Do mini greenhouses work in winter?

Mini greenhouses, also known as cold frames or cloches, are small enclosed structures used to protect plants from cold weather. They act like small greenhouses, capturing sunlight and trapping heat to create a microclimate that is warmer than the outside temperatures. This allows gardeners to extend the growing season into the cooler months. But do mini greenhouses really work well in winter? Can they provide enough warmth for plants when temperatures drop below freezing?

What are mini greenhouses?

Mini greenhouses, also referred to as cold frames or cloches, are small enclosed structures, usually around 3 to 6 feet wide and 2 to 3 feet high. They are typically made from wood, plastic sheeting, glass or fiberglass and sit directly on top of the soil. The enclosure includes a transparent top that allows sunlight to enter and heat the interior space. The sides help block wind and retain warmth. Mini greenhouses may be permanent structures or temporary season extenders.

Some key features of mini greenhouses:

– Enclosed structure with transparent top
– Traps heat from sunlight
– Creates warmer microclimate inside
– Protects plants from wind, cold, frost and snow
– Portable or permanent
– Come in many sizes, from 2×2 feet up to 4×8 feet
– Allow earlier spring planting and later fall growing
– Can be DIY or purchased

Mini greenhouses go by many names, including cold frames, hot frames, cloches and hoop houses. The terms are sometimes used interchangeably, but there are some differences:

Cold Frames

Cold frames are bottomless boxes with transparent lids that sit directly on the ground. They capture warmth from the sun-heated soil and provide shelter from wind. Cold frames are passive systems with no additional heat source.

Hot Frames

Hot frames are similar to cold frames but include a heating element, historically fermenting manure or compost. This provides extra warmth for heat-loving plants.

Cloches

Cloches are individual plant coverings made of glass or plastic that fit over one or a few plants like a bell jar. They are smaller and more portable versions of mini greenhouses.

Hoop Houses

Hoop houses, also called high tunnels, are larger tunnel-like structures made of hoops or bows covered with plastic sheeting. They are tall enough to walk in and provide shelter for beds of crops.

How do mini greenhouses work?

Mini greenhouses create a warmer microclimate by capturing and storing solar heat energy. During the day, sunlight passes through the transparent glazing material and warms up objects inside. The enclosed space traps this heat and does not allow it to escape easily. At night, a greenhouse holds in heat like the glass roof of a car left sitting in the sun.

Several factors affect the greenhouse heating effect:

– **The greenhouse glazing material** – Glass or plastic sheeting lets in sunlight but reduces heat loss.

– **Ventilation** – Vents release excess heat but allow cold air in. Vents should open during the day only.

– **Insulation** – Added insulation materials hold in more warmth.

– **Thermal mass** – Materials like stone or water inside the greenhouse absorb and slowly release heat.

– **Color** – Dark surfaces absorb more heat from sunlight than light surfaces.

In general, mini greenhouses work by creating a beneficial microclimate around your plants. The enclosed space shields plants from cold winds, frost, snow, and freezing rain. During winter sunlight hours, temperatures inside can be up to 20-40°F warmer than outside. With good heat retention, the greenhouse effect can maintain temperatures above freezing at night. The level of warmth depends on the greenhouse design, materials, and weather conditions.

What are the benefits of mini greenhouses in winter?

Mini greenhouses provide many advantages for winter gardening:

– **Extend the growing season** – Getting a head start on spring planting or growing later into fall.

– **Protect plants from cold damage** – Shield tender crops from frost and freezing temperatures.

– **Create favorable conditions** – Customize a warm, sunny space for heat-loving vegetables and flowers.

– **Grow cool-weather crops** – Grow salad greens, root crops, and hardy greens during winter months.

– **Hardening off seedlings** – Gradually expose tender seedlings to outdoor conditions before transplanting.

– **Overwinter plants** – Store dormant plants like bulbs, tubers, and perennials through the winter.

– **Pest protection** – Keep insect pests and diseases at bay in an enclosed space.

– **Space efficiency** – Make the most of limited garden space by succession planting.

– **Accessibility** – Convenient access to plants for harvesting, watering and tending all season.

– **Weather protection** – Shield plants from heavy rain, snow load, and strong winds.

A mini greenhouse provides insulation and shelter to create ideal conditions for plants during chilly months when gardening is much more difficult. The moderated environment allows plants to photosynthesize and continue growing when they normally would go dormant or die off.

What are the limitations of mini greenhouses in winter?

While mini greenhouses are useful season extending tools, they do have some limitations in the winter:

– **Lack of sufficient warmth** – Most mini greenhouses rely on passive solar heating and do not provide enough heat for warm-weather vegetables on very cold nights. Additional heating may be needed.

– **Overheating** – Greenhouses can get too hot during sunny winter days. Proper ventilation is key.

– **Low light** – Less day length and weaker sun angle in winter means less light for plant growth. Supplemental lighting may help.

– **Cold air intrusion** – Every time the greenhouse is opened, cold outside air rushes in. Minimize opening.

– **Small size** – Limited space for crops, especially large plants or Maximizing space requires careful planning and planting.

– **Condensation and humidity** – Excess moisture can encourage fungal diseases. Good air flow is important.

– **Harsh weather** – Heavy snow or high winds can damage greenhouse coverings. Reinforcement helps.

– **Regular maintenance** – Greenhouses require monitoring and tending year-round to function properly.

– **Rodents and insects** – Hungry critters may try to breach the shelter in search of food.

Even with good design and operation, mini greenhouses have limits in extreme winter weather. Supplemental heat and lighting may be needed to grow more tender vegetables. The tradeoff is higher operation costs and effort.

What plants grow well in winter greenhouses?

Many plants can thrive in a mini greenhouse through winter with proper care. Some top choices include:

Cool-weather vegetables

– Lettuce
– Spinach
– Kale
– Chard
– Carrots
– Beets
– Radishes
– Turnips
– Bok choy
– Broccoli
– Cabbage

These hardy vegetables actually prefer cooler temperatures. They will continue actively growing in winter greenhouse conditions. Many can tolerate light frosts.

Overwintering crops

– Onions
– Garlic
– Leeks
– Potatoes
– Peas
– Fava beans

These crops can be planted in fall and overwintered in the mini greenhouse. Protecting them from harsh weather allows them to resume growth very early in spring.

Summer crops

– Tomatoes
– Peppers
– Cucumbers
– Squash
– Basil
– Melons

Warm-weather loving vegetables can be grown in milder winter areas or with supplemental heat. Opt for quick-maturing and compact varieties suitable for containers.

Herbs

– Parsley
– Cilantro
– Oregano
– Thyme
– Chives
– Rosemary

Many culinary herbs tolerate cold quite well. A greenhouse provides enough protection to keep them actively growing for fresh winter harvest.

Flowers

– Pansies
– Snapdragons
– Calendula
– Cyclamen
– Primrose
– Flowering kale

Hardy annual and perennial flowers thrive in the sheltered environment and provide cheer through dreary winter months. Replace summer favorites with these cold tolerant choices.

The list of potential greenhouse plants is long! Focus on hardy, cold-tolerant choices that can handle some cold nights and short winter days. Be prepared to provide extra protection or heat as needed during severe cold spells.

What are the best materials for winter greenhouses?

Greenhouse construction is important for functionality in cold weather. Look for these ideal features:

– **Glazing material** – Polycarbonate, acrylic or tempered glass panels offer clarity and durability. Double pane improves insulation.

– **Framework** – Use sturdy, reinforced materials like aluminum or powder-coated steel to handle snow load.

– **Insulation** – Add layers like bubble wrap, straw bales, or fiberglass panels for extra warmth.

– **Ventilation** – Roof and side vents with automatic openers prevent overheating.

– **Weather protection** – Choose a sloped roof and wind bracing for snow and rain shedding.

– **Thermal mass** – Incorporate materials like concrete or water containers to absorb and release heat.

– **Wind barriers** – Baffles, interior sidewalls and/or skirt boards reduce cold air intrusion.

– **North wall** – Insulate the north side heavily or bury it into a hill or berm.

With sturdy framing, ample insulation, and smart ventilation, a winter greenhouse will maintain adequate warmth while preventing overheating. High quality materials withstand harsh weather and last for many years.

What is the ideal size for a winter greenhouse?

The right size for your mini greenhouse depends on several factors:

– **Available space** – Measure your yard or garden area for the maximum footprint.

– **Access** – Allow room to move inside for planting, tending and harvesting.

– **Number of plants** – Scale up for larger or multiple beds of crops.

– **Permanent vs. temporary** – Temporary small greenhouses are moved annually.

– **DIY or pre-made** – Pre-made kits come in set dimensions.

– **Solar exposure** – South facing maximizes light for plant growth.

– **Climate** – Colder zones need more space for thermal mass and insulation.

– **Supplemental heat** – Smaller sizes work if you add a heat source.

– **Budget** – Larger greenhouses have higher material costs.

Most home gardeners find a greenhouse in the 4×6 to 4×12 foot range meets their needs. This accommodates 1-3 raised beds with aisle space. Match the size to your gardening goals, space constraints, and budget considerations. Expandable modular designs are popular for starting small and adding on over time.

Where is the best location for winter greenhouses?

Site your greenhouse in these optimal locations:

– **Maximum sun exposure** – Face the long side south for solar heat gain.

– **Near the home** – Makes access convenient for winter use in cold or snowy conditions.

– **Wind protection** – Use buildings, fences and landscaping to block cold winter winds.

– **Good drainage** – Prevent flooding by elevating above wet areas.

– **Level ground** – Especially important for freestanding portable greenhouses.

– **Clearance** – Allow space around the greenhouse for ventilation and maintenance access.

– **Utilities access** – Nearby electrical and water connections make additions like heat and irrigation easier.

– **Security** – Position the greenhouse where you can monitor it and deter vandalism.

Take advantage of natural landscape features like slopes and trees for shelter. Sunny southern exposures are ideal. Make sure the greenhouse is conveniently located for care on cold or stormy days.

How much maintenance is required for winter greenhouses?

While not difficult, mini greenhouses do require regular maintenance and monitoring:

– **Ventilation** – Open vents manually or with automatic openers during warm sunny days to prevent overheating. Close vents at night to retain heat.

– **Watering** – Check soil moisture levels often since enclosed air dries out faster. Water when top inch becomes dry.

– **Critter control** – Check for signs of animal or insect intruders. Make repairs to maintain integrity. Set traps as needed.

– **Temperature monitoring** – Check thermometers inside and out at least twice daily. Make heating or venting adjustments.

– **Cleaning** – Remove debris, clean glazing, and repair weathering when needed.

– **Plant health** – Inspect for pests, diseases, overcrowding etc. and take corrective actions promptly.

– **Structural checks** – Look for sagging, leaks, degraded materials and make fixes before problems escalate.

– **Snow removal** – Clear heavy snow off the greenhouse to prevent collapse.

– **Supplemental heat** – If using a greenhouse heater, check fuel supply and operation.

Daily monitoring and rapid response to issues will keep the greenhouse functioning at its best. Consistent preventative maintenance makes seasonal preparations and repairs easier.

What kind of heating is needed for winter greenhouses?

Many mini greenhouses rely solely on passive solar heating even through winter. But supplemental heat may be desirable for:

– Severely cold climates
– Cloudy periods with limited sunlight
– Warm-weather vegetable crops or seed starting
– Critical overnight freeze protection

Some heating options are:

Electric greenhouse heaters

– Radiant heaters
– Convection heaters
– Under-bench heat mats
– Portable ceramic heaters

Propane greenhouse heaters

– Radiant tube heaters
– Unit heaters
– Portable space heaters

Natural gas heaters

– Unit heaters
– Furnaces
– Boilers with hot water or steam radiators

Key factors in selecting supplemental heat are:

– Greenhouse size and degree of insulation
– Desired minimum temperature
– Electricity and fuel availability
– Budget
– Ease of installation and control

Proper placement, capacity, and control settings are critical to maintain ideal temperatures without over or under-heating.

What are simple DIY winter greenhouse designs?

Here are some basic DIY mini greenhouse designs for winter:

Cloche

A cloche fits over individual plants or rows. Make cloches from:

– Old glass jugs or jars
– Clear plastic bottles with bottoms cut off
– Wire hoops with plastic sheeting cover
– Fiberglass panels
– Straw bales arranged in a tunnel

Cold frame

Build a basic cold frame from:

– Hay or straw bales arranged as walls
– Salvaged windows atop a wooden frame
– Scrap lumber or cinder blocks with plastic sheeting
– Foam board insulation panels for top and sides

Mini hoop house

Use hoops from:

– Bent metal conduit, PVC pipe, or electrical tubing
– Flexible branches, bamboo, or trim scraps
– Cover with poly sheeting, plastic film, old window panes

DIY designs take advantage of inexpensive or free recycled materials. They are simple to construct even for beginners. Start small and expand on the design as desired.

What are the best kits for mini greenhouses?

Purchasing a greenhouse kit offers convenience and quality construction. Some top options are:

Freestanding polycarbonate greenhouses

Prefabricated kits with polycarbonate, plexiglass or fiberglass panels offer light weight and insulation. Many have foldable designs for portability and storage.

Brands: Palram, Outsunny, Best Choice Products, Backyard Greenhouse

Cedar cold frames

Pre-built cedar cold frames are naturally rot resistant and durable. These come disassembled with all hardware included.

Brands: Greenhouse Megastore, Gardener’s Supply, Outsunny

PVC hoop houses

PVC pipe frames with greenhouse sheeting offer affordable prices and easy DIY assembly.

Brands: FarmTek, Gardener’s Supply, Truper hoop benders

Aluminum framed greenhouses

Anodized aluminum provides a corrosion-resistant and sturdy option for permanent installation.

Brands: Juliana, Top Strong New Energy, Lilac House

Choosing quality construction, glazing, and hardware will maximize the lifespan of a greenhouse kit. Consider upgrades like insulation, ventilation, and accessories.

Conclusion

Mini greenhouses are an extremely useful tool for extending the growing season into winter months. They create a protected microclimate through passive solar heating that shelters plants from harsh conditions. Hardy vegetables, leafy greens, root crops and cool weather flowers will continue actively growing in the warmer, humid greenhouse environment.

While mini greenhouses have limitations in extreme cold, their benefits make winter gardening possible and enjoyable. With proper siting, ventilation, and maintenance, backyard greenhouses allow gardeners to stay productive and expand growing possibilities through the winter. When combined with good design, high quality materials, and proper care, mini greenhouses are a worthwhile investment that will keep your garden growing through the off-season.