Nothing quite epitomizes the “Wild West” like cacti, although sagebrush and the notorious tumbleweed come close. Like the latter plants, throughout much of the west certain kinds of prickly-pear cacti (genus Opuntia) have taken over vast expanses of what were once grasslands and are considered by many to be pests. Severe overgrazing during the 19th Century led to this catastrophic range degradation; a period of American history that we tend to romanticize, just like Paul Bunyan romanticizes this same period of exploitation and ecological collapse in my region. No, I do not think of this when I look at my cacti. I see beauty and variation, toughness, and adaptability. There is nothing else on the planet that I can grow here that looks like them. As a child vacationing in Colorado, I was fascinated by the spiny clumps of cacti (Opuntia polyacantha) which my dear aunt, unfortunately, put her hand into as she was climbing the wall of Big Thompson Canyon near Estes Park. 
So how do I do it? How is it that I am able to grow cacti near balsam firs in a Northwoods clearing? Well, as I mentioned, they are tough and adaptable, unlike many other typically western plants. Growing them has certainly been a process of trial and error, with some thorough research into their particular needs thrown in. Before planting cacti, a suitable site must be either found or created. Not all cacti favor the same location. Prickly-pears and cholla in the genus Opuntia tend to do best on fairly level to gently sloping terrain, while the hedgehog cacti (Echinocereus), ball cacti (Escobaria), and snowball cacti (Pediocactus) require sharply drained sites such as the south face of a rock wall for long-term survival. For all kinds, it is vitally important to prevent water from accumulating on the soil in the wintertime. I have grown and killed many cold-hardy cacti, from Gymnocalycium to Sclerocactus. They all succumbed to that “hardy in Denver” temptation which draws in eastern rock gardeners like the song of the lorelei. And it is not just cacti: fully hardy delospermas and agaves tempt us over and over, never to attain lasting satisfaction. Now we know what those poor male bees must feel like being tricked by bee orchids! The only time these cacti and others overwinter here is when the soil stays relatively dry beneath the snow. That does not happen very often. Inevitably they turn to mush after being deeply buried beneath wet snow for five months.
Here in the Northwoods, there are several unpleasant ways for a cactus to die related either to cold or moisture. The part of a cactus exposed above the snowline can be killed by extreme cold because it was simply not hardy enough for our climate. After all, my cactus bed and I have experienced -42°F (-41°C). Well, sort of. They were covered in snow while I had insulated clothing on. Cold can also damage or kill the plants if they fail to harden off in time for the first hard freeze. This can befall some after we experience an unusually cool and rainy growing season.
Too much wetness during winter can suffocate or drown cacti. At any time of year, it is vitally important to promptly remove fallen leaves and other detritus from on and around the plants because, when wet, they will smother them like a plastic bag. Living in the woods, my opuntia bed is subjected to a constant rain of debris. Thus, of all my beds, this one requires by far the most maintenance. I strongly advise anyone who is considering growing cacti in the east to keep the beds small and manageable. The raised beds should only be wide enough so that you can easily reach in with tongs from either side. Strategically place large protruding rocks so that you can lean a hand or knee on them as you work. 
Cacti should be located in the hottest, sunniest part of the yard. When I started to build my opuntia bed, I first ringed the perimeter with larger rocks and then filled it in with load after load of coarse glacial sand, sans organic debris, to create a raised bed. Grains of glacial sand have uneven surfaces, unlike beach sand, allowing water and oxygen to pass through. Stones are a cactus gardener’s friend. A mulch of various sized stones fitted together will keep weeds to a minimum and prevent rain from splashing sand onto the cactus pads. In our northern clime, darker stones are preferable as they absorb heat. The lighter ones can be saved for an alpine bed. I have also learned that a ground cover of spikemosses such as Selaginella rupestris or S. tortipila can serve the same purpose. In the east, wild prickly-pears are commonly found growing within mats of these spikemosses. 
Here in the Northwoods, it is difficult to provide the good air circulation that cacti crave, so some are beset by fungal infections from exposure to prolonged periods of rain or dew. Certain cacti appear immune, while in others the infections are minor, with the fungal invasion promptly walled-off. By far the most serious is a fungus which, unbeknownst to me, arrived with pads gifted to me by another Midwestern hardy cactus enthusiast. It is the cactus version of trench foot or leprosy, except that this is highly contagious. I call it the “Black Death,” for the initial black spots enlarge and, if not excised, will consume all or most of the pad. If uncontrolled, the infection load is so great that it can even overwhelm the defenses of cacti which are normally immune. Before I realized it, my original opuntia collection was virtually wiped out. A couple of years ago I thought I had eliminated it, but this year it showed up again, apparently from a hidden reservoir at the base of a pad. Please take my advice and excise any sign of infection in a new cactus so that you don’t end up with the gift that keeps on giving. A scalpel and tongs are the tools of choice. 
After all that, you might think hardy cacti are difficult to grow. On the contrary, I find them relatively easy. They are one of the simplest plants to propagate. Just cut off a pad or head, let it sit in a dry place for about a week to heal over, then plant it out. Each of my prickly-pear pads is planted about one-third into the sand, but I have seen other gardeners simply lay Opuntia humifusa pads on the ground where they root nicely. The severed heads of other kinds of cacti are wedged into crevices containing a bit of soil in the face of our rock wall. Many of my cacti were grown from mail-order seed. That is really fun but super-slow. I plant them indoors in June (long warm days, air circulation from open windows) in packs filled with our coarse glacial sand. Once the seedlings are well-developed, I cut down watering to once a week. By the latter part of October, they have gone dormant and watering ceases entirely. Once the packs are bone-dry, I bring them down into the root cellar for the winter. Then at the beginning of March, I bring them up to the windowsill once again and water them thoroughly once a week. An occasional application of a balanced liquid fertilizer will do wonders. By June they will be ready to plant out, at a mere 0.25-0.5 inches (0.6-1.2 cm) tall. Harden them by placing them outdoors in semi-shade for a week before moving them into full sun. Yes, even cacti will sunburn!  
Propagating cacti offers the added bonus of meeting great people to swap with, or scrolling thru some eye-catching online catalogs. If you plan on growing cacti of western provenance in the east, it pays to inquire whether the cuttings or seeds were originally from regions of moister climate, relatively speaking. Those from much of Colorado and points north and east tend to do well here in Wisconsin. The same species from New Mexico and the sky islands of Arizona will not survive here in the long term, as they are intolerant of prolonged winter wetness. Cacti from Nevada and Utah have never survived the winter for me.
There are four genera of cacti which I successfully grow, with certain species which have, over the decades, proven themselves fully hardy. These genera are Echinocereus, Escobaria, Opuntia, and Pediocactus. Let’s start with the straightforward ones. My single snowball cactus, Pediocactus simpsonii var. minor, is happily perched on the face of the rock wall. In the wild, they often bloom when there is still snow on the ground, hence the name. It is a Minnesota self-sown seedling of a plant that originated in Colorado. There they can be found up to 11,000 feet (3,353 m) with winter temperatures down to at least  -52°F (-47°C). It is the earliest cactus to bloom here, typically in May. Other individuals of this species from Colorado did not survive their first winter, much to my dismay, even though they were planted near my original one. I suspect that their provenance was from an unsuitable environment, as they inhabit a wide ecological range. Snowball cacti reportedly require even sharper drainage than most hardy cacti, acidic soil, and cool summer nights, which explains why it is happy where it is. 
Numerous ball cacti, Escobaria vivipara, are thriving in the face of the rock wall. All are from the native population in western Minnesota which occurs in an area of less than 2.5 square miles (6.5 square km). They bloom spectacularly in June and afterward offer juicy, delicious fruits. The Minnesota form is the only one that is reliably hardy here, even though ball cacti can be found growing wild in Alberta and Manitoba and up to 8,000 feet (2,438 m) in the U.S. The western varieties do not survive their first winter and even plants from central North Dakota were killed by a recent wet winter after doing well for two decades. None survive here on nearly level ground. I grew a couple of Missouri pincushion cacti, Escobaria missouriensis, for many years on level ground until a particularly wet winter did them in. The species is found from North Dakota southwards. It would be great to find a source and attempt to grow them again, this time in the rock wall. 
Echinocereus are my passion and my heartache. I have grown hundreds of seedlings of various sub-zero (-18°C) hardy species and their varieties over the years, with merely a handful surviving. Harsh natural selection at its finest! Two kinds are the surviving champions. Several claret cups (Echinocereus triglochidiatus) are doing well in both the rock wall and, surprisingly, in sharply drained level sites. After seeing how well a plant survived the past wet winter in the latter site, I planted out several more seedlings this summer. These should be particularly well adapted since the seed was collected at 8,430 feet (2,569 m) in central Colorado. I am anticipating both the spectacular flowers and the delicious fruits (hence the other name strawberry hedgehog). A large flowering clump in the wild (to 5 feet/1.5 m across!) can reportedly be seen from half a mile (0.8 km) away. Our hummingbirds are certainly anticipating the flowers too. One of three Comanche lace cacti (Echinocereus reichenbachii subsp. comanchensis) of southwestern Oklahoma provenance has survived and thrived on the edge of the opuntia bed. If it continues to thrive, I may need to change the name of this bed. The green pitaya (Echinocereus viridiflorus), found as far north as South Dakota, is generally accepted as the hardiest member of the genus. Its flowers here were deliciously lemon scented. It has never survived for me very long since it is intolerant of wet winters. That puts it at a distinct disadvantage, as its prairie habitat may not have the prolonged wet snow cover that we do.
Finally, we come to the genus Opuntia, the prickly-pears and chollas. Once I naively thought that I had a pretty good handle on the different species, but now it just seems to be a taxonomic rat’s nest. Simply visiting a single wild population and seeing the awesome variability that can be present makes me throw up my hands in dismay. And joy. Granted, I am not a taxonomist. My interests lie more with plant communities and ecology. So, I’ll not go down this rabbit hole and instead will defer to the experts (“lumpers” or “splitters”?) to sort out this complex mess, ideally with the help of biochemical analysis. What is certain is that prickly-pears can be divided into two main groups: those with fleshy fruits and those with dry fruits. Their fleshy fruits, adapted to passing thru digestive tracts, are known as “tunas” and have a delightful raspberry-watermelon flavor. 
For the sake of simplicity and my own sanity, I have lumped my hardy prickly-pears into four basic types: common prickly-pear Opuntia humifusa and New Mexico prickly-pear O. phaeacantha with fleshy fruits, in contrast to plains prickly-pear O. polyacantha and brittle prickly-pear O. fragilis with dry spiny fruits. The latter group is the northernmost cactus in the world (see my other article on page 417). The Opuntia humifusa group includes the eastern forms which are found in all states east of the Mississippi River as well as western types such as O. macrorhiza, O. cymochila, O. pottsii, and O. tortispina. They are among the most adaptable cacti to our northern clime, having even naturalized in Siberia. Like almost all hardy prickly-pears, the pads wrinkle and contract as they lose water in preparation for freezing weather; otherwise ice crystals would puncture the delicate cell membranes. 
On the other hand, the Opuntia phaeacantha group, which includes O. camanchica and O. gilvescens, do not wrinkle and many do not lay down in preparation for winter. Therefore, they tend to be less hardy, although more ornamental. They have the largest pads of the hardy prickly-pears. Reportedly, they can be found north to Wyoming and South Dakota. None of the many commercially available “hardy” forms are in fact hardy here. The cuttings which I had collected in Colorado all came thru their first winter here in perfect shape, as we were blessed with an early spring. The second winter, however, brought a snowpack that lasted into May. That resulted in the loss of about two-thirds of my plants. It’s okay though, as I do love seeing natural selection in action. Oddly, all plants originating from a northern outlier population near Boulder, Colorado, perished.
Opuntia polyacantha is typically extremely spiny and can carpet the ground for endless miles on some plains, although it does grow to an elevation of 9,300 feet (2835 m). Its range extends from Alberta to Manitoba, and southwards. It is a highly variable group with numerous supposed varieties, many of which possess outstanding beauty even when not in bloom. In some forms, the wrinkled pads take on a gorgeous purple hue in winter due to the presence of anthocyanin pigment which imparts even greater cold tolerance. The smallest of all can be found in the O. fragilis group whose pads are only loosely connected to one another. I have tentatively lumped in the western O. x debreczyi (formerly O. rutila), even though its pads tend not to detach readily and it possesses some other O. polyacantha characteristics.
Chollas are similar to the brittle prickly-pear in that they have barbed spines that cling to passers-by. They differ in their cylindrical stems. I have tried many species, but only one form of one species has proven itself here in the long-term: the prostrate form of Whipple’s cholla (Opuntia whipplei), also called the rat-tail cactus. It is native mostly at higher elevations from southwestern Colorado (the Colorado Plateau) southwards, growing up to 8,000 feet (2,438 m). Its pencil-thick stems form an exotic-looking mat, resembling what artists once imagined as the vegetation on Mars.
My trials and errors will hopefully encourage more gardeners to take a stab at growing cacti in supposedly unsuitable climates. Cactus beds this far north are a great conversation starter.

Tried that, killed that:  
Cold-hardy cacti which did not survive the cold, moist environment of northern Wisconsin

Acanthocalycium violaceum
Austrocactus bertinii
Corrycactus melanotrichas
Denmoza rhodacantha
Echinocactus xeranthemoides 
Echinocereus adustus
E. chloranthus 
E. chloranthus cylindricus
E. chloranthus cylindricus ‘Corellii’
E. chloranthus russanthus
E. coccineus
E. coccineus gurneyi
E. coccineus roemeri 
E. coccineus var. toroweapensis
E. dasyacanthus 
E. delaetii
E. engelmannii var. chrysocentrus 
E. engelmannii var. variegatus
E. fendleri
E. fendleri var. kuenzleri
E. fendleri ‘Odessa’
E. fendleri var. nova
E. fendleri x lloydii
E. fendleri x reichenbachii var. albispinus
E. knippelianus var. reyesii
E. laui
E. ledingii 
E. pectinatus var. rigidissimus
E. polyacanthus
E. reichenbachii
E. reichenbachii ‘Oklahomensis’
E. reichenbachii var. albispinus
E. reichenbachii var. baileyi
E. reichenbachii var. baileyi ‘Minor’
E. reichenbachii var. baileyi albispinus
E. reichenbachii var. baileyi brunispinus
E. reichenbachii var. caespitosus
E. reichenbachii var. minor
E. reichenbachii var. perbellus
E. reichenbachii var. perbellus robustior
E. reichenbachii purpureus
E. reichenbachii var. nova
E. x roetteri
E. triglochidiatus var. mohavensis
E. triglochidiatus var. mohavensis inermis
E. triglochidiatus var. subnudus
E. viridiflorus 
E. viridiflorus var. cylindricus
E. viridiflorus var. davisii
Echinomastus intertextus var. dasyacanthus
Echinopsis bridgesii
E. leucantha
E. silvestrii
Epithelantha micromeris
Eriocyse curvispina
Escobaria echinus
E. minima
E. missouriensis (thrived for many years.  Worth trying again with better drainage)
E. orcuttii var. koenigii
E. organensis
E. sneedii var. albicolumnaria
E. vivipara var. arizonica
E. vivipara var. bisbeeana
E. vivipara var. neomexicana
E. vivipara var. rosea
Ferocactus haematacanthus
F. pottsii alamosensis
F. wizlizenii
Glandulicactus wrightii
Gymnocactus beguinii ‘Senilis’
Gymnocalycium baldianum
G. bruchii
G. bruchii var. calochlorum
G. bruchii var. calochlorum proliferum
G. chubutense
G. gibbosum var. chubutense
G. gibbosum var. nigrum
G. multiflorum
Hamatocactus setispinus ‘Hamatus’
Lobivia aurea var. dobeana 
L. aurea var. leucomalla
L. aurea var. shaferi
L. aurea var. sierragrandensis
L. chrysantha
L. ferox
L. haematantha
L. jajoiana var. paucicostata
L. thionantha var. variiflora
Maihuenia poeppigii 
M. tetuehelches
Maihueniopsis darwinii var. andicola
Mammillaria hesteri 
M. heyderi 
M. heyderi var. bullingtoniana
M. meiacantha
M. sneedii 
M. sneedii var. leei
M. (Coryphantha) tuberculosa
M. wrightii
Notocactus submammulosus
Opuntia aurea 
O. aurea var. nicholii 
O. basilaris var. brachyclada 
O. clavata
O. echinocarpa
O. engelmannii var. texana 
O. fragilis ‘Barr’s Pink’
O. fragilis x polyacantha
O. gilvescens
O. humifusa var. macrorhiza stenochila 
O. humifusa var. robustior
O. kleiniae
O. leei (killed at -27F)
O. leptocaulis
O. littoralis var. martiniana
O. imbricata
O. imbricata ‘Twisted Sister’ 
O. macrocentra
O. nicholii
O. ‘Peter Pan’
O. phaeacantha ‘Mesa Melon’
O. phaeacantha ‘Mesa Sky’
O. phaeacantha ‘Plum’
O. phaeacantha var. camanchaca
O. phaeacantha var. discata
O. phaeacantha var. major
O. phaeacantha x polyacantha
O. phaeacantha x polyacantha ‘Persimmon’
O. phaeacantha x polyacantha var. erinacea
O. polyacantha ‘Crystal Tide’ (killed by yucca leaves & ants)
O. polyacantha ‘Nebraska Orange’
O. polyacantha var. erinacea columbiana
O. polyacantha var. erinacea utahensis ‘Black Knight’
O. polyacantha var. erinacea ursina
O. polyacantha var. trichophora ‘Grizzly Bear’
O. pyrocarpa
O. pyrocarpa ‘Floragrande’
O. sanguinocula
O. tunicata var. davisii
O. violacea
O. viridiflora
O. whipplei, upright form
O. whipplei x imbricata
Pediocactus robustior
Pyrrhocactus andreaeana
P. strausianus
Rebutia spp. mix
Sclerocactus cloveriae
Trichocereus candicans
T. formosus
T. lobivioides ‘Purpureominiata’