In autumn we are slowly getting ready for the cold season and start to prepare the balcony, terrace and garden for the coming winter. Now is also the time to think about which plants can withstand the cold at all and which can not. But in order to assess this correctly, we need to take into account several factors and clarify a few things in advance – for example, what is the difference between “hardy” and “winter hardy” and what role the location plays in this.
Winter hardy – what does that actually mean?
“Winter hardy” describes whether the plant in question can cope with cold and survive the winter outdoors. However, this can vary greatly from region to region, because “winter-hardy” in Mallorca is something completely different than in deepest Siberia; the winters on our favorite vacation island are known to be not quite as merciless as the Russian ones. If we now buy a “hardy” plant in our Central European latitudes, the term refers to the local temperatures. However, in the trade, in addition to the “hardy” fellows, there are also those that are called “hardy”. These plants can not take on severe frosts, they are just not quite as sensitive to cold and need – whether outdoors or in a container – in any case a shelter in the winter!
The winter hardiness zones
In order to make the whole thing a little clearer, there is therefore a general division of sub-zero temperatures into so-called “winter hardiness zones”. There are a total of 11 of them, which can be differentiated even further among each other (but the coarser classification is enough for us for now). Why all the effort with the different zones? Quite simple: As already mentioned above, in each region the winter can strike with completely different hardness. So these zones help us determine whether or not the particular plant in our area will survive the frost reasonably unscathed. For example, if you read that a plant is hardy up to zone 8, it will tolerate a maximum of about -12°C.
The 11 winter hardiness zones:
Zone 1: below -45.6 °C
Zone 2: -45.5 °C to -40 °C
Zone 3: -39.9 °C to -34.5 °C
Zone 4: -34.4 °C to -28.9 °C
Zone 5: -28.8 °C to -23.4 °C
Zone 6: -23.3 °C to -17.8 °C
Zone 7: -17.7 °C to -12.3 °C
Zone 8: -12.2 °C to -6.7 °C
Zone 9: -6.6 °C to -1.2 °C
Zone 10: -1.1 °C to +4.4 °C
Zone 11: +4.5 °C and higher
Temperature is not everything
While the winter hardiness zones and respective temperatures are a great guide for us, they are not set in stone. External factors, such as location or weather, have additional influence on the damage that can be caused by frost.
For example, freezing cold with bright sunshine can cause plants to dry out because they cannot absorb water through the roots (because it is frozen), but the sun’s rays cause the plant to lose water. Conversely, prolonged heavy rain in cold weather can cause waterlogging and thus root rot. Mulching provides a remedy in both cases, and is thus useful for cold-resistant plants as well.
The location is also important: If a plant stands freely in the area, it will definitely be colder and frostier for it than if it stands in a protected niche or near a house wall, because the latter radiates heat and catches strong winds. And the type of soil also affects how frost affects the soil and plants. Loose and permeable soil causes fewer problems, but very heavy and impermeable soil can also cause waterlogging. Finally, where you live also plays a role – urban environments are often a little milder than rural ones.
Generally, a little more caution is needed with potted plants than with those grown outdoors. Even if the plant that is in the tub is actually hardy, it can suffer frost damage. In the container, the root ball is less protected, which is why cold and frost can attack the plant from all sides. Soon you will find in our magazine described in detail how to properly winter his plants – both in the tub and outdoors!
Finally, we have compiled a few examples of our hardy plants and their non-hardy counterparts for you. Zones 1 and 2 are probably reached in Europe in the absolute exception (as far as frost is concerned, we are fortunately quite spoiled here!), but from zone 3 almost everything is possible.
In fact, there are even a few hardy ones, like our Bloomify Blueberry and Blackcurrant, that can handle low temperatures down to -39.9°C – both have absolutely earned the honorable title of “ice queen”! And if you thought aromatic herbs were no match for the cold, we have a little surprise for you; some fragrant types can definitely take on temperatures as low as -28.8°C (Zone 5). Mint “Mojo”, sage “Salvador” and chives “Siggi” won’t be brought to their knees anytime soon, nor will our Bloomify gooseberries and autumn raspberry “Heidi”. Most fruit trees (for example, our apples “Boskop” and “Elstar”, as well as pear “Biggi”, plum “Paula”, sweet and sour cherries “Karla” and “Karl”) and strawberry “Enno” also belong to the tough guys and can be assigned to winter hardiness zone 6. Not quite as hardy, but still winter-hardy to -17.7°C are, among others, our grapes and coriander – this corresponds to zone 7.
Rosemary, on the other hand, lives up to its reputation as the herb of the Mediterranean countries and is not such a frost fan: with -6.6°C (zone 9) as its tolerance limit, it is more of a warm-weather plant. The real frostbites, which like neither cold nor frost, are our exotics: Citrus fruits, such as the lemon “Zeus”, lime “Lilly” or kumquat “Casimir” can not defend themselves against freezing temperatures (let alone survive them unscathed) and absolutely must move to suitable quarters for the winter. Soon we will publish a nice guide on how best to bring the little trees through the cold season.
I have 30 years of experience and i started this website to see if i could try and share my knowledge to help you.
With a degree a Horticulture BSc (Hons)
I have worked as a horticulture specialist lead gardener, garden landscaper, and of course i am a hobby gardener at home in my own garden.
Please if you have any questions leave them on the article and i will get back to you personally.