Greenhouses, Polytunnels and Cold Frames – Which to Choose for Your Garden

Greenhouses, Polytunnels and Cold Frames – Which One to Choose for Your Garden

Greenhouses, polytunnels and cold frames – which one to choose for your garden

Extend the growing season, protect heat-loving plants from spring frosts, grow tomatoes without mildew – a covered growing space makes all this possible. But which type should you choose? Greenhouses, polytunnels and cold frames differ in price, durability and what you can grow in them. This guide will help you select the right structure, materials and equipment, and show you how to get the most out of them throughout the year.

Why Grow Under Cover?

A covered growing space offers benefits that an outdoor bed can never provide:

• Extended season – start growing 4–8 weeks earlier and extend harvest by 4–6 weeks in autumn
• Protection from bad weather – rain, hail, wind and late spring frosts are no longer a problem
• Environment control – you have full control over temperature, humidity and watering
• Fewer diseases – potato blight on tomatoes spreads through wet leaves; under a roof they stay dry
• Higher and more stable yields – consistent conditions lead to better quality and quantity of fruit
• Exotic crops – peppers, aubergines, melons, cucumbers or basil ripen safely even in Czech climate

Types of Covered Growing Spaces

Greenhouses

A greenhouse is a permanent structure with a solid frame made of aluminium, steel or wood and a transparent covering of glass or polycarbonate. It is the most expensive option, but also the most durable and efficient for year-round growing.

Advantages:
- Excellent thermal insulation, especially with double-wall polycarbonate
- High resistance to wind and snow load
- Possibility of year-round operation with heating
- Lifespan of 20–30 years or more
- Aesthetic value for your garden

Disadvantages:
- Higher purchase price
- Requires a quality foundation – concrete pads or perimeter frame
- Legal conditions – greenhouses up to 40 m² of footprint and 5 m height are classified as minor structures (no permit required, but you must meet legal conditions)

In the selection of greenhouses on Pestik.cz you will find models from compact balcony structures to spacious garden greenhouses for demanding growers.

Polytunnels

A polytunnel consists of steel or aluminium arches covered with polyethylene (PE) or PVC film. It offers excellent value for money, especially for larger growing areas.

Advantages:
- Significantly lower purchase price than a greenhouse
- Quick and easy assembly
- Large interior volume for reasonable money
- Relatively easy to relocate
- Good light transmission

Disadvantages:
- Shorter film lifespan – 3–5 years for standard PE, 7–10 years for UV stabilised variants
- Poorer thermal insulation and greater temperature fluctuations compared to a greenhouse
- Lower wind resistance and snow load capacity
- Less representative appearance

In the polytunnel category on Pestik.cz you will find models in various arch lengths and diameters.

Cold Frames

A cold frame is a low structure 30–60 cm tall with a transparent lid, designed primarily for raising seedlings and gradually hardening them off. It can be portable or permanently built into a bed.

Advantages:
- Very low price
- No building requirements
- Creates effective microclimate for germination and early growth
- Ideal for hardening off seedlings before moving to the bed
- Extends season for lettuce, radishes and corn salad

Disadvantages:
- Limited space and height prevent growing tall plants
- Cannot be used for tomatoes, cucumbers or other climbing plants
- Manual ventilation requires daily attention – on sunny days you must open the lid

Portable and foldable cold frames are a practical addition to any garden and a great starting point for beginner growers.

Comparison of Covering Materials

Feature	Tempered Glass	Double-wall Polycarbonate	UV Stabil. PE Film	PVC Film
Light transmission	90–92%	80–85%	85–90%	80–85%
Insulation (U-value)	5.8 W/m²K	3.0–3.6 W/m²K	6.0+ W/m²K	5.5+ W/m²K
Lifespan	30+ years	15–20 years	3–5 years	5–7 years
Hail resistance	Low (shatters)	High (200× stronger than glass)	Medium (punctures)	Medium
Weight	High	Low	Very low	Low
Price per m²	300–600 CZK	200–400 CZK	30–80 CZK	50–120 CZK
Maintenance	Cleaning	Cleaning, monitor UV degradation	Replacement after 3–5 years	Replacement after 5–7 years

Glass – Classic for Demanding Growers

Tempered safety glass offers the best light transmission and virtually unlimited lifespan. Unlike plastics, it does not cloud from UV radiation or condensate on internal surfaces. However, expect higher weight requiring a more robust frame and risk of breakage from impact.

Polycarbonate – Best Value for Money

Double-wall (cellular) polycarbonate is now the most common material for garden greenhouses. The air gap between the walls provides significantly better thermal insulation than plain glass – heating energy consumption can be up to 50% lower. The material is lightweight, resistant to hail and easy to cut and install. The disadvantage is gradual yellowing and loss of transparency from UV radiation – quality sheets with UV protective coating significantly slow this process.

PE Film – Economical Option for Polytunnels

Polyethylene film with UV stabiliser is the standard for polytunnels. It is the cheapest, lightest and in basic versions lasts 3–5 years. Modern reinforced or multi-layer PE films achieve a lifespan of 7–10 years and better withstand wind damage.

Choosing the Right Size

Recommended Minimum Dimensions

Purpose	Minimum Area	Recommended Area	Ridge Height
Seedling raising	2–4 m²	4–6 m²	1.5 m
Tomatoes + peppers (2 people)	6–8 m²	10–12 m²	2.0 m
Year-round growing (family)	12–15 m²	18–25 m²	2.2–2.5 m
Semi-professional operation	25+ m²	40–60 m²	2.5–3.0 m

Rule of thumb: Larger rather than smaller. The vast majority of growers regret after the first season that they didn't choose a more spacious structure. Extra space also allows better air circulation, which naturally reduces the risk of fungal disease.

Width: Minimum 2.5 m for two beds and a walkway. For comfortable work with a wheelbarrow or carriers we recommend a width of 3–4 m.

Location: Orient the longer axis east–west to maximise sun exposure throughout the day. Avoid shade from buildings, fences and trees. Access to water and electricity will greatly simplify growing.

Foundation and Anchoring

Types of Foundations

• Concrete pads – the most stable solution for permanent greenhouses. A concrete point under each frame post ensures wind resistance and protection against frost heave.
• Concrete strip – perimeter foundation approximately 30 × 30 cm is ideal for larger greenhouses and allows better sealing of the bottom edge.
• Steel foundation frame – anchored to the ground with ground screws. Quick assembly without concreting, sufficient stability for small and medium structures.
• No foundation – acceptable only for smaller polytunnels anchored with steel pegs. Less stable and more prone to movement in strong wind.

Building Regulations

According to the new Building Act (effective from 1 July 2024), greenhouses fall into the category of minor structures if they meet these conditions:
- Footprint up to 40 m²
- Height up to 5 m
- No basement
- Minimum 2 m distance from neighbouring property boundary

Minor structures do not require a building permit or approval. However, you must comply with the above limits, territorial plan compliance and any rules for the area (protected areas, national parks etc.).

Ventilation – Key to Successful Growing

Overheating is a much more common problem in Czech climate than undercooling. On a summer sunny day, temperature in a closed greenhouse without ventilation can exceed 50 °C – a level at which tomato pollen dies, leaves wilt and fungi spread rapidly. Proper ventilation is therefore an investment that directly translates to yield.

Types of Ventilation

Type	Principle	Advantages	Disadvantages
Roof vents	Manual or automatic	Hot air naturally rises and escapes	Manual opening/closing required
Side vents	Manual or automatic	Cross-flow, cooler air intake	Less effective than roof vents
Doors	Manual	Simple, no cost	Insufficient for larger areas
Automatic openers	Wax piston (temperature triggered)	Maintenance-free, no electricity required	Slower response to temperature changes
Forced ventilation	Electric fan with thermostat	Precise and rapid control	Requires power supply

Rule: Ventilation area should be at least 20% of greenhouse floor area. For a 10 m² greenhouse this means at least 2 m² of openable surfaces combining roof vents and doors.

Automatic openers based on wax piston principle (e.g. Univent) are a cost-effective and reliable choice. When the set temperature is reached, usually 20–25 °C, the wax piston expands and automatically opens the vent – without electricity or supervision.

Heating

For year-round use or reliable protection against spring and autumn frosts, heating is essential. Properly sized heating can easily extend the season by 3–4 months.

Heating Type	Investment	Operating Costs	Output	Suitable for
Electric immersion heater	Low	High	1–3 kW	Small greenhouses, backup heating
Infrared heater	Medium	Medium	0.5–2 kW	Targeted local heating
Paraffin heater	Low	Medium	1–2 kW	Greenhouses without electricity
Underfloor heating	High	Low (heat pump)	Variable	Large greenhouses with permanent operation
Compost heat	None	None	Moderate	Cold frames and raised beds

Tip: A thermostat is essential – unnecessarily overheated greenhouse increases running costs and weakens plants. Maintain minimum night temperature of 5–7 °C for frost-hardy crops (lettuce, spinach, corn salad) or 12–15 °C for heat-loving varieties (tomatoes, peppers, cucumbers). Double film or bubble insulation placed on the inside of walls will reduce heat loss by 30–40% and quickly pay for itself through reduced heating investment.

Shading

In summer, excessive sunlight can be as damaging as spring frost. Overheated plants stop growing, drop flowers and become more susceptible to pests.

• Shade cloth (50–70%) – spread over the roof or inside the greenhouse, shading level can be adjusted as needed
• Shade paint – white preparation applied to glass or polycarbonate reflects sunlight; easily washed off in autumn
• External blinds or film – the most effective solution as it traps heat before it even enters the greenhouse
• Climbing plants – luffas, bean runners or cucumbers grown along the south wall provide natural and productive shading

What to Grow and When – Seasonal Calendar

Spring (March–May)

Month	Seedling Raising (in heated space)	Direct Sowing or Planting
March	Tomatoes, peppers, aubergines, kohlrabi	Radishes, lettuce, spinach
April	Cucumbers, courgettes, squash, melons	Dill, rocket, cabbage turnip
May	Basil, celery	Beans, corn (in polytunnel)

Summer (June–August)

Main season for heat-loving crops – tomatoes, peppers, cucumbers, aubergines and melons. The key to success is regular ventilation, adequate watering and protection from overheating. In tropical heat shorten watering to early morning hours so leaves dry before night.

Autumn (September–November)

Month	Sowing or Planting	Harvesting
September	Lettuce, spinach, corn salad	Tomatoes, peppers (picking)
October	Garlic (in bed)	Last cucumbers and aubergines
November	–	Lettuce, spinach, corn salad

Winter (December–February)

In an unheated greenhouse, frost-hardy crops survive: corn salad, winter spinach, garlic and parsley. In a heated space with minimum temperature around 10 °C you can successfully grow herbs, cut lettuce and microgreens – and begin raising the most demanding varieties as early as February.

Accessories You'll Appreciate

• Growing tables and shelves – efficiently use vertical space and allow raising more seedlings
• Automatic drip irrigation with timer – saves time and prevents uneven watering; choose from watering category
• Digital thermometer and hygrometer with min/max memory – overview of conditions at night and in your absence is invaluable
• Garden textiles – mulching beds inside the greenhouse suppresses weeds, retains soil moisture and slows evaporation
• Gutter and rain barrel – collecting rainwater from the greenhouse roof saves tap water and plants prefer it to chlorinated mains water

Frequently Asked Questions (FAQ)

Is glass or polycarbonate better?

For most gardeners, double-wall polycarbonate is the optimal choice. It has better thermal insulation, is lighter, safer if broken and much more resistant to hail. Choose glass if you want maximum light transmission, prefer classic aesthetic appearance and don't mind the higher weight or breakage risk.

How large a greenhouse do I need for a family?

For a typical four-person family we recommend a greenhouse of 10–15 m². If you plan year-round growing or want plenty of space for seedling raising plus fruiting plants, consider 18–25 m². In the greenhouse selection you will find models in a full range of sizes.

Do I need a building permit for a greenhouse?

Greenhouses up to 40 m² footprint and 5 m height fall under minor structures and do not require a building permit. However, you must maintain a minimum 2 m distance from the property boundary and verify compliance with your local territorial plan.

Is a polytunnel worth it compared to a greenhouse?

A polytunnel is the right choice if you need large covered space for the lowest investment and plan regular film replacement. For professional vegetable growing with emphasis on area, a polytunnel with quality UV stabilised film is an excellent solution. If you seek year-round operation, aesthetics and long lifespan without repeated costs, choose a greenhouse.

How do I prevent greenhouse overheating in summer?

Combine roof vents, side windows, shade cloth and regular watering. Automatic vent openers are affordable and work reliably without electricity. In extreme heat, spraying the floor with water helps – evaporation significantly reduces air temperature inside the structure.

Sources and Further Reading

• RHS – Greenhouses – Royal Horticultural Society, expert guide to growing under cover
• NKZ.cz – Our Beautiful Garden, practical advice for Czech gardeners
• CZECHBUILDINGS.cz – Minor Structures – current information on building regulations and conditions for minor structures