Cold hardy cacti in Sweden?
Yes, growing cacti without heating in Sweden is possible even though we have a very harsh climate with often a very rainy, wet autumn and cold winter! At the moment, when writing this, we have - 20 °C here in Skogstorp and 20 cm snow ...
I have grown a handful different species in a rock garden here in Sweden. The plants are not very beautiful after having spent six months with rain and snow but they (mostly) survive!
Where can I place them?
Grow them in a rock garden or an unheated greenhouse. If you grow them in a rock garden, try not to place them on flat ground which can result in that they get drowned during heavy rains. In winter they are best grown under cover. A frame with
glass och plastic takes away most of the rain and keep the plants and their roots drier. It results in more healthy and better looking plants.
In an unheated greenhouse they will stay in a dry place and will resist the cold weather much better. You will also be able to grow many more species in the greenhouse, species which would not like the wet soil outside in the rock garden. It is very important that you give the plants much fresh air. Remove the door so fresh air constantly is circulating. If closed fungus will soon appear.
If you want protection from the most heavy rains and coldest winds - plant them close the house ground.
To protect plants during winter in your rock garden, especially if you grow in an humid area with much rainfall, you can
make a simple frame with a plastic (or glass) sheet.
Sand, gravel and a little humus. Good drainage is a MUST!
Not necessary but they do look finer and grow better.
Which species can survive here?
Below I have tried to list some of the most tolerant species.
One of the best species is Escobaria missouriensis which is a plant native to central and north USA. It can survive very low temperatures, at least down to -25 C, and without any protection at all. I have had a few plants in flower too, and they are cream-white. The variety v. caespitosa is similar but can form large group of small heads.
Escobaria vivipara (left) is another species which I have been quite successful with, even though it does not grow very fast in my rock garden. You can find it from south-east USA up to Canada where it spends the winter often covered by snow! It is a small globular plant with many, multicoloured spines on tubercles. The flower appear on top of the plant and is violet-pink.There are several varieties to this species; v. arizonica, v. bisbeeana, v. buoflama, v. kaibabensis, v. neomexicana and v. rosea. They differ in spines and flower and are all hardy. There are other hardy species of Escobaria as well, but they are a little bit tricky if kept to wet. E. leeii and E. sneedii are two very beautiful species from New Mexico, USA with dense white spination and small pink flowers. They form large clumps of small heads and flower easily. The only problem is their tender root system. If they are overwatered they will rot so they are best grown in a mineral mixture without any humus. I do not think they can be grown without protection in Sweden, but in an unheated greenhouse they will do fine. Other species suitable for unheated greenhouse are E. albicolumnaria, chaffeyi, duncanii, hesteri, minima , organensis, robbinsorum, roseana and tuberculosa.
Try Echinocereus viridiflorus, a tiny species from the States with red-white spines and many small, lemon-scented flowers. It is an extremely hardy plant which can be grown almost everywhere - if you select a good clone! It is a wide-spread species and SuccSeed has seeds from some of the best and coldest localities. I have grown this species without any protection and 2 year old seedlings survived rains and -20 °C without problem.
Echinocereus triglochidiatus is a groupforming species which vary a lot from place to place. It can form very large groups of heads with long and beautiful spines. The flower is reddish and stays for a week or more if it is not placed too hot. There are some varieties which are also very hardy and suitable for the rock garden; v. mohavensis and v. mojavensis. Similiar is E. coccineus with nice spines and red flowers. Other Echinocereus to grow outdoors or preferably in an unheated greenhouse are; E. chloranthus, russanthus (both small and cylindrical with small, scented flowers), E. dasyacanthus, engelmanii and especially the var. variegatus, E. fendleri with varieties, E. papillosus, E. pectinatus, E. perbellus, E. reichenbachii, and E. stramineus.
Opuntia is a very large and widespread genus which can be found from Argentina up to Canada. Many species growing on in the United States and Canada are cold hardy and also suitable for European rock gardens or an unheated greenhouse. I have tested a handful different species with quite good result. Opuntia fragilis is a variable species and usually has small cylindrical segments and 1-2 cm long spines. It is very hardy and can survive as low temperatures as -60 C! Other nice species are O. gilvescens, O. compressa, O. imbricata, O. phaecantha, O. viridiflora and O. whipplei.
||Pediocactus simpsonii SB 877 flowers early in spring with pink to white flowers. Buds are usually developed in autumn. Likes a cold winter and spring. Do not expose it to overheating in spring as the buds my dehydrate.
Pediocactus species like P. simpsonii are well-known to be very cold resistant plants. They grow in New Mexico, Utah, Oregon and other states with low winter temperatures. It is a very variable, spiny and globular plant with white to pink flowers. They flower early in the spring, here in Sweden often in April-May. All Pediocactus are a bit tricky to survive outside here in Sweden. Not because of the low temperatures but due to humidity. Kept in a greenhouse without heating they will do well, and flower without problem if not standing in a too hot place when developing the sensetive buds. Highly recommended plants but not as easy as for example Escobaria, Echinocereus and Opuntia!
||Echinocereus viridiflorus (Union Co, NM) flowering in my rock garden! This is a very hardy and easily grown species.
||Escobaria missouriensis survive almost everything! Rain and cold does not stop this species!