What you need to consider before preparing plants for winter:

• Clean plants before bringing them inside

• Remove all fallen leaves, any withered or diseased foliage, and all dead wood.

• If there are pests on the plant, you need to treat it again. Never bring plants inside for winter with pests on them!

Choose a suitable location:

Light: Deciduous plants can be put away in a dark place for the winter, but evergreens need light. The warmer the location, the more light the plants need.

Temperature: There are three different categories: Plants which tolerate frost, plants which need to stay frost-free, and plants which need to stay warm over the winter. It is best to keep Mediterranean plants in a light place at temperatures of between 10-12 °C over the winter and to water them moderately so that they don't dry out. Keep tropical plants in a light place at a temperature of 20/22 °C and water appropriately so that they are not too wet but stand in moist soil.

And once again: The warmer the location, the more light the plants need!

Assistance: Inflatable greenhouses with frost monitors are now available and make suitable overwintering locations for Mediterranean pot plants if you don't have enough space for them elsewhere.

When should I bring plants inside for the winter?

The basic rule is as follows: 

Try to bring your potted plants indoors as late as possible and reintroduce them outdoors as early as conditions permit. In general, it is preferable for plants to be outside rather than inside, as indoor environments can cause stress for plants due to the deviation from their natural habitat. Certain plants like angel's trumpets, bougainvilleas, hibiscus, and heliotropes need protection from frost and should be safeguarded accordingly. However, flowering maple, bottle-brush, cassia, citrus, tea-tree, and leadwort are more resilient and can tolerate freezing temperatures. Hardy plants such as Japanese laurel, Norfolk Island pine, arbutus, Italian cypress, loquat, laurel, olive, and Italian maple can endure mild frost (around -5°C).

Things to consider about winter quarters for plants:

Maintaining strict hygiene in the winter quarters is essential. Regularly clean your plants, as you did before bringing them inside, at least once a month. Be vigilant for pests starting from the end of January, as scale insects may make their appearance during this time. Spider mites, mealybugs, and aphids can also be potential threats starting from February. Ensure that the winter quarters are properly climate-controlled to maintain the appropriate temperature for overwintering. Consider installing a frost monitor where necessary to regulate ventilation and prevent frost damage. Keep in mind that large glazed winter quarters, especially from early February, can become excessively hot. Avoid exposing overwintering plants to significant temperature fluctuations or premature outdoor exposure.

Information about individual varieties you have asked about:

Agapanthus: Overwinter varieties with leaves in a bright, cool location at a temperature of 5-10°C. Water sparingly to prevent drying out. Varieties that lose their leaves can be overwintered in a dark place without watering. Repot every two years in the spring.

Thorn apple/Angel's trumpets: Bring indoors before the first frost. If the plant has experienced slight frost damage but the main wood is unaffected, it is worth overwintering. Prune minimally to avoid delaying flowering next year. Overwinter in a bright, cool place at temperatures of 2-5°C. Moderate watering for plants with leaves; sparing watering for bare plants to prevent drying out.

Fig tree: Unripe fruit for the following year may be present. Frost-resistant figs in pots can withstand temperatures down to -5°C with proper drainage and wrapping in fleece. Alternatively, store the plant in a garage, providing darkness and some frost exposure. Water adequately to prevent fruit from shriveling. Avoid wild temperature fluctuations to prevent fruit damage.

Gingko: In pots, it is more vulnerable to frost, so storing in a garage is recommended. Alternatively, remove from the pot and plant it in a protective spot in the ground. If kept on a balcony, wrap the pot and plant with fleece (not film!).

Herbs: Parsley, lovage, lemon thyme, etc., can remain in their beds. Curry plants and lavender cotton should be kept in a bright, cool, frost-free place at 5-10°C.

Daisy bush: Prune approximately one-third of the plant before winter. Overwinter in a bright location at 10-12°C, watering moderately to prevent drying out. Repot in fresh soil in spring.

Oleander: Established plants can tolerate slight frost between 0 and -5°C. Keep in a moderately lit location at 5-10°C. Water sparingly, but prevent drying out.

Passion flowers: In mild climates and sheltered locations, passion flowers can remain outdoors. They can withstand temperatures down to -5 to -10°C if well established. Otherwise, bring indoors and overwinter at a temperature of 10-12°C when the outside temperature is between 0 and 5°C. Water sparingly to prevent drying out. Note that different varieties may have specific temperature and moisture requirements.

Citronella plant: Overwinter in a well-lit location at approximately 10-15°C, watering occasionally and moderately.

For a comprehensive guide to overwintering pot and tub plants, refer to the GARDENA gardening experts' publication from 2003 by KOSMOS in Stuttgart.