Winter poses particular challenges for gardeners, especially when it comes to protecting frost-sensitive plants.
While some plants overwinter outdoors without any problems, many plants need special protection from the cold, snow and frost.
A greenhouse is an ideal solution for overwintering sensitive plants and getting them through the cold months in good health.
But how exactly does overwintering in a greenhouse work and what precautions should be taken?
In this blog post, you can find out everything you need to know about overwintering plants in a greenhouse.
1 Why overwinter plants in a greenhouse?
Not all plants are hardy.
While native plants such as some perennials or shrubs can often cope well with the cold, many ornamental or potted plants need frost-free conditions to survive.
Mediterranean plants such as olive trees, citrus plants or bougainvillea, for example, are very sensitive to the cold.
A greenhouse provides the ideal protection here, as it generally offers warmer conditions and protects the plants from direct frost, wind and moisture.
2. choosing the right greenhouse
There are various types of greenhouses that are suitable for overwintering plants.
Care should be taken to ensure that the greenhouse is insulated and can maintain a constant temperature.
Here is a brief overview:
SunGarden Select
The double-skin sheet or twin-wall sheet with a thickness of 10 mm has the best insulating properties (3/3) and also scores highly in terms of light transmission (2/3).
SunGarden Infinity
The light-flooded flat roof greenhouse with clear acrylic glass is the best choice for overwintering plants.
All points are achieved in terms of both insulation and light transmission.
SunGarden Modern
With its tinted acrylic glass, this greenhouse has the same insulating properties as the SunGarden Infinity.
Only the light transmission is slightly reduced by one point.
SunGarden Deluxe
The frosted toughened safety glass does not have good insulating properties and you also have to compromise on light transmission.
SunGarden Power
Our Power flat roof greenhouse with strong double glass solar modules on the roof and tinted acrylic glass panes in the walls differs from the Energy greenhouse in terms of light transmission, where only 1 point out of a possible 3 is achieved.
We would recommend our plant lamps for overwintering in this house.
Depending on which plants you want to overwinter, you should choose the right greenhouse.
Additional insulation, such as special foils or thermal sheets, can help to keep the temperature inside stable.
3. preparing the greenhouse for the winter
Before you bring your plants into the greenhouse, a thorough cleaning is essential.
Old leaves, dead plant debris and dirt should be removed to prevent pests and diseases.
It is also advisable to clean the greenhouse windows thoroughly to let in as much light as possible.
Here are some further measures to prepare the greenhouse:
- Check the ventilation:
In winter, good ventilation is particularly important to prevent mold growth and waterlogging.
Make sure that your greenhouse is aired regularly to ensure sufficient air circulation. - Install heating:
Depending on the type of greenhouse and the plants to be overwintered, it may make sense to install heating.
There are various options here, such as electric heaters, gas heaters or paraffin-based solutions.
A greenhouse heater with a thermostat is ideal for keeping the temperature constant. - Additional lighting:
As the days are significantly shorter in winter, it may be necessary to integrate artificial light for certain plants.
Plant lamps with a broad light spectrum help to compensate for the lack of light and support plant growth.
4. which plants can overwinter in the greenhouse?
Not all plants need the same protection in winter.
Below is an overview of the most common plants that can overwinter in the greenhouse:
- Mediterranean plants:
These include olive trees, citrus plants, figs or lavender.
They require frost-free conditions and cope well with temperatures around 5-10 degrees Celsius. - Tropical and subtropical plants:
Banana plants, hibiscus and orchids belong to this group.
These plants require higher temperatures of at least 15 degrees Celsius and can only overwinter in a warm house. - Potted plants:
Many summer flowers such as geraniums, fuchsias or angel trumpets do not tolerate frost and should spend the winter in a greenhouse. - Exotic plants:
Plants such as bougainvillea or passion flowers should also be kept frost-free in the greenhouse.
5. care of the plants in winter
Overwintering in a greenhouse is not only a question of the right temperature, but also requires regular care.
The following points should be observed:
- Watering:
Plants also need water in winter, but in much smaller quantities.
Only water when the soil is dry and avoid waterlogging, as this can lead to root rot. - Humidity:
The air can become very dry, especially in heated greenhouses.
However, tropical plants require a high level of humidity.
Humidifiers or regular spraying of the plants with water can help here. - Pest control:
Pests can also spread in the greenhouse in winter.
Check your plants regularly for pests such as aphids, spider mites or whiteflies and take countermeasures if necessary.
6 Special challenges: Mold and frost
Mold and frost are the biggest challenges that can occur when overwintering plants in a greenhouse.
However, both problems can be prevented by taking the right measures:
- Mold growth:
Mold is mainly caused by excessive humidity and poor ventilation.
Ventilate your greenhouse regularly and reduce watering.
If mold does form, it should be removed immediately and the affected plants treated. - Frost protection:
Even if the greenhouse generally offers warmer temperatures, frost can still occur in extreme sub-zero temperatures.
In this case, we recommend using frost monitors or thermostat-controlled heaters that automatically supply heat when the temperature drops below a certain threshold.
7 The right time for overwintering and wintering out
The time for overwintering depends on the plant and the region.
As a rule, the plants should be brought into the greenhouse as soon as the night temperatures consistently fall below 10 degrees Celsius.
We have calculated the heating requirement and heating load for our greenhouse and can recommend using a 2 – 2.5 kW fan heater with a simple frost monitor.
This allows you to heat the temperature to +5° C even at minus 12° C, regardless of the size, and ensures that the plants can overwinter ideally.
The heating load is of course dependent on the size of the house; for greenhouses up to 10 m2, a heating load of approx. 1.7 kW is sufficient.
In spring, when the temperatures rise again, the plants can gradually be taken out of the greenhouse.
It is important to gradually acclimatize them to the outside temperatures to avoid a temperature shock.
Conclusion
Overwintering plants in a greenhouse is an effective way of protecting sensitive plants from frost and cold.
With the right preparation, a well-insulated greenhouse and careful care, your plants will make it through the cold season in good health and be ready to take off again in spring.
Remember to ventilate your greenhouse regularly, maintain a constant temperature and combat pests at an early stage.
This will create the ideal conditions for your plants to overwinter.
Especially for passionate hobby gardeners, the greenhouse is a valuable support for enjoying the garden even in the colder months.
Whether Mediterranean potted plants, exotic ornamental plants or tropical plants – with the right care and the right precautions, you will be able to enjoy your plants again next summer.
