Food · Growing
Not free food year-round. A greenhouse buys a household six to eight weeks of growing season at each end, and protects cold-hardy greens through a mild winter, if the ventilation and heat are managed correctly.
What this buys you
A greenhouse traps solar heat and blocks wind and frost, which lets a household start seeds earlier, keep tender crops going later, and grow cold-hardy greens through a mild winter. It does not replace daylight — a greenhouse in a northern climate still faces shorter, weaker winter light, which limits what grows well without supplemental lighting.[1]
Full glass or polycarbonate greenhouses with heating and cooling are the most capable option and the most expensive to run. Unheated hoophouses and high tunnels cost far less, extend the season by roughly six to eight weeks on each end, and are the more realistic starting point for most households.[1]
Before building or buying anything, decide honestly which of these two jobs the structure is for: stretching the season on crops you already grow, or running heated, year-round production. The second is a real commitment in fuel or electricity cost, not a weekend project.
Getting started
A low box with a clear lid set directly over a garden bed. Cheapest and simplest option, good for hardening off seedlings and protecting a single bed of greens through frost.
Hoops and fabric or plastic over a row of crops. Most row covers protect down to about 24 to 28°F. Cheap, portable, no ventilation system needed for fabric versions.[1]
Tall enough to stand in, a metal or plastic-rib frame with greenhouse plastic stretched over it. No active heating or cooling, but roll-up sides give real ventilation control. The realistic middle ground for a serious backyard grower.[1]
Glass or rigid polycarbonate with active heating, cooling, and often supplemental light. Lean-to models attach to an existing building; freestanding models need east or south exposure and at least 5 to 6 hours of unobstructed winter light.[2]
The work
Below 50°F
Most vegetable crops stop growing entirely. Cold-hardy fall greens tolerate down to about 45°F.[3]
68–78°F
The target range for most vegetable and flower crops. Plants grow faster and flower earlier here than at any other range.[3]
90°F+
A sealed greenhouse can run 40 to 50°F above outside air — a mild 65°F afternoon can push the interior past 110°F within an hour without ventilation.[4]
The most-skipped step
Overheating from inadequate ventilation, not cold, is the most common way new greenhouse owners lose plants. The instinct to seal a greenhouse tight against winter cold backfires — it traps humidity instead, and that humidity feeds fungal disease.[4]
Roof vents, roll-up sides, and doors let hot air rise and escape while cooler air enters low. No electricity required, and it works especially well in a breeze — a wind speed of just 2 to 3 mph can provide most of the air exchange in a well-designed structure.[5]
Sizing rule: combined vent area should equal roughly 15 to 20% of the floor area.[5]
An exhaust fan paired with intake vents on the opposite wall drives air exchange on still, hot days when passive vents alone can't keep up. A thermostat-controlled fan handles the job automatically rather than requiring someone to babysit vents all afternoon.
Sizing rule: fan capacity should change the full air volume of the greenhouse about once a minute.[2]
Small hobby greenhouses are often heated with low-cost space heaters, or gas, oil, or coal-fired units for larger structures. Any fuel-burning heater requires a fresh air supply and proper exhaust venting to prevent carbon monoxide and ethylene buildup inside the structure.[2] A sealed, unventilated greenhouse with a fuel heater running is a carbon monoxide risk, not just a plant-health one.
Electric heat (forced-air with a thermostat, or overhead infrared paired with soil cable heat) avoids the combustion risk entirely and is the simpler choice for a small hobby structure. Whatever the heat source, a temperature alarm that flags power failures or extreme swings is worth the cost for anything beyond a cold frame.[2] See the Energy section for full carbon monoxide safety guidance.
Where it leads
A longer season means an earlier and later harvest — the same preservation and storage skills that handle a summer glut apply to a greenhouse's extended one.
Site selection and soil basics that apply just as much inside a greenhouse bed as outside one.
Read the guide →
Pest management and season planning carry over directly to a greenhouse's longer, more controlled growing window.
Read the guide →
An earlier spring harvest and a later fall one both need somewhere to go. Compare canning, drying, and fermenting.
Read the guide →