Hobby Greenhouse Guide: Glazing, Ventilation, Heating and Siting

A small greenhouse extends the growing season, lets you start seeds early, overwinter tender plants and grow crops your climate cannot support outdoors. It also brings challenges a garden shed does not have: overheating on sunny days, heat loss on cold nights, humidity, and glazing that has to survive wind, hail and snow.

This guide explains the choices that matter most when buying or building a hobby greenhouse.

Quick answer

• Size up if you can. Most hobby growers fill a greenhouse quickly, and larger spaces hold temperature more steadily.
• Twin-wall polycarbonate is a practical glazing for most backyard greenhouses: insulating, impact-resistant and light-diffusing. Glass gives the clearest light and longest life but costs more and needs a sturdier frame.
• Ventilation matters more than heating for much of the year. Plan roof vents, automatic openers and shading.
• Site for winter light, away from trees and buildings that cast long shadows.
• Heat safely: use equipment rated for greenhouses, and have any electrical work done by a licensed electrician.

Types of hobby greenhouse

Type	Description	Good for
Cold frame	Low box with a clear lid	Hardening off seedlings, early greens
Mini or walk-in plastic greenhouse	Light frame with plastic cover	Seed starting on a budget; short life and wind risk
Hoop house	Arched frame covered with film	Low-cost growing space, often for vegetables
Lean-to	Built against a wall of the house or garage	Smaller sites; benefits from the wall’s warmth and nearby utilities
Freestanding	Independent structure with gable or arched roof	Most flexible siting and layout

Glazing options

Glazing	Strengths	Trade-offs
Glass (horticultural or toughened)	Clearest light, long life, classic look	Heavier, needs sturdy frame, breakable (toughened glass is safer)
Twin-wall polycarbonate	Good insulation, diffuses light, impact-resistant	Less transparent; quality varies; UV-protected sheets last longer
Single-wall polycarbonate	Light and impact-resistant	Less insulating than twin-wall
Polyethylene film	Lowest cost, good for hoop houses	Needs replacing every few years; check UV rating
Acrylic	Clear and lighter than glass	Can scratch; cost varies

Diffused light from polycarbonate spreads more evenly over plants and reduces scorching. Clear glass gives the most light, which helps in winter but needs shading in summer.

Frames

• Aluminum: light, rot-proof and low maintenance. Thin frames conduct heat out in cold weather.
• Wood: attractive and insulating; choose rot-resistant or treated lumber suitable for a humid environment and plan to maintain it.
• Galvanized steel: strong; common in hoop houses and larger structures.
• PVC and light plastic tubing: inexpensive but weaker in wind and snow.

Check the frame’s stated wind and snow ratings against your local conditions, and anchor the structure as the manufacturer directs.

Siting

• Light: choose the sunniest spot available, especially in winter, when the sun is low. Watch for shadows from trees, fences and buildings.
• Orientation: in northern areas, many growers orient the long side to face south for more winter light. A lean-to on a south-facing wall is a common choice.
• Shelter: a site sheltered from prevailing winds loses less heat and suffers less storm damage, as long as the shelter does not shade it.
• Drainage: avoid low spots where cold air and water collect.
• Access: keep a clear route for wheelbarrows, hoses and power.

Ventilation and shading

On a sunny day, a closed greenhouse can heat up quickly, even in cool weather. Plan for:

• Roof vents, ideally with automatic wax-cylinder openers that open as temperatures rise without power.
• Side or louver vents low down to pull in cooler air.
• Doors that can be left open on hot days, with a screen against pests.
• Exhaust fans with thermostats for larger greenhouses.
• Shading: shade cloth or removable shade paint during summer.
• Air circulation fans to reduce fungal disease in humid conditions.

A min-max thermometer is one of the most useful tools you can buy. It tells you what happened while you were away.

Heating

How much heat you need depends on your climate and what you grow. Keeping a greenhouse just above freezing for overwintering plants needs far less heat than growing warm-season crops in winter.

• Electric heaters with thermostats are clean and easy to control. Use units designed for damp environments, on circuits with ground-fault protection, installed by an electrician.
• Fuel-burning heaters (propane, natural gas, kerosene) can produce carbon monoxide and water vapor. Use only models designed and vented for greenhouses, and follow the manufacturer’s instructions.
• Insulation: horticultural bubble wrap on the inside of glazing reduces heat loss in winter at the cost of some light.
• Thermal mass: water barrels or masonry absorb heat during the day and release it at night, moderating swings.
• Heat mats under seed trays warm the root zone without heating the whole space.

Water and power

• A nearby hose bib or a rainwater barrel saves many trips. Plan drainage for the floor.
• Power for fans, heaters, lights and heat mats should be installed by a licensed electrician to outdoor and damp-location standards.

Foundations and floors

A greenhouse needs a level, stable base and secure anchoring against wind uplift. Common bases include timber frames on compacted gravel, concrete block or paver perimeters, and concrete footings. Gravel floors drain well and add humidity in summer. Paving or concrete is easier to keep clean. Our guide to shed foundation options explains the main base types, most of which also suit greenhouses.

Permits and rules

Small hobby greenhouses are often exempt from building permits, but size limits, setbacks, height rules and homeowners’ association restrictions vary. Larger structures, permanent foundations and electrical or gas connections often need approval. Check with your local building and zoning department first.

Greenhouse or shed?

A greenhouse is a poor place to store tools and equipment because of heat, humidity and sunlight. If you need storage too, a separate shed or a combined shed with a potting area is usually better. See our guide to garden shed materials.

Common mistakes

• Buying the smallest model and outgrowing it in a season.
• Too few vents, leading to overheating.
• Placing the greenhouse where winter shade falls on it.
• Using an unsuitable heater or extension cords in a damp space.
• Inadequate anchoring in windy areas.

FAQ

Is polycarbonate or glass better? Twin-wall polycarbonate insulates better and diffuses light; glass lets in more light and lasts longer. In cold, windy or hail-prone areas, many growers choose polycarbonate.

Can I use a greenhouse without heat in winter? Yes, for hardy greens, overwintering hardy plants and starting seeds early in spring. The greenhouse protects from wind and adds some warmth on sunny days but can still freeze at night.

How do I stop it overheating? Combine roof vents, side vents, an open door with a screen, shade cloth and, if needed, an exhaust fan with a thermostat.