Buying and Growing Winter Hardy Cactus

Yes, it is easy to grow a cactus outdoors in almost any climate.  Most people know that cacti grow in warm, arid (dry) climates, and most people decide to grow theirs in pots on a windowsill.  People in warm climates often plant them right in the ground outdoors year-round.  Some growers in cold climates take cacti out in the summer and sometimes even sink the pots in the ground for the warmer months.

These are easy methods and this guide is not for those who wish to mimic any of the methods I have mentioned already.  This guide will tell you how to buy and grow a cactus outdoors in a cold climate, and leave it out there all winter to survive, grow, and thrive for decades!  It's just like growing in California, except I do it in Michigan.  Here is what you need to know:

Selecting Hardy Species

Nomenclature

Nomenclature is just a fancy term that means the naming of plants.  You need to know genus (plural genera) and species.  You are probably familiar with many genera even if you don't know the Latin: Quercus (oak trees), Acer (maple trees), Taxus (yews), Pinus (pines), Yucca (yuccas), Hosta (hostas), Hemerocallis (daylilies), Papaver (poppies), Cannabis (hemp), Canna (cannas), Musa (bananas), are all plants; Morchella (morel mushrooms); Sialia (bluebirds), Iguana (iguana lizards), Canis (dogs, wolves, coyotes, jackals) are all animals.  A genus is a closely-related group of species.  Usually, the genus name is just the Latin name (canis) for the same thing in English (dog).  Often we use the genus name in everyday use, as in Canna, Yucca, Hosta, Iguana.  Get the idea?  You will need to learn a few genera of cacti.  This is because many cacti don't have common names, and most people are not familiar with various species.  Therefore, the only way for all of us to know which cactus is which is to use the scientific nomenclature.

Common Genera which include Hardy Cacti:

• Opuntia - Prickly Pears and Chollas (pronounced CHOY-yahs)
• Echinocereus - Hedgehog cacti
• Coryphantha - Ball, Beehive, or Pincushion cacti (Coryphantha, a.k.a. Escobaria, Neobesseya, and Mammilaria)
• Pediocactus - no real common name but sometimes called Pincushions
• Sclerocactus - Claw or Devil's-Claw cacti

                       Opuntia imbricata (cholla)                   Echinocereus viridiflorus        Echinocereus baileyi v. caespitosus              Coryphantha vivipara

There are a couple pet peaves people have about nomenclature.  I don't want to get into them much other than to tell everyone to just get over it.

• Proununciation of Latin names - Latin is called a dead language by many who teach it (!) and therefore there is no "correct" pronunciation for any Latin plant name.  Most of these names were created in the last 150 years, long after Thomas Jefferson and his buddies stopped talking in Latin or any other language.  If you really must know how to pronounce Latin words, ask a classical scholar, and then see if the local Catholic priest really cares how you pronounce Echinocereus!
• Lumping and splitting - One species can become eight or so species, and vice versa; one genus can become eight or so genera, and vice versa.  I don't care whether some are called species or varieties.  The only reason you should invest emotion and blood pressure in this issue is if you are concerned with the Endangered Species Act.  Otherwise, a species is just the opinion of a botanist.  All these names are just creations of humans so we can manage volumes of information.  Don't sweat it!  Just remember a few variations.

Hardy species

All of the following are commonly refered to as winter-hardy cacti for cold climates.  They are generally good for zones 5 to 8.  Many are hardier for cold winters, like Opuntia fragilis which will probably grow into zone 2 or 3.  It grows into the northern plains of Canada near the Peace River, within a couple hundred miles of the Arctic Circle!  That's cold!  These are the most commonly-known winter-hardy cacti:

• Opuntia: Opuntia humifusa, O. compressa, O. macrorhiza, O. polyacantha, O. basilaris, O. fragilis, O. erinacea, O. phaeacantha, all prickly pears; O. imbricata, O. whipplei, both chollas.
• Echinocereus: Echinocereus baileyi, E. reichenbachii, E. triglochidiatus, E. viridiflorus, E. engelmannii, E. fendleri.
• Coryphantha: Coryphantha vivipara, C. missouriensis, C. sneedii, C. leei.
• Pediocactus: Pediocactus simpsonii, P. nigrispinus.
• Sclerocactus: Sclerocactus parviflorus, S. whipplei.

Finding the Plants

This is very easy on Ebay!  Just search for "winter hardy cactus" or "Opuntia humifusa" (or any name above).  A great feature I found is to use an asterisk (*).  If you don't know whether the seller will list the plant as "Opuntia polyacantha" or "O. polyacantha", or if the seller accidentally misspells "polyacantha", then you can search for "op* poly*" and you will probably get cacti, as well as some other weird stuff like sheet plastic with an "op" specification.  The advantage is that you won't miss any Opuntia polyacantha cactus.

It is best to start out with cacti from the genus Opuntia, and specifically the prickly-pears.  They are the toughest plants.

If you don't know if the plant is hardy for your area, then ask the seller, or check for "item location."  Another advantage is that the prickly-pears are easy to root and hard to kill.

Growing the Plants

Planting

If you have purchased an Opuntia cutting, all you have to do is set the cutting on dry ground.  Dry ground is any ground which does not get flooded.  For a prickly-pear, this means dropping it or lying it down, concave side up.  This way the plant will not be set back by sunburn.  You can sink the stem into the ground if you prefer the plant to begin growing more upright, but this will make little or no difference after a year or two.  For a cholla, this means to stand up the cutting.  It may grow from the tip, or it may grow from the bottom.  Let it do its own thing.  It will grow faster that way.

If you get Opuntia cuttings consisting of more than one segment, then it is best to split it into individual segments before rooting.  Smaller cuttings establish most easily.  Large rooted plants dug from where they were growing are the most difficult to establish.  A small cutting will have more living branches and be more massive after 5 years than the largest transplant.  I have seen transplanted chollas that just get smaller every year.  Mine grow larger every year, and are really getting to look like cactus wrens will nest in them.  Too bad the cactus wren is 700 miles away!  Be sure to let the cut-wound heal over 2 or 3 days before exposing it to weather or soil, to avoid rot.

Precautions

• Spines and Glochids - Be sure to use tongs, not gloves, to handle any cactus.  Both spines and glochids (very tiny spines) are barbed at the tip, but the glochids detach easily in the skin and are the nastiest part of an Opuntia cactus.  They lodge into the skin and cause irritation for a long time.  They go in easily and are hard to get out.  You can watch for the spines and avoid them, but because of glochids, Opuntia cacti must be handled with tools, not with gloves.  The glochids will simply stick into the gloves and eventually get to the inside.  You would not want to wear gloves that have been used to handle prickly-pears any more than you would want to use a bedsheet that was used with fiberglass insulation.  The sheet may have worked for a while, but the hazard remains.  Just avoid getting glochids close to your skin as you would with fiberglass.  Both pose an unseen danger.  To get glochids out, you can use tweezers, tape, or soap and water.

                                                              A prickly-pear and its spines                         A glochid magnified hundreds of times

• Humidity and Temerature - A general rule of thumb is WARM + HUMID + NIGHTTIME + CACTUS = BLACK GOO.  I have read in numerous places that cold + wet will rot a cactus, but this is mostly hooey.  I have lost most of my cacti in the warm humid summer months, particularly when the nights have been warm and humid.  This is because of the biochemistry of cacti and other succulents, which is based on Crassulacean Acid Metabolism (CAM).  The big deal with CAM is that the plant saves water by taking up carbon dioxide at night instead of during the day, like most plants.  As a result of this, cacti need a difference of day/night temperature of at least 10 to 15 degrees Fahrenheit.  High humidity tends to prevent this difference, and this, combined with the humidity itself, probably weakens the plant and makes it vulnerable to attack by fungi and bacteria.  Fortunately, Opuntia cacti are almost immune to this.  However, if you have any non-Opuntia cacti in the ground, or even in pots, you may have noticed that one of them is a much darker color, or collapsed.  If you had noticed it earlier, you would have seen a black spot, usually near the base of the plant.  This can be scooped out throroughly, the plant rinsed and allowed to dry.  This will usually save the plant.  You need to stay vigilant during the hot, humid months, and it is very good to cover the plants with a sheet of Plexiglass when the weather is oppressively humid, and especially when it rains overnight.  Cacti of the genera Pediocactus and Sclerocactus are the most vulnerable, and are not recommended for the beginner.

References

Beginners

Michigan Outdoor Cactus Page (search by Google)

Heile, Kenneth D. 1993. Familiar Cacti (The Audubon Society Pocket Guides). An easy-to-find book, readily available online.

Spain, John. 1997. Growing winter hardy cacti in cold-wet climate conditions. A hard-to-find book.

Advanced

Benny's Cactus Page (search by Google)

Benson, Lyman. 1983. The Cacti of the United States and Canada. A rare and very expensive book with distribution maps which allow the advanced hardy cactus grower to identify hardy species and collections of species not generally considered hardy.  Look in your local public library.

Benson, Lyman. 1969. The Cacti of Arizona. Not as expensive as the first book, but contains mostly the same information, but limited to Arizona.  Readily available online.

Benson, Lyman. 1988. Native Cacti of California. Not as expensive as the first book, but contains mostly the same information, but limited to California.  Readily available online.