Garden pansies (Viola wittrockiana) and horned violets (Viola cornuta) show a similarity and are related to each other. They bloom colorfully from spring to autumn. Differences can be found above all in overwintering and frost sensitivity. Everything you need to know about how much frost they can tolerate and what else needs to be considered can be found below.
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A distinction is made between plants that hibernate outdoors in winter between frost resistance and winter hardiness. Frost hardy varieties tolerate frosts around freezing point. They fall into climate zone 10 between plus 4.4 and minus 1.1 degrees Celsius), some specimens just barely reach climate zone 9 if they endure cold temperatures of up to minus two degrees Celsius.
- Plants with winter hardiness fall at least in climate zone 9 with minus temperatures up to a maximum of minus 6.6 degrees Celsius.
- Plants in climate zone 8, which can tolerate minus temperatures of up to 12.2 degrees Celsius, are particularly hardy
- Climate zone 7 includes winter hardiness down to minus temperatures of 17.7 degrees Celsius.
There are no varieties of pansies and horned violets that survive even lower winter temperatures, so that the winter hardiness is over by climate zone 7 at the latest.
Explanation: cold protection
If plants outdoors are sensitive to cold or do not have sufficient winter/frost hardiness, the root area in particular should be protected against the cold. This keeps the frost from getting into the soil, freezing the soil and damaging the roots.
The following materials and measures are suitable as protection against the cold:
- Wrap bucket with foil or fleece
- Place the bucket on an insulating surface such as styrofoam, cardboard or a wooden board
- Cover the earth in a thick layer with one or more materials such as
- pine needles
- Cover plants completely with fleece and allow fleece to run out on the ground above the root area
Pansies hardy or frost-resistant?
Most pansy varieties are frost-resistant or winter hardy. In particular, the perennial/biennial specimens overwinter outdoors. Depending on the temperatures and frost or winter hardiness, the flowers close and open again as soon as the outside temperatures are milder.
Hardy and frost-resistant varieties
- Yellow alpine pansy (Viola lutea) – hardy with climate zone 9 and a maximum of minus 6.6 degrees Celsius
- Swiss giants (Viola x wittrockiana hybrid) – below hardiness zone 9 only with winter protection
- Wild pansy (Viola tricolor) – for climate zone 7 to a maximum of minus 15 degrees Celsius
- Two-Flowered Violets (Viola biflora) – Hardy hardiness zone 10 to slightly below freezing
Pansies in tubs/balcony boxes
If pansies, no matter what variety, are planted in a bucket, the winter hardiness and frost resistance is different. Here, the winter cold penetrates much more into the above-ground soil, so that frostbite damage can occur even in particularly hardy specimens. The basic rule here is to provide insulating protection against the cold as soon as the first frost sets in.
Horned violets hardy or frost-resistant?
Horned violets are used to the low temperatures of their region of origin, the Pyrenees. Accordingly, they get along well with the Central European winter temperatures and the sometimes harsh climate here.
Glycerin against frostbite
The Viola cornuta contains glycerin in its cells. This is the same substance that provides freeze protection in vehicle radiators. It has a similar effect on horned violets and provides comprehensive protection against frostbite. Nevertheless, the different varieties differ in their winter/frost hardiness.
Hardy and frost-resistant horned violets
The least sensitive horned violets are the hybrids. They have a winter hardiness of at least around minus 15 degrees Celsius (climate zone 7). Most of the non-hybrids are not sensitive to frost down to at least minus five degrees Celsius (climate zone 9).
Horned violets in tubs/balcony boxes
As already described under pansies, horned violets in tubs and balcony boxes are also much more exposed to the cold. They should also be equipped with appropriate protection against the cold from the onset of frost.
Cold protection advisable
As a rule, hybrids do not need separate protection against the cold, provided they are planted in the garden bed. For all other specimens, protection against the cold as described above is advisable if the temperatures are below zero degrees Celsius for a longer period of time. They often react more sensitively to permanent frost.
snow for protection
In the case of pansies and horned violets, it is an advantage if they are covered with snow during frost, otherwise they can dry out. This is because the frost would otherwise freeze the area around the roots and as a result they would no longer be able to absorb water. The snow cover on the flowering plants provides a certain amount of protection and also makes a major contribution to preventing dehydration. If there is no snow and it gets freezing cold, experts speak of a frost. However, it should be watered here to prevent dehydration.
Frost becomes a problem for Viola wittrockiana and Viola cornuta , regardless of winter or frost hardiness, when they are immersed in the winter wet and it freezes. The risk is then immense that the roots will be damaged and/or the supply to the plants will be disrupted, which can lead to death. Rain protection is advisable, as well as drainage to improve the drainage of winter moisture. In addition, only water when the soil has dried to minimize the risk of overwatering.