- Waterwise Gardening | David Salman
Gardening with Cold Hardy Cacti
Cacti are some our most spectacular native flowering plants, but often our most overlooked wildflowers when planning and planting a xeriscape. Cacti not only contribute stunning flowers in spring and summer, but also provide year-round interest with their structural evergreen stems and geometrically arranged spines.
Native only to the Americas, cacti represent a diverse group of perennials that have adapted to a wide range of habitats. There are a number of species that grow in USDA zone 7 and colder areas. These cold-hardy beauties can be successfully mixed into landscape plantings when their cultural needs are understood and provided for.
The keys to successful cultivation of cacti include:
proper soil preparation,
correct placement in the landscape
planting them with suitable companion plants
Cacti require a fast draining soil. This means no clay and no added compost, peat moss or other soil conditioners which make the soil too rich in nitrogen and humus. I recommend only Planters II trace mineral fertilizer and Yum Yum Mix be used. I also recommend a berm created with a mix of small gravel, coarse sand and very little soil.
Most cacti prefer full sun and benefit from warm protected microclimates where rocks, buildings or pavement absorb and hold heat.
Cacti benefit when grown with other plants as long as they’re not smothered by large and fast growing companions. In wetter climates companion plants also help pull moisture from the soil and keep cacti drier. Clump grasses are particularly helpful in this way.
In the wild cacti are rarely if ever found growing only with other cacti. Unfortunately many cacti are relegated to cactus-only plantings. This “pincushion” look deprives the gardener of the opportunity to combine them in artful ways with non-cacti plant and thus extend the blooming season.
A number of cacti are native to the Great Plains. Whether found growing directly in the grasslands or in rock outcroppings, these species are the most moisture tolerant, cold hardiest and easily grown of the barrel-type varieties and include:
Echinocereus reichenbachii and reichenbachii subspecies albispinus, caespitosus and baileyi,
Escobaria vivipara (formally classified in the genus Coryphantha) and Escobaria missouriensis.
Among recommended companion plants for these prairie species include:
Flame Flower) (Talinum)
Perky Sue (Hymenoxys)
Indian Paint Brush (Castilleja integra)
Prairie Gayfeather (Liatris punctata)
Sulfur Buckwheat (Eriogonum)
Butterfly Weed (Asclepias tuberose)
Blue Mist Beardtongue (Penstemon virens)
Prairie Zinnia (Zinnia grandiflora)
Blue grama grass (Bouteloua gracilis)
Prairie Dropseed (Sporobolus heterolepis)
Other ornamental species are native to high, dry cold areas of the southwestern United States and northern Mexico. They aren’t quite as cold-hardy and are bothered by extreme temperature swings in the spring and fall. They also like hotter, drier conditions, especially during the winter months. This group includes: Echinocereus fendleri, Escobaria orcuttii v. koenigi and Ferocactus wislizenii.
For companion perennials with these, try the following:
White Bush Zinnia (Zinnia acerosa)
Furman’s Red Bush Sage (Salvia greggii)
Giant flowered Purple Sage (Salvia pachyphylla)
Pineleaf Beardtongue (Penstemon pinifolius)
‘Margarita BOP’ Beardtongue (Penstemon x heterophyllus)
Silky threadgrass (Nassella tenuissima)
‘Nezpar’ Indian Rice Grass (Oryzopsis hymenoides)
Big Sage (Artemisia tridentate).
My favorite species from the intermountain West can be planted with either of the above groups. Echinocereus triglochidiatus (Claretcup) with its late spring display of orange flowers is our largest and showiest cold-hardy clumper. ‘White Sands Strain’ is the biggest and most vigorous growing member of the species and matures to a massive (2-3’ tall x 18-24” wide) cluster of 5” diameter stems. It can be used as the centerpiece for any xeric planting. I like to combine it with Sotol (Dasylirion wheeleri), the rare Yellow Texas Yucca (Hesperaloe parviflora “Yellow”) and Beargrass (Nolina microcarpa).
Maintenance is the final component to a healthy cactus planting. Always keep cacti mulched with gravel. I prefer crushed (angular) gravel to a depth of 2”. Remember to replenish gravel mulch annually; freezing winter weather causes the soil to contract and expand pulling the gravel down into the soil and thinning the layer above ground.
Established plants grow fastest when watered regularly, once every 7 to 10 days during the heat of the summer (when there is no rain). Stop watering by early September to let the plants dry down and shrivel in preparation for winter. Fertilize no more than once a year. I like to top-dress with Yum Yum Mix at the start of summer.
Trim companion plants during the growing season as needed if they overgrow their cactus neighbors. Remove all fallen leaves from around the cacti and cut back any plants that create winter shade. In wetter climates that get a lot of winter/early spring rain, it is helpful to create an open-ended tunnel with plastic sheeting and bamboo hoops to keep the bed dry. Remove in mid-spring as the plants begin to wake up and grow. Summer is an ideal time to transplant heat-loving cacti and desert plants and grasses.
For more information, refer to these books about cacti:
Growing Winter Hardy Cacti
Cacti: The Illustrated Dictionary
Growing Classic Cacti
We think of cacti in small pots or dish gardens for use as house plants, but cold hardy members of this diverse family have the potential for much broader use.
As often happens with native plants, we tend to overlook them when we plant our gardens and landscapes. This certainly is the case with the group of succulent plants known as cacti. Mostly we think of cacti as grocery store items grown in small pots or dish gardens for use as house plants. However, the cold hardy members of this large and diverse plant family have the potential for much broader use. They are very showy in outdoor plantings where their spectacular flowers, fascinating spination and bold evergreen stems add interest and diversity to our plantings.
Cold-hardy Cacti in their Native Habitat
Cacti are found as native plants only in the Western hemisphere. Occurring throughout North and South America, the greatest concentration of species is found in Mexico northward into Arizona, New Mexico and West Texas. Although we think of cacti as being strictly low desert plants many species are found in some very cold, harsh environments. As more and more gardeners experiment with the various cold-hardy species, we can look to plant them more widely and expand their usefulness as garden plants into a much larger portion of the United States.
The habitats of most cold-hardy cacti are concentrated in the mountains of northern Mexico and the western United States. Additional cold-hardy species are also found in the mountains of southern-most Argentina and Patagonia. In the United States, several genera are native to the western Great Plains ranging from Oklahoma northward into Montana and the Dakotas. One species of Escobaria can even be found venturing into the southern edge of central Canada! The vast intermountain region is also home to numerous species. Many are found in both the mountains and the high, cold desert plateaus of this area.
The Chihuahuan desert in West Texas and southern New Mexico is also home to a treasure-trove of fascinating cold-hardy cacti. It is interesting that the cold hardiness of many species from West Texas and the Southwest exceed what we would expect given the historic lows recorded in this century. It seems that many of them retain their genetic cold hardiness from many thousands of years ago when those regions were much colder.
There are over 100 genera of cacti. But the majority of cold-hardy species are concentrated in a dozen or so. For the purposes of this article I have defined “cold-hardy” as cold tolerance to temperatures of 0°F or lower. The most cold-hardy include Great Plains natives like Escobaria, the wide ranging Opuntia and mountain dwellers such as Echinocereus and Pediocactus which can withstand winters lows of -30°F and colder.
Garden worthy Species
The largest genus of cold-hardy cacti is Echinocereus, commonly known to as hedgehog cacti. Important ornamental species in the genus include E. triglochidiatus, E. viridiflorus, E. reichenbachii, and E. fendleri. However, there are many other species in the genus that have cold-hardy members as well. This is one of my favorite genera because of the vast numbers of subspecies and variants that can be found. In fact, there are many collectors who concentrate solely on this huge group.
The orange flowered species Echinocereus triglochidiatus (USDA zones 5-10) includes a huge number of subspecies and geographic variants. They range in form from huge 3 foot wide clumps with hundreds of spiny stems to small, nearly spineless types found in the mountains of central NM and the plateaus of western CO.
Another of the hedgehogs that is an accommodating garden dweller is Echinocereus reichenbachii (USDA zones 5-10). The showiest forms are clump forming and are found in the rocky hills of south central and western Oklahoma. The tight, attractive, comb-like spines are among the most gardener friendly of the cactus family and vary in color from pure white to pinkish-brown. The masses of pink to magenta flowers are extremely showy. Echinocereus reichenbachii is a fast grower (for a cactus) and blooms at an early age. It is also a ready re-seeder if it likes its spot in the garden.
Echinocereus viridiflorus (Green flowered Hedgehog) is another wide ranging species native to the short grass prairies and foothills of northeastern New Mexico north through Colorado, Oklahoma, Kansas, Nebraska into Wyoming. The yellow-green to green flowers are unique and sometimes lightly fragrant. The spines of plants for selected localities can have very colorful bright red and white spines that contract beautifully with the green flowers. This species is very cold hardy (USDA zones 4-9), easy to grow and is a good choice for higher rainfall areas. Echinocereus fendleri(Fendler’s Hedgehog) is another favorite of mine with its enormous magenta flowers in late spring. The spination of this plant can be quite showy as well. Fendler’s Hedgehog is extremely heat tolerant, but it demands excellent drainage and should be protected from excessive winter moisture.
Two other large genera that are very closely related taxonomically are Escobaria and Coryphantha. Here we find another fascinating array of species. Escobaria vivipara (USDA zones 4-9) is the widest ranging of all the species. This clustering species is long blooming and adapts readily to cultivation. It is a good starter species if one doesn’t have much experience gardening with cacti.
Because of this species wide range, we also have a huge number of interesting subspecies to add to our gardening pallet. Some of my favorites include the magenta flower species E. vivipara, E. vivipara v. rosea from the mountains of Nevada with its huge purple flower and the small stemmed E. vivipara v. bisbeeana from southeastern AZ with its tight white spines and pale pink flowers.
Another extremely cold-hardy species, Escobaria missouriensis (USDA zones 4-9) originates from the western Great Plains. This species is typically clustering with a profusion of greenish-yellow flowers in late spring. It too is readily adaptable to garden culture and mixes well with other non-succulent prairie wildflowers.
Of the genus Coryphantha, one of my favorites would have to be the little known species from West Texas, Coryphantha echinus (USDA zones 6-10). It is proving to be a durable and reliably cold hardy gem. The white, very symmetrical spination makes a fine backdrop to the glowing yellow and orange centered flowers. C. echinusblooms for a long period in the heat of early summer.
Another fascinating species sharing the same range as Coryphantha echinus is Echinocactus texensis (USDA zones 5-10) commonly known in Texas as Horse Crippler. Unfortunately because of its stout spines it can puncture a hoof, ranchers relentless rouge this species from pasture land so their livestock won’t step on them. However, as a garden specimen this barrel type species is much more valued. It can grow to a foot or more in diameter. The thick claw-like spines are very ornamental as are the large burnt orange flowers that ring the top of the flat stem. Later in the summer the large showy orange fruit crown the plant.
Ferocactus hamatacanthus (USDA zones 6-10) is the most cold hardy of the Ferocactus genus best known for its whopper sized specimens found in the Sonoran and Mojave deserts. Ferocactus hamatacanthus however is from West Texas and is considerably smaller, growing to 15 inches in height and a foot or more in diameter. It has long (often 3 to 4 inches) hooked pink or straw yellow spines and large showy yellow flowers.
The Pediocactus are a small genus of cacti with Pediocactus simpsonii (USDA zones 4-7) and its subspecies v. minor being the most widespread. It is a sub-alpine species most often found in the higher altitudes of the many mountain ranges in New Mexico, Colorado, Utah, Nevada, and southern Idaho. As one might expect Pediocactus simpsonii is happiest in gardens located above 5,000 ft. in elevation. This species which varies in size from tiny single plants to large clusters of tall stems, doesn’t mind partial shade especially at lower altitudes. Be aware that it detests humid heat. However, when happily situated in the garden the pink, white and sometimes yellow flowers are a welcome sight in early spring. (Note that the flower color is variable for this species through its range.) Pediocactus simpsonii often blooms while there is still snow on the ground.
Though the genus Opuntia includes some very difficult to handle species, I do recommend using Opuntia basilaris (USDA zones 5-10) or Beavertail cactus from the Mohave desert. The naked pads are ornamental in their own right, but the double flowered pink or yellow flowers are breathtaking. Place it where it will receive baking heat for best growth and flowering. Give this species some room to spread, as it can grow to cover a 2’ by 2’ wide area. Don’t hesitate to prune it back should it start to overgrow the smaller plants around it.
Reprinted from the March/April issue of The American Gardener with permission of the American Horticulture Society. 7931 E Blvd Dr., Alexandria, VA 22308 or on the web at www.ahs.org.
How to Grow Cold-Hardy Cacti in the Garden
In the garden cold hardy cacti are not difficult to grow if you keep their basic requirements in mind. First and foremost, cacti require excellent drainage. Secondly, they like alkaline, mineral soils. That is, they need lean soils that have not been amended with lots of sphagnum peat moss or compost. And thirdly, they should be situated to receive full sun, especially during the winter months.
Drainage is critical to the health of a cactus plant’s root system. Planting cacti into water retentive soils like heavy clays and rich loams will result in root rot. Low spots that collect water should also be avoided. Excellent drainage is particularly important during the winter, especially in areas that receive frequent rains or snows. I recommend planting in raised or bermed (mounded) beds, especially where the native soils hold water and stay wet.
To create a lean, fast draining soil for these raised beds and berms, mix the native soil with one half coarse sand by volume. Add to this mix the minerals that cacti crave by incorporating Planters II (a natural trace mineral fertilizer) and phosphate at recommended rates. Working larger rocks into the planting area also adds a pleasing landscape element. Well-placed rocks also create pockets of soil that duplicate spots where cacti are found growing in the wild.
Situating the planting area properly is also of critical importance. Locate planting beds in full sun against south and west facing walls, or in hot, dry areas surrounded by cement sidewalks and driveways. When looking for a planting spot, be sure that a garden bed in full summer sun doesn’t find itself in the shade as the sun drops lower in the winter sky.
Transplanting Techniques for Cacti
When it comes time to plant your new cacti, several techniques can be used to improve transplanting success. Most importantly, always plant cacti bare-root. Wait for the soil in the pot to dry out. Then gently loosen the soil in the root ball with your fingers and shake it off. Once the soil is gone trim the roots back by 1/3rd with sharp scissors or pruning shears. Plant into a shallow hole, spreading the roots out evenly. Back fill the hole holding the cactus so the crown (junction of root and stem) in just above the surrounding soil. Settle the soil between the roots by carefully vibrating the plant up and down. Now mulch with crushed (not round) gravel to a depth of 1 to 2 inches depending on the size of the plant. Don’t worry when the gravel covers some of the spines up from the base of the plant. The mulch will settle a bit with time.
I wait a day or two to water in the new transplants. This gives the cut roots time to callus over. At that point I water thoroughly with a root stimulating mixture of seaweed and a dilute high phosphorous fertilizer. When watering cacti, it is better to err on the side of dryness than to overwater, especially in the colder months. However, during the heat of the summer cacti will respond positively to a weekly soaking.
Maintenance Tips for Healthy Cacti
A well designed planting of cacti and companion plants should make for a low maintenance garden. Apply a single application of a granular fertilizer in late fall or spring. I prefer organic formulations especially those with alfalfa meal. This should be supplemented with a dose of liquid seaweed several times through the summer. With the arrival of fall, watering should be discontinued to allow the cacti to shrivel and harden off for winter.
Fall clean-up is also important. Remove fallen leaves and prune back the stems of neighboring plants that have grown over or around the cacti. This helps to keep the cacti dry during the winter by facilitating maximum sunlight and air circulation around the plants.
Incorporating Cacti into Landscape Designs
Here in Santa Fe and throughout the western US, water-wise (Xeric) garden designsare becoming increasingly popular. Xeriscaping not only promotes water conservation, but emphasizes the importance of using plants that are well suited to our rugged, arid climates. Indeed, cacti are ideal xeric plants and will greatly enhance any landscape planting by adding colorful flowers and a year-round structural element with their handsome evergreen stems.
The key to creating a satisfying garden design that includes cacti, is an understanding of how they can be used in combination with other plants. In habitat, cacti are found growing among a variety of succulent and non-succulent plants. It is important to dispel the misconception among some gardeners that cacti can only be planted with other cacti. This type of design fails to take advantage of the beautiful plant combinations made possible by combining non-succulents with the cold hardy cacti. It also avoids the negative result that I have heard termed a “pincushion garden”.
There are several design philosophies that can be used as guidelines for creating a good looking garden that includes cacti. From the standpoint of native plant use, I recommend making a plant list based on species found in a given region of the western US. This approach will make a replica of the landscape you might encounter if you were hiking in the Colorado foothills or along a mountain path in the Chihuahuan desert. Done in an aesthetically pleasing manner, this type of garden can be beautiful, educational and attractive to hummingbirds and other creatures that recognize home.
The other approach that I often suggest is to make a plant list that includes a variety of compatible cold hardy xeric plants without regard to the plant’s status as native or non-native. For example, the plant list would include succulent South African groundcovers from the genus Ruschia, some Lavender cultivars and other interesting rock garden sized plants from the Mediterranean region of Europe. Additional plants would include some US natives like Agave and Agastache. This more cosmopolitan design is also recommended for areas outside of the western US with climates that would be mis-matched to the preferences of xeric western native species.
Recommended Companion Plants
A short list of favorite US natives that I like to use in my cacti xeriscapes include herbaceous perennials such as:
Perky Sue (Hymenoxys species)
Skullcap (Scutellaria resinosa and S. suffrutescens)
Sundrops (Calylophus species)
Pineleaf Beardtonque (Penstemon pinifolius) and other small growing Penstemon species
Cold hardy Salvia greggii cultivars like ‘Furman’s Red’
Hummingbird Mints: Agastache species, and Flame Flower (Talinum calycinum).
Evergreen succulents include:
Agave parryi and A. utahensis
Sotol (Dasylirion wheeleri)
Texas Red Yucca (Hesperaloe parviflora).
Woody shrubs like Big Sage (Artemisia tridentata) and “Apache Plume”http://www.highcountrygardens.com/catalog/product/51450/ (Falugia) blend nicely, particularly with the larger growing cacti.
The cold hardy Mediterraneans offer many wonderful companion plants. Among my favorites are the English Lavender (Lavandula) cultivars as they are culturally very compatible with the cacti. As a group, the other hardy ornamental herbs are also excellent.
Other favorites include the miniature groundcover Speedwells (Veronica thymoides and V. oltensis).
Other mounding rock garden perennials like Greek Yarrow (Achillea argentea), the succulent Hen and Chicks (Sempervivum cultivars), Persian Rockcress (Aethionema species), Basket-of-Gold (Alyssum species and Mt. Atlas Daisy (Anacyclus depressus) fit in nicely as well.
When using either design approach, be sure to choose plants that are not too large. Avoid pairing a large, fast growing plant with a smaller, slower growing cacti. After a year or two, the more vigorous plant may smother the cactus and kill it.
Protecting Cacti in the Wild
An important part of installing a garden is purchasing the plants. It has been an unfortunate fact that many gardeners with their infatuation with cacti have purchased plants collected from the wild. Over time, this has decimated the populations of many cactus species in their native habitats. It is of utmost importance to purchase plants form reputable nurseries that propagate the cacti they sell and do not re-sell wild collected plants. Nursery propagated plants will transplant readily with few loses. On the other hand most wild collected cacti struggle and die when removed from their homes.
Another advantage of buying nursery-propagated plants is that quite often the plants come with information concerning their origins. This collection data (where the original seed was found) adds a lot to the horticultural value of that plant. Many species have tremendous variability throughout their range. These differences include variations in stem size, spination, and even flower color. This is of particular interest to gardeners who enjoy building a collection of the various cactus species. Collection data also gives valuable information regarding cold hardiness. Many species exhibit increased cold hardiness within their range, particularly when it is found in more northerly, high elevation locations.
Designing gardens to include the use of cold hardy cacti opens the door to a new way of thinking about this family of stunning native plants. Excitement about discovering them will no doubt have you walking you landscape, looking for a suitable spot to plant a grouping of cacti and some companion plants.