Are unheated greenhouses worth it?

Greenhouses allow gardeners to extend the growing season by providing protection and warmth for plants. While heated greenhouses can keep the interior warm even through cold winter months, unheated greenhouses rely solely on sunlight to provide warmth. Unheated greenhouses are a more affordable option, but they come with limitations on which plants can thrive and what time of year they can be used. Assessing whether an unheated greenhouse is worth the investment depends on the gardener’s climate, budget, and goals.

What are the pros of unheated greenhouses?

There are several potential benefits to using an unheated greenhouse:

• Lower upfront cost – Unheated greenhouse kits can be purchased for a few hundred dollars. Heated greenhouses require a significant investment in heating systems and insulation.
• Lower operating costs – No need to pay for electricity or gas to run a heating system over the winter.
• Simple setup – Unheated greenhouses are typically lightweight structures that are easy to assemble.
• Extended fall and early spring growing season – An unheated greenhouse can protect plants from light frosts and extend the growing season a few weeks on either end.
• Winter plant storage – Hardy plants like dormant perennials and shrubs can be overwintered in an unheated greenhouse.
• Propagation space – An unheated greenhouse provides a suitable environment for starting seeds and taking cuttings during cool weather.

For gardeners with a limited budget or basic needs, an unheated greenhouse may provide enough benefits to make it a worthwhile purchase. The low cost and simplicity of an unheated structure makes starting a greenhouse less intimidating for beginners as well.

What are the limitations of unheated greenhouses?

The main drawback of unheated greenhouses is their inability to maintain sufficiently warm temperatures throughout the colder months. Some key limitations include:

• Lack of frost protection – Without a heating system, temperatures inside the greenhouse will still dip below freezing on cold nights.
• Shortened growing season – Tender plants cannot survive throughout winter in unheated greenhouses located in most climates.
• Need for seasonal coverage – Plastic coverings may need removal or venting during summer and replacement in fall to prevent overheating.
• Poor conditions for warm-weather crops – Most fruits and vegetables need consistent warmth to thrive and produce.
• Risk of plant loss – If temperatures drop too low, plants can die off during winter.
• Poor climate control – Lack of ventilation or humidity control options can create suboptimal growing environments.

For gardeners wanting to maximize production, grow heat-loving plants, or start their growing season early, an unheated greenhouse may severely limit their options. The right plants and gardening techniques can help make the most of an unheated space, but temperature regulation will continue to be a challenge.

Which plants can thrive in an unheated greenhouse?

Selecting suitable plants is key to successfully using an unheated greenhouse. Some plants that can tolerate cooler temperatures include:

• Cold hardy greens – Kale, spinach, Swiss chard, some lettuces
• Root vegetables – Carrots, turnips, radishes, beets, potatoes
• Cole crops – Cabbage, Brussels sprouts, broccoli, cauliflower
• Herbs – Cilantro, mint, oregano, thyme, parsley
• Early spring flowers – Pansies, snapdragons, stock, sweet peas
• Cool weather annuals – Snapdragons, calendula, Iceland poppies
• Perennials and shrubs – Flowering quince, hellebore, heather, heuchera

The lowest overnight temperatures in the greenhouse will determine which of these plants have the best chance of making it through winter. Choosing hardy, cold-tolerant varieties within these plant types will also help.

Which regions are best suited for unheated greenhouses?

Unheated greenhouses are most practical in warmer climates. The milder the winters, the broader the range of plants that can be grown. Some examples of suitable climates include:

• Southern Coast – Coastal areas of the southeast and southwest rarely dip below freezing.
• West Coast – Much of coastal California, Oregon and Washington experience mild winters.
• Southwest – Areas like Arizona and New Mexico can support unheated greenhouse growing most of the year.
• Southern States – States like Florida, Texas, and Louisiana can use unheated greenhouses for seasonal extension.
• Cool Mediterranean Climates – Coastal regions from Portugal to Italy to California.
• Oceanic Climates – Parts of Western Europe like England and Ireland.

Gardeners in these warmer regions will have the most options for effectively using an unheated greenhouse year-round. Colder parts of the continental United States, inland Europe, and many other temperate locations may be too frigid in winter for unheated greenhouses without backup heating systems.

What factors influence the performance of an unheated greenhouse?

Several variables impact how efficiently an unheated greenhouse retains warmth:

• Materials – Glass or polycarbonate glazing hold more heat than polyethylene film or plastic sheeting.
• Insulation – Extra insulation panels or bubble wrap can provide greater heat retention.
• Size – Larger structures retain more heat, especially with a high peaked roof.
• Ventilation – Vents allow overheating in summer but also increase heat loss in winter.
• Orientation – Greenhouses oriented east to west maximize winter solar gain.
• Nearby structures – Windbreaks, trees or buildings provide shelter and reduce heat loss.
• Supplementary heat sources – Small portable heaters or underground heating cables can raise temperatures during extreme cold.

An efficiently designed unheated greenhouse with quality glazing materials can stay up to 20°F warmer inside than outdoor ambient temperatures during the day. But as soon as the sun sets, the interior temperature will begin dropping towards the outside temperature. Maximizing solar gain is key to successfully maintaining suitable plant growth conditions.

What are the costs of an unheated greenhouse?

Unheated greenhouses are one of the most budget-friendly options for protected growing spaces. Here are some typical costs:

Greenhouse Size	Cost Range
Small hobby greenhouse (3′ x 6′)	$100 – $300
Medium backyard greenhouse (8′ x 12′)	$300 – $700
Large backyard greenhouse (12′ x 16′)	$700 – $1,500
Commercial greenhouse (20′ x 48′)	$2,000 – $5,000

These prices reflect basic unheated greenhouse kits or structures made from aluminum framing and polycarbonate panels or polyethylene film coverings. Using higher end materials, increased insulation, or a customized design can drive costs up significantly.

Ongoing costs are limited to minor maintenance and replacing plastic sheeting or film covers every 3-4 years as they degrade from UV light exposure. For the space provided, unheated greenhouses provide very economical growing environments compared to other greenhouse options.

What alternatives exist to unheated greenhouses?

For those seeking more year-round growing capability, several other greenhouse options exist:

• Passively heated greenhouses – Use solar energy absorption and retention methods for supplemental heat without added heat sources.
• Heated greenhouses – Use electric or gas heating units and increased insulation for full climate control.
• Indoor growing rooms – Convert basements or spare rooms into windowed plant rooms with artificial lighting.
• Cold frames – Miniature unheated greenhouses, typically used temporarily over raised beds.
• Cloches – Bell jars or plastic domes placed over individual plants like mini-greenhouses.
• Tunnel houses – Tall plastic tunnels that protect rows of crops like hoop houses.

The costs, complexity, and capabilities of these structures vary widely. Gardeners unable to effectively use unheated greenhouses have many other options to explore.

Conclusion

Unheated greenhouses provide an accessible way to gain some of the benefits of protected growing spaces on a limited budget. For gardeners willing to select hardy plants and properly manage temperatures, they can lengthen the growing season and expand gardening possibilities. However, inefficient designs or improperly selected plantings in cold climates are likely to result in disappointment.

Carefully assessing the climate conditions, intended uses, and potential drawbacks can clarify whether an investment in an unheated greenhouse will pay off. Those seeking maximal plant growth and productivity will ultimately require the climate control capabilities of heated greenhouse structures. But casual gardeners focused on expanding their gardening options have much to gain from the simplicity and affordability of unheated greenhouses.