Can you grow anything year round in an unheated greenhouse?

Yes, but only cold-hardy crops, and growth nearly stops from late November to late January in most of the country. An unheated structure typically holds the interior about one USDA zone warmer than outside, so a zone 6 garden behaves like zone 7 inside. Spinach, mache, arugula, kale, claytonia and hardy Asian greens survive that comfortably and can be harvested through winter. What they will not do is grow much: below about ten hours of daylight, plants hold rather than bulk up.

Do greenhouse tomatoes need pollinating by hand?

Usually yes, because the wind and bees that do the job outdoors are absent. Tomatoes are self-fertile but need vibration to shake pollen loose from the anthers. Tapping the flower cluster or the support string once a day around midday, when humidity is lowest and pollen sheds most readily, is enough. An electric toothbrush held against the stem behind the truss works well. Peppers and eggplant benefit from the same treatment; cucumbers grown from parthenocarpic varieties need none.

What is the biggest mistake beginners make in a greenhouse?

Underestimating heat, not cold. A sealed structure in full sun can climb 30 to 40°F above outside air in the middle of a clear spring day, which cooks seedlings in an afternoon in March, long before anyone is thinking about summer. The fix is ventilation opening automatically rather than when you remember: a solar-powered vent opener costs little, needs no electricity, and opens on temperature. Shade cloth handles the peak of summer.

Should beginners start plants from seed or buy transplants?

Start seeds. Raising your own transplants is the single most valuable thing a small greenhouse does, because it gives you six to eight weeks on the season, access to hundreds of varieties no garden center stocks, and a cost per plant measured in cents. Seed starting also happens in late winter and early spring, exactly when the greenhouse is otherwise idle, and the trays come out before the summer crops need the bench space.

How much can one small greenhouse actually produce?

A 6-by-8 foot greenhouse with good management supports roughly four to six staked tomatoes or a mix of two tomatoes, two peppers, one cucumber and a bench of greens, plus several hundred spring transplants raised before the summer crop goes in. That is a meaningful supplement rather than self-sufficiency. Owners consistently report that the seed-starting and season-extension value outweighs the summer crop value in a structure that size.

What to Grow in a Greenhouse for Beginners

Written & researched by Elena Marsh Gardening & Landscaping Editor

Updated October 2026

Low-angle view of a person opening the vent of a backyard greenhouse full of seedlings, in soft overcast light

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Start with five: leafy greens, herbs, tomatoes, peppers and cucumbers. Greens and herbs are the genuine beginner crops because they tolerate the wide temperature swings a first greenhouse inevitably produces, they crop within weeks, and a failure costs you very little. Tomatoes, peppers and cucumbers are the three that repay greenhouse space most in flavor and yield, and all three want the same conditions, so they can share a structure without conflict. Add a spring seed-starting bench and a small greenhouse earns its cost before summer.

Which crops are hardest to kill?

Crop	Sow	To harvest	Why it suits beginners
Lettuce & salad mix	Feb–Sep	25–45 days	Fast, forgiving, cut and come again
Spinach & arugula	Sep–Mar	30–45 days	Thrives in cool; winter workhorse
Radish	Feb–Apr	25–30 days	Fastest visible result in the house
Basil & soft herbs	Mar–Jul	40–60 days	Loves warmth and shelter
Tomatoes	Feb–Mar start	65–85 days from set	Biggest quality gain over outdoors
Peppers & chiles	Feb start	70–90 days	Ripens fully in short-season states
Cucumbers	Apr–May	50–70 days	Heavy yield from one vine

Radishes are worth sowing in the first week purely as feedback. They germinate in three days and are edible in a month, which tells you the house is working before anything slower has committed.

Close-up detail of the material being worked in a greenhouses & season extension project, in soft overcast light

What grows in each season?

A small greenhouse has four distinct phases, and planning around them is what separates a productive house from one that sits empty half the year.

Late winter, February to March. Seed starting on a heated mat, plus hardy greens already in the ground from fall. This is the highest-value period in the whole calendar.

Spring, April to May. Transplants hardening off, early salad, radish, and the first tomatoes and peppers going into their permanent positions once night temperatures inside stay reliably above 50°F.

Summer, June to September. Tomatoes, peppers, cucumbers, basil, eggplant. Ventilation and shade become the whole job — heat, not cold, is the summer constraint.

Fall and winter, October to January. Clear the summer crop, sow spinach, mache, claytonia, kale and hardy Asian greens by early October so they reach useful size before day length drops. Growth stalls midwinter and resumes in February. The crops that hold through are listed in unheated greenhouse winter crops.

Three-quarter view of a person opening the vent of a backyard greenhouse full of seedlings, in soft overcast light

What should a beginner not try first?

Melons and winter squash, because they sprawl over an area a small house cannot spare and demand hand pollination of separate male and female flowers. Corn, which is wind-pollinated and needs a block to set properly. Full-size fruit trees, which outgrow the structure. And anything that requires a reliably heated house through winter, such as tropical fruit — heating a hobby greenhouse to 60°F through a northern winter costs more than the produce is worth, as the numbers in how to heat a greenhouse in winter make clear.

Wide view of a person opening the vent of a backyard greenhouse full of seedlings, in soft overcast light

What does the house itself need?

Three things before any seed goes in: automatic ventilation, because unattended overheating kills more greenhouse plants than cold does; a thermometer that records the daily minimum and maximum, so you know what your structure actually does rather than what you assume; and a watering plan, since nothing inside receives rain. Siting and sizing decisions are covered in greenhouse sizing and siting, and the overheating problem specifically in greenhouse ventilation and overheating.

If you have not bought a structure yet, our best backyard greenhouse roundup ranks on the durability and wind resistance owners report over multiple seasons. For a smaller start, a cold frame does much of this work for a fraction of the cost — see how does a cold frame work.

We never buy, test or physically handle the products we rank. Recommendations come from aggregated owner reviews, star ratings, review volume and expert consensus — see how we rank.