General Care for Cacti and Other Succulents
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The Basic Elements
The secret to success in growing succulents (or any plant for that matter) can essentially be reduced to a very few basic considerations - what I refer to as the "basic elements", which I summarize as:
Earth (potting Medium)
Wind (air, and air circulation)
Fire (light and temperature)
Water (watering, water quality, and fertilization)
Keep in mind that these are general guidelines only; there is no single formula which will work with all succulents - you may very well have to modify these guidelines for your own plants and circumstances. These are not formulas, this is not a strict regimen which must be followed precisely on a rigid timeline.
Long time growers understand that by varying one element, it may be useful to modify one or more of the other elements. For example - if you grow your plants at warmer temperatures, it may be necessary to water and fertilize more frequently, if there is good air circulation, it may also be useful to increase the frequency of watering. A different potting medium may require different watering schedules, and may require more or less fertilization. Feel free to experiment, learn what works best for you and the plants in your own collection, and realize that a few mistakes will not cause the immediate demise of your plant - this is perhaps one of the best traits of succulents - they are forgiving: forgetting to water the plant one or two weeks will probably have no appreciable effect on the plant - you couldn't say that about most house plants. The occasional overwatering will not have a negative effect on most healthy succulents - most species will tolerate a huge range of potting mediums - I have seen plenty of cases of growers who favored essentially soilless mixes comprised of peat moss and/or coir, perlite, and and other ingredients, some growers plant admit that they grow their plants in orginary garden compost and topsoil, or the mesa top dirt they dug during their trip to New Mexico, while others may produce a customized blend containing a multitude of ingredients which may include such exotic (and expensive) ingredients as fishbone charcoal, wormcastings, greensand and bat guanono; I have even know people who have grown their succulents hydroponically. The fact that these plants will grow at all when subjected to such a diverse combination of growing medium illustrates my point that these are generally very adaptible and forgiving plants.
For the most part, the advice which I offer here will give good results for the majority of succulent plants. There will of course be exceptions to my general guidelines - for example, a number of succulents are fall and winter growers - producing virtually all of their growth during the months when most other succulents are dormant. These plants include the Conophytums, some of the succulent Pelargoniums, and Gerianaceae. Unlike most other succulents, these winter growers will require increased water during the winter months, with reduced water in the summer (when these winter growers are dormant). There are other exceptions as well, but rest assured, the overwhelming majority of succulent plants which are most commonly encountered in the trade will respond well to these basic guidelines.
Perhaps the most important aspect in long term success in growing succulents is energy - both in the forms of light and temperature. For the most part, succulents are adapted to conditions of bright light, and generally warm conditions. Most species require bright light to thrive, so in the home, most succulents should be provided with the sunniest site available to produce their best growth. A sunny window, with a southern or western exposure is best, but an eastern exposure may be adequate for some species: very few of the succulents will thrive when given a northern exposure or a heavily shaded site. If the light levels are too low, it is possible to grow some species under artificial lights. I have grown a number of species (primarily Haworthias, Gasterias and a few miniature Aloes,) under fluorescent lights with good results. If plants are to be grown under fluorescent lights, the lights should be held only a few inches above the plants, otherwise the light which reaches them will be too dim to produce strong growth.
Where it is practical to do so, plants should be moved outdoors during the warmer times of the year (after any possibility of frost is past) to benefit from increased sunlight, warmer temperatures, and summer rainstorms. Light provides the energy for plants to grow - ultraviolet light, which is largely blocked by the glass in most types of windows, is important to produce strong growth, so the direct exposure to sunlight is especially beneficial to most succulents.
When moving plants outdoors, it is important to increase the exposure to daylight gradually: Just like people, plants need to protect themselves from the harmful rays from the sun, requiring time to produce their own version of a sun-screen, otherwise they can be permanently scarred by scorching. I first move my plants to a shady site for a few days, then to an area with dapple shade for a few days, then to a mostly sunny site for a few days, and then finally to a site which receives full sun for much of the day.
There are a number of succulents which are adapted to relatively shaded conditions, making these plants better suited as houseplants: Sansevierias ("Indian Hemp", "Snake Plant", and "Mother-in-Law's Tongue"), a few of the miniature Aloes, Haworthias, and Gasterias ("Bow Ties" and "Cow's Tongues") are typically more tolerant of lower light levels, but even these will produce their best growth when provided with relatively bright light.
Most (but not all) of the succulents grow during the summer months. When there is good light, adequate moisture and warmer temperatures, growth can be dramatic. Under ideal growing conditions, some succulents can easily double or even triple in size in a single growing season - a far cry from the popular belief that these plants are very slow growers.
It has been said that the most frequent cause of failure with succulents comes from watering plants too little during their growing season, and too often during the plantís resting season. When actively growing, most succulents will require substantial amounts of water: it is best to give them ample water (enough so that excess water flows through the drainage holes of the pot), watering the plants again only after the soil has become completely dry. Succulents should never be subjected to continually moist conditions, but during their growing season (usually in summer) it is just as important that the plants are not subjected to an extended drought. I typically water my plants once every 10 to 14 days in summer, but much less frequently in winter (when most of these plants are dormant) - about once every 3 to 4 weeks or so.
Most (but not all) of the succulents will also benefit when grown where they will receive summer rainfall. Rainfall can flush salts and harmful concentrations of minerals from the soil, which tend to accumulate when plants are exclusively watered with water from municipal water systems or wells. Summer rains can also assist in the control of certain harmful pests (spider mites for example), by washing them from the plants. Winter growing species (such as the Conophytums - one of the groups of plants commonly named "living pebbles") should be protected from summer rains, as too much rain during their period of dormancy may result in these plants dying from root rot.
Summer is also a good time to fertilize succulents. I generally choose a fertilizer which can be dissolved in water and applied when the plants are watered - fertilizers such as Miracle-Gro, Peters or Dyna Gro. It is also important to choose a fertilizer with a low concentration of Nitrogen. Fertilizers such as bloom boosters are a good choice: I also try to use a fertilizer which provides the trace elements - minerals which plants require in tiny doses. The trace elements include such things as copper, iron, zinc, boron and molybdenum (to name a few). I use Dyna Gro Bloom on my plants with good results. Succulents do not generally need much fertilization, so it is recommended to mix fertilizers from 1/3 to 1/4 the recommended strength (for example, if the instructions suggest mixing one tablespoon of fertilizer to a gallon of water, mix about one teaspoon to a gallon instead).
Water quality is another important consideration in growing succulents; well water and water from many municipal sources have significant levels of dissolved salts, and mineral compounds (calcium carbonate for example). In potted plants, these minerals will accumulate in the soil, and may eventually build up to levels which are detrimental to the health of plants (this accumulation of salts and minerals in the potting soil is probably the most important reason for periodically repotting plants). In recent years, there has been some discussion of the importance of watering succulents with acidified water. Not only does the use of acidified water limit the accumulation of these dissolved minerals, it is also important in the uptake of key nutrients from the soil. Ideally, the water used in watering succulents should have a Ph in the range of 5 to 5.5 - if a Ph test indicates that your water has a Ph above this, adjustments can be made by adding acid to the water until the water tests within the desired range. While I have not tried this on my own plants, using an acidifying fertilizer such as Miracid may be a good practice.
Succulents will occasionally require repotting. Most species may only need to be repotted every 2 years or so depending upon the species and the growth rates of the plants - faster growing plants may need to be repotted more frequently - slower growing species, and virtually all species of Conophytums and Lithops may go 3, 4 or more years before they should be repotted. In clustering plants, or plants with more or less spherical or hemispherical stems, repot in a pot which is about an inch wider than the plant (tall, cylindrical plants should be potted in low but wider pots to reduce the possibility of tipping). Always use a pot or planter which has drainage hole. Virtually all succulents appreciate a very gritty soil which provides excellent drainage, good penetration of air to the roots, and which is also reasonably fertile. Most commercial potting soils are not suitable for succulent plants: they are designed to retain moisture, and usually remain wet too long to keep succulents healthy. More often than not, blends which are sold for use with cacti and other succulents are not really good for these plants, at least in my experience: these contain too much sand, which is usually well draining, but contains virtually none of the nutrients necessary for healthy growth. I have found that soils which are blended for use with bonsai are also good for use with succulents - although I suspect that it may be best to blend in a bit of regular potting soil with this to provide a bit more water retention, as bonsai soil tends to have excessively sharp drainage.
I have had very good results growing Succulents in a potting medium containing a high percentage of Moo-Nure, a soil amendment comprised of composted forest debris and cow manure - while this may sound as though it is far too high in organic materials, I have found its ability to dry rapidly - even after it has been thoroughly saturated with water - to be especially valuable when growing succulents. It is widely available (in Central Ohio, it is carried by all Home Depots) and it is inexpensive.
Often forgotten as a requirement for plants, atmospheric gases, particularly oxygen and carbon dioxide, are nevertheless vital. Deprive a plant of these gasses, and it will quickly perish. Carbon, extracted from carbon dioxide during the process of photosynthesis is a basic building block of all living things, and is a necessary component of all proteins, fats and sugars.
Conditions of perpetually high humidity may impair the health of some cactus species. Humid conditions may provide environments suitable for the proliferation of molds, fungi, and bacteria as well as any number of insects pests. It is for this reason that I do not recommend growing succulents in a closed environment such as a closed terrarium - while some people can maintain succulents in a terrarium, more often than not, this is a formula for failure - if you are new to growing succulents - please resist the temptation of growing them in a terrarium - instead, consider growing them in an open dish garden.
Good air movement can be an important factor in the health of many succulents. Moving air may help to facilitate transpiration, and may help to limit the conditions of high humidity and may prevent the proliferation of certain pathogens. If you grow your plants next to a window, consider opening the window (weather permitting) to provide good air circulation. Registers and fans can also provide good air circulation, but remember that central heating and air conditioning will quickly dry out the soil, and plants grown near registers, fans, etc., will require more frequent watering.
Every bit as important, are the gasses which are present at the roots of a cactus. A soil which includes a high quantity of relatively large particles (coarse sand, gravel, stones, etc.) allows for the diffusion of air into the soil, and just as importantly, allows for carbon dioxide to diffuse out of the soil. Waterlogged soils do not allow for a free exchange of oxygen and carbon dioxide: in waterlogged soils, concentrations of carbon dioxide may rise to lethal levels, killing the roots. The same anaerobic conditions may create an environment suitable for the proliferation of certain soil fungi which will infect dead and dying tissues, and may ultimately kill the plant. This is usually what occurs when a plant is killed by "over-watering", the plant's roots essentially die of suffocation, and subsequently rot.
Most of the succulents should be given cool and dry conditions during the winter months, to keep these plants dormant. Dormant plants will usually tolerate temperatures which are quite cool, some to temperatures falling to the low 40's - but anywhere in the house which is a bit cooler than "room temperature"; window sills and Florida rooms for example, should provide adequately cool temperatures to keep the plants dormant. In winter, I water my plants very infrequently - about once every 3 to 5 weeks; other growers water their plants even less often than this, perhaps only one every 5 to 8 weeks, and a few will keep their plants completely dry through the winter months, and will only begin watering their plants in spring. Plants should be watered more frequently beginning in early spring - or when the plants break dormancy by producing new growth. Some species will show signs of new growth in response to the lengthening periods of daylight in spring, regardless of the frequency of watering. When plants spontaneously beak their dormancy, they should be watered more frequently, and periodic applications of fertilizer should also be made.
Most of the succulents are fairly disease and pest resistant, but a few pests are known to be a problem. Whiteflies, gnat-sized insects with whitish wings, which fly from plants in small clouds when infested plants are disturbed, are more typically a problem with other types of houseplants, and seldom infest succulents. On those rare occasions when they are present in succulent collections, whiteflies can be controlled with frequent mistings of warm water containing a few drops of liquid detergent. Insecticidal soaps such as Safers Insecticidal Soap may provide a greater degree of control, but may be slightly more hazardous when used in the home.
In greenhouses and other sites where plants are grown under hot and dry conditions, spider mites can become a problem. Spider mites are tiny - smaller than the period at the end of this sentence. In large numbers, spider mites are usually revealed by their communal webs which look tike tiny spider webs. If webs are present, look carefully for the mites, which (to the unaided eye) may resemble tiny brownish-red aphids. Small infestations can sometimes be dealt with by drenching the plant with water (a stream of water will often flush these pests from the plant): this process should be repeated every few days over about a two week period.
Mealy bugs and scale insects are pests which are difficult to eradicate once they have become a nuisance. Mealy bugs are slightly larger than the size of an aphid, and are typically of a grey to white coloration. Many individuals produce a waxy coating which may give them a whitish appearance, and some may produce such an abundance of fluffy wax that they look like tiny tufts of cotton. Mealy bugs usually occur in groups in the tight recesses of succulents, and are not always readily apparent - a few species live underground, and tap the roots of succulents, drinking the nutrient rich sap which flows in their tissues. It is therefore important to carefully inspect the roots of succulents whenever repotting. The most effective control of mealy bugs in small infestations is to seek them out and crush them - the more squeamish growers may prefer to dab these insects with a fine artists brush soaked in a solution of rubbing alcohol. There are some insecticides which may be effective against these pests, but - with the exception of Safers Soap, most of these products can be hazardous, and are not generally recommended for use in the home.
Scale insects may look like tiny grey or brownish blisters. I tend to think of scale as an insect take on the design of the limpet; the insect hides beneath a low conical "shell", and frankly, do not look much like an insect at all. Control of scale is similar to the control of mealy bugs, but because these pests may be a bit more cryptic than mealy bugs, they may be present in huge numbers before their presence is even detected. In all cases, large infestations of any of these pests may require stronger measures - use a pesticide designed for the control of the specific pest. Not all pesticides are suitable for use on succulents - some products may cause discoloration and scorching of plants, so it is generally recommended that a test be made either on a small (replaceable) plant, on a small portion of a larger plant. If no problems are evident after several days - it is probably safe to treat the entire plant. Always read and follow all instructions carefully - all pesticides are potentially hazardous, and all tend to be hazardous to a variety of other species, including beneficial insects, aquatic life, and birds and other wildlife. Treat all pesticides with respect.
As a rule, healthy plants which are actively growing tend to be fairly resistant to insect infestations, so the presence of insects may possibly indicate that the plants may be weakened due to some other cause: once the pests have been dealt with, a change in growing conditions may be indicated.
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