The first time I grew tomatoes past November, I was hooked on protected growing. It was not a real greenhouse, just a cold frame made from old windows and a wooden box, but it extended the season by three weeks and saved a crop that would have frozen. That cold frame led to a polytunnel, which led to a polycarbonate greenhouse, and eight years later I have used every type of protected growing structure available to the home gardener.
This guide covers the full range of outdoor greenhouse options, from the simplest cold frame to a permanent glass house. Each type has a place, and the right choice depends on your climate, your budget, what you want to grow, and how permanent you want the structure to be. The comparison is based on building and using each type, not on catalog descriptions, which means the trade-offs discussed here are the ones you actually encounter.
Cold Frames: The Entry Point
A cold frame is the simplest form of protected growing. It is a low box with a transparent lid, placed on the ground or over a planting bed. The lid captures solar energy, warming the air and soil inside. The box walls block wind and trap the warm air. The result is an environment that is 5 to 15 degrees warmer than the outside, enough to extend the growing season by 2 to 4 weeks on each end.
Design and Construction
A cold frame is a weekend project that costs 30 to 100 dollars. The box can be built from pressure-treated lumber, cinder blocks, or straw bales. The lid can be old windows, a sheet of polycarbonate, or even clear plastic stretched over a frame. The standard size is 4 feet by 2 feet (to match standard window dimensions), but any size works as long as the lid can be lifted for access.
The key design detail is the lid angle. The lid should slope toward the south (in the Northern Hemisphere) at an angle of 15 to 30 degrees. The slope captures more sun (particularly in winter, when the sun is low) and allows rain to run off. A flat lid collects water and shades the interior.
The back wall should be taller than the front wall (typically 18 inches at the back, 12 inches at the front for a south-facing frame). This creates the slope and gives headroom for taller plants at the back. The side walls step down from back to front.
Materials
For the box, use rot-resistant wood (cedar, redwood, or pressure-treated pine). Untreated pine rots in 2 to 3 years. Cedar lasts 8 to 10 years. Pressure-treated pine lasts 10 to 15 years but should be lined with plastic if you are growing food (to prevent chemicals from leaching into the soil, though modern pressure-treated lumber is safer than older formulations).
For the lid, polycarbonate panels (4mm twin-wall) are the best choice. They are lightweight, impact-resistant, and insulate better than single-pane glass. A 4-by-2-foot panel costs 20 to 30 dollars. Old windows work but are heavy, breakable, and the old putty may contain lead.
Uses and Limitations
A cold frame is for low-growing plants: lettuce, spinach, radishes, carrots, and for hardening off seedlings started indoors. It is not for tomatoes or peppers in winter, because the height and insulation are insufficient for tall plants or deep cold.
The cold frame extends the season but does not eliminate winter. In zones 6 and warmer, a cold frame allows winter harvesting of hardy greens. In zones 4 and 5, it extends fall harvest into December and allows spring planting 4 weeks earlier. In zones 3 and colder, a cold frame is useful for hardening off and for early spring starts, but it will not support winter growing without supplemental heat.
The main limitation is temperature management. On a sunny winter day, the temperature inside a closed cold frame can exceed 90 degrees, even when it is 30 degrees outside. The frame must be vented (prop the lid open) on sunny days or the plants will cook. An automatic vent opener (a wax-filled cylinder that opens and closes the lid based on temperature) costs 30 to 50 dollars and solves this problem, but it requires a hinged lid.
Polytunnels: The Middle Ground
A polytunnel (also called a hoop house or high tunnel) is a structure made of metal or PVC hoops covered with a single layer of greenhouse polyethylene film. It is larger than a cold frame, tall enough to walk into, and less expensive than a rigid greenhouse. For many gardeners, it is the sweet spot of cost, size, and performance.
Structure and Materials
A polytunnel consists of hoops (arched ribs spaced 4 to 6 feet apart), a frame (the hoops are connected by ridge and purlin pipes for stability), a base (the hoops are anchored to the ground via ground posts or a wooden base rail), and a cover (the polyethylene film is stretched over the frame and secured).
The hoops can be metal (galvanized steel tubing, 1.5 to 2 inches in diameter) or PVC (1.5-inch schedule 40 pipe). Metal is more durable (lasts 20+ years) and more expensive. PVC is cheaper (lasts 10 to 15 years before becoming brittle) but flexes more in wind and snow. For a permanent structure, metal is the right choice. For a trial or a temporary structure, PVC works.
The cover is greenhouse-grade polyethylene film, 6 mil thick, with UV inhibitors. The film lasts 3 to 5 years before needing replacement (the UV inhibitors degrade and the film becomes brittle and tears). A roll of 6-mil greenhouse film (100 feet by 24 feet, enough for a typical home polytunnel) costs 150 to 250 dollars. Do not use construction polyethylene (the clear plastic from the hardware store), because it does not have UV inhibitors and will degrade in one season.
Sizing
Home polytunnels range from 8 by 12 feet (a small starter tunnel) to 20 by 40 feet (a serious growing structure). For a home gardener, a 12 by 20 foot or 16 by 24 foot tunnel is a practical size. It provides 240 to 400 square feet of growing space, enough for a substantial winter garden or for starting hundreds of seedlings.
The height matters. A tunnel that is too short (under 6 feet at the peak) is hard to work in and overheats (the hot air is too close to the plants). A tunnel that is 7 to 8 feet at the peak is comfortable to work in and provides enough air volume for temperature stability. The sidewalls should be vertical or near-vertical for the bottom 2 to 3 feet (this is called a “high tunnel” design) to provide headroom along the edges.
Cost
A kit for a 12 by 20 foot metal-frame polytunnel costs 600 to 1,200 dollars, depending on the gauge of the metal and the quality of the hardware. A PVC-frame tunnel built from scratch costs 200 to 400 dollars in materials. The film cover is an ongoing cost (replaced every 3 to 5 years at 150 to 250 dollars per replacement).
Performance
A polytunnel extends the growing season by 4 to 8 weeks on each end. In zone 6, a polytunnel allows tomato harvest into November and spring planting in February. In zone 8, it allows winter growing of cool-season crops without any supplemental heat.
The temperature inside a polytunnel can be 20 to 30 degrees warmer than outside on a sunny day. Without ventilation, it can exceed 100 degrees on a sunny spring day. Ventilation is critical. Roll-up sides (the film rolls up 2 to 4 feet on each side) are the standard ventilation method. End-wall doors (a door or a vent at each end) provide additional airflow. An exhaust fan (sized to exchange the tunnel’s air volume every minute) is needed for tunnels in hot climates or for summer growing.
The polytunnel does not hold heat overnight as well as a rigid greenhouse (the single layer of film has an R-value of about 0.8, compared to R-2 to R-3 for twin-wall polycarbonate). On a clear, cold night, the temperature inside a polytunnel can drop to within 5 degrees of the outside temperature. For winter growing in cold climates, you need supplemental heat or an inner layer (a row cover or a second layer of film, inflated with a small blower, which adds R-1 to R-2 of insulation).
Polycarbonate Greenhouses
A polycarbonate greenhouse is a rigid structure with an aluminum or wood frame and walls of twin-wall or multi-wall polycarbonate panels. It is more expensive than a polytunnel but more durable, more attractive, and better insulated. For a gardener who wants a permanent, attractive structure, this is the standard choice.
Panel Construction
Polycarbonate greenhouse panels are twin-wall (two layers with ribs between them) or multi-wall (three or more layers). The walls trap air, which provides insulation. A 4mm twin-wall panel has an R-value of about 1.5. A 6mm twin-wall has an R-value of about 1.8. A 16mm triple-wall has an R-value of about 2.5. Compare this to single-pane glass (R-0.9) and you can see why polycarbonate is popular in colder climates.
The panels are lightweight (a 4-by-8-foot sheet of 4mm twin-wall weighs about 10 pounds, compared to 40 pounds for a sheet of glass). They are impact-resistant (they do not break when hit by hail or a stray baseball). They diffuse light (the light passes through the walls and scatters, reaching the plants from all angles, which reduces shadows and promotes even growth).
The downside of polycarbonate is that it yellows over time. The UV coating on the exterior surface degrades over 10 to 15 years, and the panels become cloudy and transmit less light. The panels also expand and contract with temperature (more than glass), which means the framing must allow for movement or the panels will buckle and leak.
Frame Materials
Aluminum is the standard frame material for polycarbonate greenhouses. It is lightweight, does not rust, and requires no maintenance. It is also thin (to minimize shadow), which means it is not as strong as wood or steel. An aluminum frame needs a solid foundation (a concrete footing or a treated-wood base) to resist wind.
Wood frames (cedar or redwood) are more attractive and can be built to any size. They are heavier and more stable than aluminum. The downside is maintenance (wood needs sealing or painting every 3 to 5 years) and the thicker frame members cast more shadow.
Cost and Sizing
A kit for an 8 by 10 foot polycarbonate greenhouse (the most popular home size) costs 1,500 to 3,500 dollars, depending on the panel thickness and the frame quality. A 10 by 12 foot kit costs 2,500 to 5,000 dollars. Installation (if you hire it out) adds 500 to 1,500 dollars.
The foundation is an additional cost. A concrete slab or a concrete footing with a gravel floor costs 300 to 800 dollars for a typical home greenhouse. A treated-wood base (4×4 timbers on a level gravel bed) is cheaper (100 to 200 dollars) but less permanent.
Performance
A polycarbonate greenhouse extends the growing season more than a polytunnel because of the better insulation. In zone 6, a polycarbonate greenhouse with a small heater (5,000 BTU) can maintain 40 degrees inside on a 10-degree night, allowing winter growing of cool-season crops. Without heat, it maintains 10 to 15 degrees above outside, which extends the season by 6 to 10 weeks on each end.
The rigid structure is more comfortable to work in than a polytunnel. The straight walls (most polycarbonate greenhouses have vertical sidewalls) provide full headroom along the edges. The door is a real door, not a flap of plastic. The structure is quiet in wind (no flapping film) and sheds snow (if the roof pitch is sufficient, 25 degrees or more).
Glass Greenhouses: The Long-Term Investment
A glass greenhouse is the traditional, permanent structure. It has a frame (aluminum, wood, or steel) and walls of single or double-pane glass. It is the most expensive option but also the most durable, the most attractive, and the best for light transmission.
Glass Types
Single-pane glass (3mm horticultural glass) is the standard. It transmits 90 percent of light (the highest of any glazing material) and lasts indefinitely (glass does not degrade). It has poor insulation (R-0.9) and it breaks (a hailstone or a thrown rock shatters a pane).
Double-pane glass (two layers of glass with an air gap) has better insulation (R-2 to R-3) but is significantly more expensive. Tempered glass is stronger than horticultural glass (it breaks into small, safe pieces rather than sharp shards) and is required by building codes in some jurisdictions for greenhouses accessible to the public.
The light transmission of glass is its primary advantage. Plants in a glass greenhouse get more light than in any other type, which produces stronger growth, particularly in winter when light is the limiting factor. The clarity of glass also means the greenhouse is bright and pleasant to work in, which matters if you spend time in it.
Frame Materials
Aluminum is the standard frame for glass greenhouses. The frame is precision-engineered (the glass sits in channels with rubber gaskets, similar to a residential window) and requires no maintenance. The thin aluminum members maximize light transmission.
Wood frames (typically cedar or mahogany) are beautiful and can be built to any design. They are the choice for high-end custom greenhouses. The maintenance requirement (sealing or painting every 3 to 5 years) is the trade-off.
Cost and Lifespan
A glass greenhouse is the most expensive option. A kit for an 8 by 10 foot glass greenhouse starts at 3,000 dollars and can reach 8,000 dollars or more for a high-quality model with double-pane glass. A custom-built glass greenhouse (designed and constructed by a contractor) costs 15,000 to 50,000 dollars depending on size and features.
The lifespan is the offsetting factor. A well-built glass greenhouse lasts 25 to 50 years or more. The glass does not need replacement (unless broken). The aluminum frame does not rust. The only ongoing costs are the gaskets (replace every 10 to 15 years) and the ventilation and heating equipment.
Performance
A glass greenhouse performs similarly to a polycarbonate greenhouse in terms of season extension, with the advantage of higher light transmission. The disadvantage is poorer insulation (for single-pane glass), which means higher heating costs in cold climates.
The aesthetic is the other performance factor. A glass greenhouse is a beautiful structure that adds value to a property. A polytunnel is a functional structure that does not. If the greenhouse is visible from the house or the street, and if you care about appearance, glass is the choice.
Comparison Table of All Options
| Feature | Cold Frame | Polytunnel | Polycarbonate | Glass |
|---|---|---|---|---|
| Initial Cost | 30 to 100 dollars | 200 to 1,200 dollars | 1,500 to 5,000 dollars | 3,000 to 8,000+ dollars |
| Lifespan | 5 to 10 years | 10 to 20 years (film: 3 to 5) | 15 to 25 years | 25 to 50+ years |
| Insulation (R-value) | 0.5 to 1.0 | 0.8 | 1.5 to 2.5 | 0.9 (single) to 3.0 (double) |
| Light Transmission | 85 percent | 85 percent | 75 to 80 percent | 90 percent |
| Size Range | 2×4 to 4×8 ft | 8×12 to 20×40 ft | 6×8 to 12×20 ft | 6×8 to 20×40 ft |
| Height | 12 to 18 inches | 6 to 8 feet | 7 to 9 feet | 8 to 10 feet |
| Season Extension | 2 to 4 weeks | 4 to 8 weeks | 6 to 10 weeks | 6 to 10 weeks |
| Wind Resistance | Low | Medium (with anchoring) | High | High |
| Snow Load | Low | Medium (with frame gauge) | High | High |
| Maintenance | Low (replace lid) | Medium (replace film every 3 to 5 yrs) | Low (clean panels) | Low (clean glass, replace gaskets) |
| Aesthetics | Functional | Functional | Attractive | Beautiful |
| Best For | Season extension for low crops | Large-scale season extension | Permanent home greenhouse | Lifetime greenhouse, high light |
Site Selection and Orientation
The location of the greenhouse determines its performance more than any other factor. A greenhouse in the wrong spot, no matter how well-built, underperforms.
Sun Exposure
The greenhouse needs full sun, particularly in winter when light is scarce. In the Northern Hemisphere, the ideal orientation is south-facing (the long axis runs east to west, so the long south wall captures maximum winter sun). The greenhouse should receive sun from 9 AM to 3 PM in winter, with no shade from buildings or evergreen trees.
Deciduous trees on the south side are acceptable (they lose their leaves in winter, allowing sun through), but evergreen trees on the south side block winter sun and should be removed or the greenhouse relocated.
Morning sun is more valuable than afternoon sun, because it warms the greenhouse after the cold night. Afternoon sun is more likely to cause overheating. If you must choose, prioritize morning sun.
Wind Exposure
Wind is a double-edged sword. A windy site provides natural ventilation (which reduces overheating) but increases heat loss (wind strips the warm air from the greenhouse surface) and structural stress. A site with moderate wind protection (a windbreak of trees or a fence, set back far enough to not shade the greenhouse) is ideal.
The prevailing wind direction matters for ventilation. If you rely on natural ventilation (roll-up sides, vents), the vents should be on the prevailing wind side to maximize airflow. If you use an exhaust fan, place the fan on the leeward side (the fan pushes air out, and the intake vents on the windward side let fresh air in).
Drainage
The greenhouse needs well-drained ground. A greenhouse in a low spot collects cold air (frost pockets) and surface water (which floods the interior). Choose a site that is level or slightly elevated relative to the surrounding ground. If the site is not level, grade it before construction.
The interior floor of a greenhouse is typically gravel (for drainage) or concrete (for cleanliness and heat storage). A gravel floor drains well, is cheap, and allows water to pass through (important if you water plants on the floor). A concrete floor is clean and stores heat (it absorbs sun during the day and releases it at night) but requires a drain and prevents water infiltration.
Proximity to Utilities
If you plan to heat, light, or water the greenhouse, proximity to electrical and water service matters. Running electrical to a greenhouse 100 feet from the house costs 500 to 1,500 dollars (trench, wire, conduit, sub-panel). Running water costs 200 to 500 dollars for a buried line. If the greenhouse is close to the house, these costs drop significantly. Plan the location with utilities in mind.
Orientation Detail
For a freestanding greenhouse, the ridge (the peak of the roof) should run east to west. This orientation maximizes the south-facing surface area, which captures the most winter sun. The south-facing wall and roof are the primary solar collectors.
For a lean-to greenhouse (attached to the south wall of a house or other building), the orientation is fixed by the building. The lean-to benefits from the thermal mass of the building wall (which stores heat) and from proximity to the house (easy access, shared utilities). The downside is limited size (the greenhouse cannot be wider than the wall it attaches to) and potential shading from the building in the morning and evening.
Ventilation and Temperature Control
A greenhouse without ventilation is an oven. On a sunny day, the temperature inside a closed greenhouse rises 1 to 2 degrees per minute, reaching 100 to 120 degrees within an hour. Ventilation is not optional, it is the most important system in the greenhouse.
Natural Ventilation
Natural ventilation uses the stack effect (hot air rises) and wind pressure to move air through the greenhouse. The standard setup is roof vents (high, on the roof) and side vents or roll-up sides (low, on the walls). Hot air exits through the roof vents, and cool air enters through the side vents.
For natural ventilation to work, the vent area must be adequate. The rule of thumb is that the total vent area should be 20 to 30 percent of the floor area. A 100-square-foot greenhouse needs 20 to 30 square feet of vent area, split between roof and side vents.
Natural ventilation is free to operate (no electricity) and quiet. The downside is that it depends on wind and temperature differential. On a still, overcast day, natural ventilation does not move much air. And on a hot day with no wind, the greenhouse can still overheat.
Mechanical Ventilation
Mechanical ventilation uses an exhaust fan (typically a shutter-mounted fan in one end wall) and intake louvers (in the opposite end wall). The fan pulls air through the greenhouse, creating positive airflow regardless of wind or temperature.
Size the fan to exchange the greenhouse air volume every minute. For a 100-square-foot greenhouse with an 8-foot peak, the air volume is 800 cubic feet. The fan should be rated for 800 CFM (cubic feet per minute). A typical home greenhouse fan (16-inch, 1/15 HP) costs 100 to 200 dollars and moves 1,000 to 1,500 CFM, which is adequate for most home greenhouses.
Mechanical ventilation requires electricity and it makes noise. The advantage is reliability and control. A thermostat-controlled fan turns on when the greenhouse reaches a set temperature (say, 75 degrees) and turns off when it cools. This automated control is the difference between a greenhouse that bakes its plants and one that maintains a steady temperature.
Heating
For winter growing in cold climates, the greenhouse needs heat. The heating options are electric, gas, and solar (thermal mass).
Electric heaters are the simplest for small greenhouses. A 1,500-watt electric heater (5,100 BTU) maintains 40 degrees in a 100-square-foot greenhouse down to about 20 degrees outside. For colder temperatures or larger greenhouses, you need a bigger heater or a gas heater.
Gas heaters (propane or natural gas) are more powerful and cheaper to operate than electric. A 20,000 BTU gas heater maintains 50 degrees in a 200-square-foot greenhouse down to 0 degrees outside. The heater must be vented (combustion gases include carbon monoxide) and it needs a fuel supply (a propane tank or a natural gas line).
Thermal mass is a passive heating approach. Water barrels (55-gallon drums filled with water, painted black) absorb heat during the day and release it at night. A 55-gallon barrel stores about 450,000 BTU of heat (enough to raise a 100-square-foot greenhouse by about 10 degrees on a winter night). The disadvantage is the space the barrels take up and the limited heating capacity. Thermal mass extends the season but does not replace a heater in cold climates.
Temperature Management Strategy
The goal is to maintain a temperature range suitable for the plants you are growing. Cool-season crops (lettuce, spinach) want 45 to 65 degrees. Warm-season crops (tomatoes, peppers) want 60 to 85 degrees. Most greenhouses are managed for a compromise: 50 degrees minimum in winter, 80 degrees maximum in summer.
The strategy: in winter, heat to 50 degrees (with a heater and thermal mass) and vent at 65 degrees (with a crack of the roof vent). In summer, do not heat (let the temperature follow the outside, with ventilation to prevent overheating). In spring and fall, manage the transition with vents and occasional heat.
Foundation, Anchoring, and Interior Systems
The foundation determines whether the greenhouse stays put in a windstorm and whether the doors and vents operate correctly (a frame that shifts will bind the doors and crack the glass).
Foundation Types
For a cold frame: no foundation needed. The frame sits on the ground or on a layer of gravel.
For a polytunnel: ground posts (metal pipes driven 2 to 3 feet into the ground at each hoop location) are the standard anchoring. The hoops slide over the ground posts. In high-wind areas, a wooden base rail (4×4 treated timber, anchored with rebar stakes every 4 feet) provides additional anchoring and a surface to secure the film.
For a polycarbonate or glass greenhouse: a permanent foundation is required. The options are a concrete slab, a concrete footing (a trench filled with concrete, with a treated-wood sill on top), or a treated-wood base (4×4 timbers on a level gravel bed, secured with ground anchors).
A concrete slab is the most permanent and the most expensive (300 to 800 dollars for a typical home greenhouse). It provides a clean, level floor and excellent anchoring. It requires a drain (a 2-inch pipe through the slab to a dry well or landscape area) to prevent flooding.
A concrete footing with a wood sill is a good compromise. The footing (12 inches deep and 8 inches wide) provides anchoring. The wood sill (treated 4×4) provides a surface to attach the greenhouse frame. The interior is gravel. Cost: 200 to 400 dollars.
A treated-wood base is the cheapest (100 to 200 dollars) and is adequate for small greenhouses in sheltered locations. The base is 4×4 timbers, joined at the corners, set on a level bed of gravel. The timbers are secured with ground anchors (auger-style stakes driven 2 feet into the ground at each corner). This base is not as stable as concrete but it is adequate for most home greenhouses.
Anchoring
Whatever the foundation, the greenhouse frame must be anchored to it. For metal frames, this means bolting the base rails to the foundation (using anchor bolts in concrete, or lag screws in wood). For PVC polytunnels, the hoops are attached to the base rail with pipe straps or brackets.
The anchoring must resist wind uplift (wind blowing over the greenhouse creates a low-pressure area that can lift the structure) and lateral force (wind pushing on the side). A properly anchored greenhouse can withstand 70 to 90 mph winds. An improperly anchored one becomes airborne in a 50 mph gust.
Leveling
The foundation must be level. A frame on an unlevel foundation twists, which binds doors, cracks glass, and prevents vents from sealing. Check the level of the foundation with a 4-foot level (or a water level for longer runs). The tolerance is 1/4 inch over 10 feet. If the foundation is not level, shim the frame (do not force it level by bending the frame, which stresses the joints).
Interior Layout and Systems
The interior layout determines how useful the greenhouse is. A well-organized greenhouse holds more plants, is easier to work in, and performs better than a disorganized one.
Benches and Shelving
Benches (raised tables for plants) are the primary interior structure. The standard bench is 30 inches high (working height), 2 to 3 feet deep (reaching depth), and runs along the walls. The bench surface is slatted (for air circulation and drainage) or mesh (for the same reason). Avoid solid bench tops, which trap water and promote disease.
Bench material: Cedar or redwood slats (attractive, rot-resistant, 8 to 10 year lifespan), wire mesh on a treated-wood frame (cheap, excellent drainage, 5 to 8 year lifespan), or galvanized metal mesh (durable, 15+ year lifespan). Plastic benches (the commercial greenhouse type) are durable and cheap but not attractive.
Shelving (narrower than benches, for smaller plants) can be mounted on the walls above the benches, doubling the growing area. Use adjustable shelf brackets so the shelf height can change with the plants.
Leave a central aisle wide enough to work in (2 to 3 feet for a home greenhouse). A narrow aisle saves space but makes working difficult, particularly when carrying trays.
Water
A water source inside the greenhouse is essential. Running a hose through the door works for a season but is a nuisance. Install a frost-free hydrant (a yard hydrant with a shut-off below the frost line) inside the greenhouse, plumbed from the house water supply. The hydrant provides water year-round (the below-frost shut-off prevents freezing).
A watering wand (a long wand with a breaker nozzle) is the tool for hand-watering. It reaches the back of the benches and provides a gentle flow that does not displace seedlings. For larger greenhouses, consider drip irrigation (tubing with emitters, on a timer), which automates watering and reduces the daily workload.
Electricity
Electricity runs the ventilation fan, the heater, the lights (for seed starting), and any automated controls. Run a dedicated circuit (20 amp, 120 volt) from the house to the greenhouse, buried in conduit at 18 inches deep. Include a GFCI outlet (ground fault circuit interrupter) at the greenhouse, because the environment is wet.
If the greenhouse is far from the house, consider a small solar electric system (a panel, a battery, and an inverter) for low-draw loads like vent openers and small fans. This avoids the cost of trenching a long electrical run, but it cannot power a heater (which draws too much for a small solar system).
Floor
The floor should be weed-free, well-drained, and easy to walk on. The options are gravel, concrete, or pavers.
Gravel (3/4-inch crushed stone over landscape fabric) is the cheapest and drains the best. It is also the most comfortable to stand on (the stone gives slightly). The downside is that weeds eventually grow through (the fabric slows but does not stop them) and dropped tools disappear into the stone.
Concrete is the cleanest and most permanent. It stores heat (a benefit in winter) and can be hosed down. The downside is cost and the need for a drain.
Pavers (concrete or brick, set in sand) are a compromise. They look good, drain reasonably well (through the joints), and are easy to repair (lift and relay). Cost is between gravel and concrete.
The greenhouse I use now is a 10 by 12 foot polycarbonate structure on a concrete footing with a gravel floor. It has an exhaust fan, two roof vents with automatic openers, a 1,500-watt electric heater, and four 55-gallon water barrels for thermal mass. The setup cost about 3,500 dollars (kit plus foundation plus systems) and has been operating for six years with only the fan motor needing replacement. It extends my tomato season by 8 weeks on each end and allows winter growing of greens without supplemental light. That performance, for that cost, is why polycarbonate is the sweet spot for most home gardeners. The cold frame taught me the value of protected growing. The polytunnel taught me the value of size. The polycarbonate greenhouse taught me the value of permanence. Each step up was worth the cost, because the growing season is the most valuable thing a gardener has, and the right structure extends it.
