Heated & Unheated Greenhouses

Heated & Unheated Greenhouses

The range of plants that may be grown in a greenhouse or conservatory depends mainly upon whether they are heated or not, and if they are heated, the temperature at which they are maintained.


Unheated greenhouses or conservatories are termed as 'cold' and may be used for the following purposes:

  • Extending the growing season of hardy and half-hardy plants.
  • Propagating cuttings.
  • Overwintering slightly tender plants.
  • Growing summer crops.
  • Growing alpine plants.

Shading may be required over the summer and insulation may be needed during winter to keep out the worst of the cold. A good ventilation system is essential throughout the year.


Heated conservatories and greenhouses provide a much more flexible growing space for plants and allow a far greater range of gardening tasks to be carried out. Temperatures can be maintained using an electric heater with a thermostat, set to come on automatically whenever the temperature drops below a specified level. Our article on using heat to create the right growing conditions in a greenhouse or conservatory discusses heating systems in more detail.

The heat may be varied to 3 major levels depending on how you intend to use the greenhouse.

1. Cool or Frost Free

Daytime temperature: 5-10°C (41-50°F)
Night time temperature: 2°C (35°F) or more

These temperatures ensure a frost-free place in which to overwinter tender species. Frost-free greenhouses may also be used to grow all the types of plants kept in an unheated structure (see above), and seeds may be germinated with the aid of a propagator.

As with unheated greenhouses, shading will be needed in summer, insulation in winter, and ventilation all year round.

2. Temperate

Daytime temperature: 10-13°C (50-55°F)
Night time temperature: 7°C (45°F) or more

A temperate greenhouse is useful for growing vegetables and tender, half-hardy and hardy pot plants. A propagator may be used to grow seedlings, or the heat may simply be boosted during that time. Shading and good ventilation will be necessary, especially during the summer.

3. Warm

Daytime temperature: 13-18°C (55-64°F)
Night time temperature: 13°C (55°F) or more

A warm greenhouse will allow you to grow a wide variety of species, such as fruit, vegetables and tropical plants. Seedlings may also be grown without the need for propagation equipment. Good ventilation will be necessary during the summer, along with a system of shading. Artificial lighting may be needed for some parts of the year.