than your last frost date. Loose-leaf lettuce in 4 square feet, harvested cut-and-come-again style, yields roughly 0.3 lb per week per square foot under good conditions - but realistically, with cold frame density and reduced light, plan on 0.2 lb/week across the bed.
- 4 sq ft × 0.2 lb/week × 4 weeks = 3.2 lb of spring lettuce
At $8/lb for loose-leaf salad mix (USDA AMS specialty crop reports put retail salad mix at $5-$12/lb depending on market), that’s $25.60 from the spring extension alone.
Add a fall extension: the same bed picks up 4 more weeks of spinach or arugula in October-November when outdoor beds have shut down.
- 4 sq ft × 0.2 lb/week × 4 weeks = 3.2 lb × $8/lb = $25.60 fall value
Total annual value from one cold frame: $51.20
Against a $35 build cost, payback arrives partway through your first spring season. If you build it in March and start using it immediately, the cold frame is cash-positive before you finish your taxes.
What changes this math: If you use the cold frame primarily for hardening off transplants rather than production, the savings are real but less direct - you’re protecting the $175-$200 worth of transplants you started indoors, not producing groceries. That still has value, but it’s insurance math rather than production math.
Break-Even Calculation 2: Caterpillar Tunnel
Setup cost: $300 installed. This covers a basic 20-foot caterpillar tunnel - bent EMT conduit or fiberglass rods, greenhouse film, and ground anchors. Pre-made kits from suppliers like Johnny’s Selected Seeds or Farmers Friend run $250-$400 for a 20-30 foot section.
What it does: A caterpillar tunnel over a 20-foot bed adds 8-12 weeks of growing season and provides meaningful frost protection (10-15°F above ambient). More importantly, it raises soil temperature, which matters enormously for heat-loving crops.
The calculation for tomatoes:
A 20-foot caterpillar tunnel over a 4-foot-wide bed gives you about 80 square feet of growing space. Planted with tomatoes at 2-square-foot spacing (indeterminate varieties need more, but 2 sq ft for the footprint plus trellis works in a tunnel), you get roughly 8-10 plants in a single row.
The real payoff is earliness. In Zone 5, outdoor field tomatoes ripen reliably starting in late July. A caterpillar tunnel with transplants set 3-4 weeks early can push first ripe tomatoes to early-to-mid July.
- Early season premium: 4 weeks of July tomato production at 10 lb/week from the tunnel (conservative for 8-10 plants at peak) = 40 lb
- July tomatoes at a farmers market: $3/lb is a fair mid-market price (USDA AMS market data)
- Early season value: 40 lb × $3/lb = $120
Late fall extension adds another increment. The tunnel lets you run tomatoes 4 weeks past your first fall frost date:
- 4 late-season weeks at reduced production (cold slows fruit set): roughly 25 lb total
- Late September tomatoes: $3/lb (market prices hold late in the season)
- Late season value: 25 lb × $3/lb = $75
Total tomato value gain per year: $120 + $75 = $195
Against a $300 investment: payback in 1.5 years.
That’s the optimistic scenario. A more conservative scenario - accounting for years with late blight, poor fruit set, or a tunnel left idle - might average $130-$160/year in real value gain, pushing payback to 2 years. University of Vermont Extension research on high tunnel tomatoes documents season extension gains of 4-8 weeks and yield premiums of 30-50% versus field-grown tomatoes under Vermont conditions - numbers that support the lower end of this range for the Northeast.
One factor that changes everything: You can run cool-season crops in the caterpillar tunnel spring and fall when it would otherwise sit empty. Spinach, lettuce, and arugula in April and October - when no outdoor bed is producing - can add $40-$60/year in value with minimal additional input. That changes the payback to closer to 1.5 years even in the conservative scenario.
Break-Even Calculation 3: Gothic Arch Hoop House
Setup cost: $2,500. This reflects a 12×24 foot structure with galvanized pipe bows, double-layer poly film, and a roll-up side - a common size for a serious home gardener or small market grower. Basic 12×24 kits start around $1,500 and go to $4,000+ with better hardware and additional features (end walls, doors, ventilation).
What it does: A 12×24 hoop house in Zone 5 extends the frost-free growing period from roughly 150 days to 270+ days. That’s not just 6 more weeks - it’s a fundamentally different growing calendar.
The calculation:
The 288 square feet of growing space in a 12×24 house can be divided across three use cases:
Early tomatoes and peppers (96 sq ft, one row each): Set transplants 6 weeks before last frost. In Zone 5, that’s early April instead of mid-May. Tomatoes hit production in late June rather than early August.
- 6 additional weeks of tomato production × 15 lb/week from 6 plants = 90 additional lb
- June tomatoes at farmers market: $4-$5/lb. Use $4 to stay conservative.
- Early tomato value: 90 lb × $4/lb = $360
Late fall peppers add further value. Peppers in a hoop house can run until November in Zone 5:
- 4 additional weeks of pepper production from 8 plants: roughly 40 lb additional
- Late fall peppers: $2.50/lb
- Late fall pepper value: 40 lb × $2.50/lb = $100
Overwintered greens (96 sq ft): Spinach, kale, and arugula seeded in September and protected through winter can be harvested from November through April. This is the most underutilized aspect of an unheated hoop house.
- January salad greens at retail: $8-$12/lb. Use $9 as a midpoint.
- A 96 sq ft greens section with cold-hardy varieties can yield 0.15 lb/sq ft/month in winter (low light, slow growth)
- 96 sq ft × 0.15 lb/sq ft/month × 5 winter months = 72 lb
- Winter greens value: 72 lb × $9/lb = $648
This is the strongest argument for a hoop house that nobody talks about enough. Winter salad greens have the highest retail price of anything you can grow, and an unheated hoop house in Zone 5 can keep them alive and slowly producing when nothing else is.
Annual value summary:
| Use | Annual Value |
|---|---|
| Early tomatoes (6-week extension) | $360 |
| Late fall peppers (4-week extension) | $100 |
| Overwintered greens | $648 |
| Total | $1,108 |
| Against $2,500 investment | Payback in 2.3 years |
That’s a more optimistic figure than the hoop house example in the article brief, and here’s why: the brief’s $550/year estimate omits winter greens production entirely, treating the house as a spring/fall tool only. An unheated hoop house that sits empty from December through March is leaving most of its value on the ground.
More realistic adjusted scenario, accounting for partial-use years and crop failures: $550-$750/year, which puts payback at 3.3-4.5 years. Still a solid return on a durable structure with a 15-20 year lifespan.
University of Vermont Extension’s high tunnel economics research (Parsons, Mayout, 2010-updated) documents that hoop house tomatoes in the Northeast typically return $2-$3 per dollar of structure cost over a 10-year horizon - consistent with these calculations.
The Heating Penalty: Why Heated Structures Change the Math
Everything above assumes an unheated or passively heated structure. Once you add propane or electric heat, the economics change fast.
Consider a 12×24 hoop house in Zone 5 with a propane heater maintaining a 40°F setpoint through winter. This is the minimum temperature to keep most cool-season crops alive and productive.
Propane heating cost estimate:
On a cold December night in Zone 5 (outside temp: 10°F, inside target: 40°F, delta: 30°F), a 12×24 structure with single-layer poly loses heat fast. A 30,000 BTU heater running at 50% duty cycle burns roughly 1-1.5 gallons of propane per night.
- Propane cost (2024-2025): $3.25-$3.75/gallon. Use $3.50.
- 1.5 gallons/night × $3.50/gallon = $5.25/night
- 120 cold nights (November through February in Zone 5): $5.25 × 120 = $630/season in propane
That $630 heating cost lands on top of your $2,500 structure investment. Now your first-year costs are $3,130, and every subsequent winter adds $630 before you grow a single leaf.
The break-even math for a heated greenhouse only works if you’re producing high-value crops year-round at close to capacity. For a home gardener using a heated structure primarily for seedling starts and the occasional winter tomato plant, the propane bill will exceed the harvest value indefinitely.
Where heated structures do pay off:
Seedling production is the strongest case. If you’re starting 50 tomato transplants and 50 pepper transplants that you would otherwise purchase, the math is:
- 100 transplants × $3.50 retail price = $175 in saved transplant costs per year
- Add herb seedlings, annual flower starts, and vegetable succession plantings: realistically $250-$350/year in transplant savings
- A 6×8 polycarbonate cold-attached greenhouse (not the full 12×24) running from February through May might use $80-$120 in propane total. At $3.50/lb for transplants, the numbers work.
The mistake is heating a large structure modestly. A 12×24 hoop house heated for seedling production uses 5x the propane of a small attached greenhouse that would handle the same task. Size the heated structure to the actual job.
Zone-Specific Value: Why Zone 4-5 Gets More from Season Extension
The same structure installed in two different climates does not produce the same value. This is a fundamental point that most season extension guides skip over.
The frost-free season comparison:
| Zone | Avg. Last Frost | Avg. First Fall Frost | Frost-Free Days |
|---|---|---|---|
| Zone 4 (Minneapolis area) | ~May 15 | ~Sept 25 | ~133 days |
| Zone 5 (Chicago area) | ~May 1 | ~Oct 7 | ~159 days |
| Zone 6 (Kansas City area) | ~April 15 | ~Oct 22 | ~190 days |
| Zone 7 (Atlanta area) | ~March 20 | ~Nov 15 | ~240 days |
| Zone 8 (Dallas area) | ~March 1 | ~Nov 28 | ~272 days |
A 12×24 hoop house adds roughly 12-16 frost-free weeks on top of the ambient growing season. In Zone 5, those 12 extra weeks increase the usable season from 159 days to about 243 days - a 53% increase. In Zone 7, the same structure adds 12 weeks to an already-long 240-day season, increasing it to roughly 324 days - a 35% increase.
But the value of those extra weeks isn’t equal either. Early tomatoes in Zone 5 sell for a premium at markets in June because they’re genuinely scarce. In Zone 7, tomatoes are available from field production by mid-May even without a structure. The marginal value of two extra weeks in Zone 7 is lower than the marginal value of six extra weeks in Zone 5.
Calculated zone comparison for a hoop house:
| Zone 5 Gardener | Zone 7 Gardener | |
|---|---|---|
| Weeks of season gained | ~12-14 weeks | ~4-6 weeks |
| Early tomato premium weeks | 6 weeks | 2 weeks |
| Winter greens production window | 5 months | 2 months |
| Estimated annual structure value | $750-$1,100 | $300-$500 |
| Break-even on $2,500 investment | 2.3-3.3 years | 5-8 years |
The same $2,500 investment has roughly 2-3x the payback speed in Zone 5 versus Zone 7. If you’re in Zone 7 or warmer and considering a full hoop house, the honest answer is that a caterpillar tunnel or low tunnel probably serves your needs at a fraction of the cost. Your ambient season is already long enough that major capital structures are hard to justify unless you’re doing high-volume market production.
What Justifies the Cost Beyond the Pure Math
Early Tomatoes at Market Price
The price gap between early-season and late-season tomatoes is real and substantial. At most regional farmers markets in the Northeast and Midwest, the first tomatoes of the season - typically from hoop house growers - sell for $5-$6/lb in June and July. By August, when field tomatoes flood the market, prices drop to $2.50-$3/lb. September sees another bump as field production ends.
If you’re selling at market or pricing against market alternatives, a hoop house that puts you in the $5/lb window for 6-8 weeks versus the $2.50/lb window has meaningful revenue implications beyond simple season extension.
For home gardeners pricing against grocery retail: June grocery store tomatoes are typically $4-$6/lb for any decent quality. August grocery tomatoes are $1.50-$2.50/lb. The substitution value of growing your own June tomatoes is genuinely higher than growing your own August tomatoes.
Seedling Production
Starting your own transplants versus buying them shifts the math on several crops. Typical retail prices for vegetable transplants at independent garden centers (2024-2025): $3.50-$5 per tomato, $2.50-$4 per pepper, $2-$3 per brassica.
If you grow 50 tomato starts, 30 pepper starts, and 20 brassica starts:
- Retail alternative: (50 × $4) + (30 × $3.50) + (20 × $2.50) = $200 + $105 + $50 = $355
- Seed cost: roughly $20-$30 in seeds
- Saved: $325-$335/year from transplant production alone
A cold frame or small unheated greenhouse handles most of this if you’re in Zone 5-6. You don’t need a heated structure to harden off seedlings - you need something that protects them from hard frosts and provides some buffer against late cold snaps.
January Salad Greens
This is the value proposition that people underestimate most. January salad greens at retail cost $8-$12/lb for anything worth eating - organic spring mix, arugula, or specialty lettuce blends. An unheated hoop house in Zone 5 can produce these crops at slow winter growth rates from October-seeded transplants.
Mâche (corn salad), spinach, and cold-hardy arugula varieties can survive temperatures in the mid-teens Fahrenheit with hoop house protection in Zone 5. They grow slowly in December and January - maybe 0.1-0.2 lb per square foot per month - but they grow. That slow winter production, priced against $10/lb retail salad mix, generates significant value from growing space that would otherwise sit empty.
Which Structure Fits Which Situation
One cold frame is the correct first investment for almost every gardener in Zone 4-6. The payback is under a year, the skill it teaches (managing temperature swings, ventilation, plant hardening) applies to every larger structure you might build later, and the build requires no special skills or tools. Build it from salvaged windows if you can find them.
A caterpillar tunnel makes sense once you’re committed to growing tomatoes or peppers at scale and want more consistent production. The 1.5-2 year payback is solid for a structure that lasts 8-12 years with film replacement.
A hoop house is a significant decision that rewards growers who will actually use the winter production capacity. If your plan is “early tomatoes and early peppers and then nothing from November through March,” you’re leaving the most valuable use case untouched and the economics get harder to justify below Zone 5. Do the zone comparison above honestly before committing $2,500+.
A polycarbonate greenhouse with heat is a lifestyle decision as much as a financial one. Run the actual propane numbers for your zone before you buy. The break-even on a heated structure that sees primarily hobby use may extend past 15 years.
For a detailed look at the tools within these structures - row covers, floating cover grades, drip irrigation - see season extension tools and what each actually returns. For crop selection that maximizes the value of your extended season, the best crops by zone breakdown covers which crops gain the most from early planting.
The Break-Even Summary Table
| Structure | Cost | Annual Value Gain | Payback |
|---|---|---|---|
| Cold frame (DIY, 4 sq ft) | $35 | $50-$65 | Under 1 year |
| Low tunnel (per 100 ft row) | $55 avg. | $60-$90 | 1 year |
| Caterpillar tunnel (20 ft) | $300 | $130-$195 | 1.5-2.3 years |
| Gothic arch hoop house (12×24, unheated) | $2,500 | $550-$1,100 | 2.3-4.5 years |
| Polycarbonate greenhouse (12×24, unheated) | $6,000 avg. | $500-$900 | 6.7-12 years |
| Polycarbonate greenhouse (12×24, heated) | $6,000 + $630/yr heating | $700-$1,100 net of heat | May not break even |
All values calculated for Zone 5 unheated use cases. Zone 4 values are 10-20% higher; Zone 6-7 values are 20-40% lower. Structure costs exclude installation labor where applicable.
The cold frame and low tunnel math is nearly identical across all zones because both structures are cheap enough that even modest production value covers the cost quickly. The gap opens at caterpillar tunnel and above, where the longer payback period makes the zone-specific value gap materially significant.
If you’re tracking your actual harvest value to measure this in practice, the Garden ROI app logs harvests by crop and calculates running season totals - useful for building a real dataset over 2-3 seasons to compare against these projections rather than taking any table, including this one, on faith.
High tunnel economics data: University of Vermont Extension, High Tunnel Production Manual, Parsons and Mayout (updated edition). USDA AMS specialty crop market reports used for retail price estimates throughout.