Growing Winter Hardy Cacti
In my opinion, there is nothing like the sight of a large and well designed cactus bed. Given a good sunny site, with proper soil preparation and plenty of space to grow, most of the hardy cacti will eventually achieve some pretty amazing proportions: these will also produce a more abundant display of flowers, and (if I can use the phrase with cactus plants) more lush growth than cacti which have been raised in containers. Even in the smallest cactus beds, there is usually enough space to grow a variety of plants, allowing the gardener to experiment with a number of species to discover on his or her own which plants fare the best in their climate, and to discover which plants they are particularly fond of. Even in the largest of containers, there is usually only enough space to grow a very few plants, allowing for less experimentation.
In central Ohio, any cactus in the garden is a novelty, and a larger planting including a wide selection of species and varieties of cacti is a rare sight indeed. My garden is a bit of a local landmark, and oftentimes, I find myself talking to distant neighbors who try to include a walk past my garden during their evening stroll, just to admire the plants. Cactus flowers are often quite large and showy, so when the cacti are in bloom in my garden, even people who are generally disinterested in plants and gardening will pause to admire the display. Cacti are icons of the American southwest, and even in the most unlikely situations, a cactus bed will conjure up impressions of grasslands, mountains, canyons and desert habitats. People who pause to admire the cactus bed often relate their tales of travels to "Cactus Country".
Creating a hardy cactus bed takes just a bit of planning, and a degree of physical labor; but like planting a tree, the worst of the work is finished when the bed has been planted; Thereafter, it is comparatively easy to maintain the beds. The gardener only needs to keep the bed free of weeds, make the occasional application of fertilizer, and do a few additional bits of periodic maintenance to keep the garden in prime condition. Once established, cacti will only require watering in the worst of summer droughts. The hardy cacti are virtually pest-
I try not to rely too much upon potent insecticides, as all insecticides may pose health risks to the gardener as well as to pets and wildlife, so any plants which are virtually immune to pests are especially valuable in the garden. Cacti do not require extensive fertilization. Fertilizers can be applied less often, and at much lower application rates than for most other garden plants, reducing labor, and saving money as well. Cacti are also quite easy to propagate, so it is often possible to give away or trade cuttings and seedlings with interested neighbors and other visitors.
Always locate the cactus bed where it will receive as much direct sunlight as possible. Anything you can do to increase the amount of light which is received by the bed will benefit the cacti. Tree limbs may be pruned to reduce shading of the bed; permanent structures (adjacent sheds, garages and fences) can be painted white to reflect additional light. While a number of species of cacti will tolerate varying degrees of partial shade, none of my hardy plants have suffered from too much sun during the growing season, and some species will require as much direct light as can be provided, so I cannot emphasize this point strongly enough.
Virtually all authorities recommend that the cactus bed be elevated above the existing ground to help assist in moving rainwater off of it, and to keep the soil a bit drier than the surrounding ground. The composition of this soil should be about:
1 part gravel
1 part coarse builder's sand
1 part good quality garden soil (with a bit of well rotted leaf compost if this is available)
The gravel which I use in my garden is pea gravel, but you may also use a mixture of pea gravel with larger sized gravel. I have used both the silica (quartz) type of pea gravel and river gravel which seems to be composed of weathered flint and various sedimentary rocks. I prefer the river gravel, as the quartz (silica) gravel is translucent, and may transmit light to the soil; for this reason silica gravel may be less effective in preventing the germination of some weed seeds.
I try to locate the coarsest grade of sand which I can find (do not use beach sand, as the particles are too fine, so rather than improving drainage and the circulation of air at the root zone, beach sand may actually impede the movement of air and water in the soil), If you can locate large quantities of fine granite chick grit, this may be substituted for the sand, but in my experience, this product is practically unknown in most urban areas, and even in more rural feed stores, is not always available.
If your garden soil is of a particularly good quality ( it should contain little or no clay) you may use this in your cactus mix, otherwise, it may be best to purchase a good quality top soil. If you have any compost produced from hardwood leaves (no lawn cuttings please) you may want to work this into your mix as well. I do use much of this in my mix -
One of the easiest types of raised beds to create is the simple mound. To build a mound, simply heap the cactus soil so that the center is piled to a height of about 12 inches or more and spread to a diameter of 3 feet or more.
The sloped sides of the mound will shed water, and the higher elevation will tend to keep the bed a bit drier than the surrounding ground. While this design may not quite provide dry enough conditions for the more moisture sensitive species, it is more than adequate for many of the hardy species, particularly the hardy Opuntias ("Prickly Pears") which tend to be comparatively moisture tolerant.
In a variation on a theme, I have seen very small raised beds made by filling an old tire with an appropriate cactus soil. The tire will shore up the soil, and is relatively small and easy to weed and maintain, but is only large enough for a small collection of the smaller species and varieties, or a taller growing cholla with a few additional smaller growing species. These tire beds are less attractive than raised beds built with more natural materials but these can provide a quick means to start a cactus bed; the exposed sides of the tire can be hidden by stones, brick or logs which may be added at any time after the bed has been created.
In making a raised bed, I will usually lay out the materials for the "retaining wall" first. This outlines the bed, and gives me some idea of the overall height and shape of the bed. I then dig out the soil which is inside this "perimeter" to the depth of my garden spade (approximately 10 inches). If the excavated soil is of a good quality; and is not too heavy, or does not contain too much clay, then I will use this to mix with my other ingredients to make the cactus soil, otherwise, it will be necessary to provide a good topsoil from another source. As I dig, I remove all weeds and extract as many roots, rocks and other debris as possible. When the soil has been completely excavated from the bed, I begin to fill it by alternately spreading bucketfuls of sand, gravel and soil, spreading each evenly into the bed. I recommend that each layer should be spread to a depth of no more than one or two inches. Once I have spread a layer of each material, I blend them together thoroughly with a hoe, garden rake or cultivator. I repeat these steps, periodically adding either a handful of bone meal or a small amount of a good bulb fertilizer as I go (applying these at about 1/4 of the recommended rate). When the soil nearly reaches its desired depth, I add the surface stones, filling in with additional soil to help to anchor them in the bed, so they will be less likely to shift over time. Remember to mound, or slope the top of the bed to facilitate the movement of rain off the bed. Beds which are completely level, or with depressions will tend to puddle, partially defeating the purpose of creating the raised bed in the first place. As a final step, I add about 2 inches of pea gravel to the top of the bed; this layer helps to suppress the germination of some types of weeds, and also provides some protection from soil being splashed onto the stems of cacti, preventing the spread of soil borne pathogens onto the stems of cacti. I have also seen larger river pebbles used as a top dressing in a cactus garden. This is an especially attractive material, and should be used more extensively where its cost is not prohibitive. In western states, decomposed granite is a popular top dressing for cactus beds. Some grades of crushed pumice may also be suitable, although in most regions of the country, pumice is prohibitively expensive. I have also seen photographs of cactus beds in New England, Long Island and the Chesapeake Bay area in which oyster shells were used as a top dressing for cactus beds. All work well, and each may offer certain advantages; the decomposing shells for example my provide some necessary nutrients to growing cactus plants and may be useful in maintaining those species which prefer lime in their soil (Opuntia arenaria, and many species of Sclerocactus for example). Usually the choice is based upon economics and appearance; if the material provides very quick drainage, and you like the look, the price is right, and if it is available in virtually unlimited quantities, it should be suitable for your needs.
Mounded beds can be created in any shape or size desired, I find that it is best to create relatively narrow beds so that no portion of the bed lies beyond the reach of the gardener, otherwise, portions of the bed will eventually support an intractable population of weeds. If a bed is to be very large, remember to include paths through it to provide access to all portions for periodic maintenance.
It is best to plant the beds in spring or very early summer, either just before the cacti have broken dormancy, or just afterwards. I usually plant my beds with young seedlings and small rooted cuttings, so the newly planted bed may look nearly vacant upon completion. But growth can be quite rapid, and by the next year, many of the plants have grown significantly, some of them achieving blooming size.
While the species of Opuntia ("Prickly Pears"), Cylindropuntia ("Cholla"), and Grusonia ("Club Chollas") are reasonably forgiving about planting depth, and will probably grow if they are placed on the surface of the ground, or if they are half buried or anywhere in between. I usually choose to plant these just deeply enough so that the soil and gravel will hold the stems in place without toppling. Other species are not so tolerant; in transplanting the more columnar and ball shaped genera (Escobaria, Echinocereus, Pediocactus, etc.), care should be taken to assure that the plants are not buried too deeply in the soil, as this may induce rotting in the stem. Ideally, these plants should be planted at exactly the same depth as they had been growing prior to being transplanted. The area where the roots emerge from the stem (The crown) should rest on the surface, be just barely covered with soil. As a precaution against planting some plants too deeply, I will only partially cover the roots with soil, and will fill the remaining depth with gravel to a height where it will just support the stems. This keep the stems out of direct contact with the soil mix, and may help prevent the stem from rotting.
Hardy Cacti in Planters
Not everyone can devote much space to growing cacti: perhaps you live in an apartment or condominium and cannot plant a garden, but you could grow a small collection of plants in a planter or tub. There are a number of cacti which are suitable for planters, the smallest species of Opuntia for example, and the hardy species of Echinocereus (the hedgehog cacti), and Escobaria are also good candidates for growing in containers.
There are several advantages to growing in a container: It is possible to keep the soil a bit drier; not only will moisture drain from the bottom of the pot, but will also evaporate through the pot surface itself (in unglazed porous containers). If the planter is not in direct contact with the soil, ground moisture will not be continually drawn to the surface. A planter will raise smaller plants to a height where they can be more easily seen and appreciated. The container may either be moved or covered during the cold and wet months so that the cacti can be sheltered during the worst winter weather, making it possible to grow some of the more moisture sensitive cactus species.
Some of the disadvantages to growing cacti in containers include the following: Many cacti will not grow their best when their roots are confined; they tend to grow smaller, produce fewer blooms, and lack some of the vigor of cacti grown in open beds. Containers transmit heat, and may subject the roots of cacti to unusually high temperatures in the summer and lower temperatures in the winter than the roots of cacti which have been planted directly in the ground, subjecting these plants to additional stresses during extreme weather conditions. Plants grown in containers are essentially at the mercy of the grower, who must assure that the plants receive adequate daylight, moisture, fertilization and protection from extremes in temperature. While most species will tolerate a certain degree of neglect, most will eventually languish and die when completely neglected in a container.
In making a container planting of hardy cacti, the most important considerations are: setting the container where the plants receive as much direct daylight a possible, while simultaneously keeping the sides of the container somewhat shaded from direct sunlight; and a potting medium which is sufficiently porous and fertile. If you can provide these, you should be able to successfully grow quite a number of attractive species.
The potting medium for container grown plants is much the same as the soil recommended for plants grown in an open bed: One part good garden loam (do not use commercial potting soils, as many of these contain high percentages of peat and/or peat moss, both of which I have found to be unsuitable for growing hardy cacti). This is the portion of the soil from which your cacti will derive most of their nutrition, so this may be the most important component of your potting mix. Avoid clay laden soils, and try not to use top soil which contains a high percentage of manure or other organic materials. To this add one part very coarse sand. Do not use white play sand or beach sand, the particles of these grades of sand are much too fine, and rather than increasing the porosity of the soil, these smaller grains tend to impede the passage of water and air through the soil. The larger the sand particles are, the better suited they will be for the cacti; if in doubt, it may be best to substitute fine aquarium gravel for the sand. Recently, I have been experimenting with fullers earth, an kiln fired clay product which is similar in appearance to clay cat litter. Some products made from this material are made specifically produced as a soil amendment for baseball diamonds, putting greens and to improve the porosity of soil for lawns and gardens. I have used one such product which is sold locally under the name of "Turface All Sport". The particle sizes of this products is ideal, increasing the porosity of the soil; it is absorbent, absorbing excess moisture and releasing moisture gradually as it is needed, thus moderating excesses of flood and drought; unlike cat litter (which it resembles), fullers earth is stable and will not revert back to clay when it becomes saturated with water. If you choose to use fullers earth, use this instead of the sand, as it more suitable for growing cacti than sand. And finally, I mix in one part pea gravel. I try to avoid using crushed stone, as I believe that the sharp edges on these may injure cactus roots.
If the planter is located in a particularly sunny and dry area, it may be best to increase the percentage of topsoil in the mix so that the mix retains moisture a bit longer. If the location of the container is in an area which is somewhat shaded part of the day, or if you are growing cacti which are particularly sensitive to excess moisture, then it would be a good idea to increase the proportions of sand (or fuller's earth) and gravel in the medium to provide additional drainage for your plants.
In choosing a container, it is vital for it to have drainage holes in the bottom. If there are no holes present, it may be possible to drill them with an electric drill, but I would recommend that you do not purchase any planter which lacks drainage holes; it is time that the manufactures of decorative pots and planters realize this is a necessary attribute for any pot intended for plants.
I have had the greatest success with containers with thick walls, such as hypertuffa planters, cement planters, chimney liners and concrete pipes stood on end. It is my belief that thicker walled containers may provide a greater degree of insulation, and will not transmit heat as rapidly as thinner walled containers. Thicker containers may also store heat during the day, slowly dissipating the heat during the night, cooling the roots gradually and gradually warming them by day. "Whiskey barrels" are probably also very good, as these also have thick walls, but I have not used these with cacti, and cannot report on how well cacti will grow in these.
All of the hardy cacti which I have grown seem to prefer growing with their roots unrestricted, so it is best to provide a container which is as large as possible: very large terra cotta pots, planters, halved "whiskey" barrels, hypertuffa planters, stone troughs and ceramic chimney liners are all suitable for hardy cacti. As a rule, smaller pots are too small for most species of hardy cacti, which will quickly exhaust all the nutrients contained in the soil, and will require frequent applications of fertilizer, or periodic repotting to keep the plant healthy.
Fertilizers and Fertilization
Cacti are generally very frugal feeders, requiring little fertilization: in habitat, many individuals may survive for decades on very lean soils. But because our severe winter weather, our higher rainfall, and humid summers test the tolerance of many species, it is beneficial to give your plants an occasional boost with periodic applications of fertilizer.
I recommend the use of a fertilizer which contains comparatively low concentrations of nitrogen. Nitrogen promotes rapid growth, but such rapid growth in cacti produces plants which look unnatural, and results in growth which is weak, flabby and vulnerable to frost damage during the winter months. I prefer to use a high quality fertilizer which is formulated for use with bulbs; such fertilizers have proportions of nitrogen, potassium and phosphorous which are well suited to growing cacti. Other growers prefer to use a fertilizer which is balanced for use with tomatoes and other vegetables. Both bulb and vegetable fertilizers are readily available, and are generally not too expensive. In choosing a fertilizer, I generally look for one which releases its nutrients slowly over the course of the growing season, and which also includes a good balance of the trace elements. The trace elements are comparable to vitamins, they are necessary for the health of plants, but are required in minute doses. Never use a fertilizer balanced for use on lawns, these contain concentrations of nitrogen which are far too high for cacti, and many lawn fertilizers may contain herbicides which will kill cacti.
I recommend three applications of fertilizer each year. The first application should be made in spring, just as the plants are beginning to show signs of growth. This application should be at about one third of the recommended application rate. The second application should be made in late spring or early summer, just as the cacti are finishing their blooming season and beginning to fruit. Use about one fourth the recommended application rate. The third application is optional, and may be made in August to help strengthen the stems and roots. Use only minute quantities of fertilizer at this time, otherwise the plant may begin a renewed growth cycle, which would leave the plant vulnerable to frost damage and subsequent rot. One grower suggests that a very light application of super phosphate should be made at this time. During extremely cold weather, a number of cacti will develop a pronounced reddish or purplish color in their stems. This is because some species cannot properly metabolize phosphorous during cold weather, causing stems to become more reddish. This symptom is only temporary; when the weather warms again in spring, stems revert back to their usual color. While this temporary deficiency does not appear to cause any significant distress to the plant, the application of a bit of phosphorus just prior to the outset of cooler weather may help strengthen stems and roots, and may and may also help plants survive harsh winter conditions.
Some authorities would advise against this last application, but I believe that when applied in minute doses, a little fertilization may help a plant to store the nutrients it may need for renewed growth the following spring; so I leave it to your judgment. In any case, always remember that it is better to under fertilize than to over fertilize; when in doubt, use less.
Some authorities may recommend the application of bone meal and periodic applications of well rotted compost instead of using chemical fertilizers. This is a good practice, but remember that bone meal must be broken down by soil bacteria before its nutrients can be absorbed by plants. Given the unusually porous nature of the recommended soil mix, it is possible that much of the bone meal (and its phosphorus) will have been leached from the soil before it has broken down sufficiently. If you make applications of compost to your cactus bed, be certain that this contains only a small proportion of lawn cuttings, as compost from grasses will contain a greater percentage of nitrogen. Do not use animal manures unless these have been thoroughly composted, preferably for at least two years. Fresh manure is too rich in some nutrients, and may also contain an abundance of viable weed seeds which will subsequently choke your garden. Do not use dog and cat manures, as these may harbor pathogens which can be transmitted to people.
The Prickly Pears (Opuntia), and their close relatives the Chollas (Cylindropuntia), and Club Chollas (Grusonia), are amongst the easiest and most adaptable of of the hardy cacti, and while I have featured a few of these species on my Winter Hardy Cactus Garden page, a much more comprehensive treatment of these plants can be found at The Opuntioids of the United States, a site created by Joe Shaw and David Ferguson, featuring descriptions and numerous photographs of many species of the Opuntias and their relatives in the United States. While many of these species are not hardy plants when grown in Ohio, there are a good number of species which will prove to be hardy here. Habitat information is a good indicator of the cold hardiness of many species. Plants which are native to the Texas panhandle, Oklahoma, northern New Mexico, Colorado, and much of Utah for example, are generally good contenders for Ohio gardens, also plants which grow in alpine regions. Their site is an excellent resource, and should be checked to give you habitat information and a better impression of the general appearance of each "opuntioid" species.