Plants of the genus Ariocarpus are successfully cultivated in many countries of the World and consequently under a very wide range of climatic conditions. It is therefore impossible to give prescriptive cultivation information except for physical tasks, e.g. grafting techniques. What is possible, however, is to give general guidelines for the reader to adapt to their local conditions. The information given here has a natural bias to the climate in Britain and Northern Europe. Contributions from growers with other climatic types are sought so that inexperienced growers may select a best-fit starting technique.
Cultivation information falls into two main broad categories, seed raising and other propagation techniques, and growing post-seedling and mature plants A third category is the avoidance and control of pests and diseases, although much of this information is given in the other two sections where appropriate. Because most people will naturally first want to successfully grow plants already in their possession before moving on to propagate plants this is the first topic to be dealt with.
Cultivation of Mature Plants
The essential ingredients for the successful growth of these plants are very similar to those required for other cacti and succulents. Although they do have a few special needs, contrary to popular belief, they are not difficult to grow and flower well in climates very different to their homelands. As usual, it is just a matter of the right combination of soil, potting, watering, feeding, light, temperature and ventilation conditions, all of which are heavily interdependent.
Soil and Potting
In the wild all Ariocarpus, without exception, grow in a calcareous soil of some type, seemingly from choice. In most cases the calcareous material is limestone (calcium carbonate) although many populations of A. kotschoubeyanus grow on gypsum (calcium sulfate) mud silt flats, but some also on limestone. Limestone fragments are generally admixed with a hard sandy-clay, high mineral, low humus containing soil in pockets between larger limestone rocks or pavement. The most successful populations occur where the limestone is porous and friable, e.g. the excellent and plentiful specimens of A. fissuratus reported from the Boquillas limestone region of the Big Bend, Texas.
The above strongly suggests that soluble calcium, together with other minerals, is an essential part of the diet for Ariocarpus, and this has been verified in cultivation. Calcium sulfate (gypsum) is slightly water soluble and ground water, rainwater or dews release free calcium ions. In contrast, limestone is almost totally insoluble in water and calcium release occurs by the chemical dissolution of limestone by water and carbon dioxide from the atmosphere (carbonic acid) to produce calcium bicarbonate which is water soluble and available to the plant. This calcium dissolution mechanism to form calcium bicarbonate and its subsequent decomposition back to insoluble calcium carbonate is how stalactites and stalagmites have formed in limestone caves over many thousands of years. This dissolution mechanism is also the cause of temporary hardness in water from limestone regions. Solubilisation of limestone by this route will be accelerated where the limestone is friable, more porous or more finely divided and this is the most probable explanation why the best and most successful populations occur at these locations. Contrary to a common misconception, limestone soils are not highly alkaline - limestone itself is virtually insoluble in water and the amount of calcium bicarbonate, which has only a very mildly alkaline reaction, produced at any one time is tiny and transient as it is quickly consumed by neutralizing acidic constituents in the soil (humic acids etc.), facilitating the release of essential minerals from complex clay structures and by the plant itself. Limestone soils are, therefore generally slightly on the acid side of neutral to slightly on the alkaline side of neutral (pH7.0). Horticultural or hydrated lime - calcium hydroxide - must NOT be used in any circumstances as this does have a strongly alkaline reaction and will damage the roots of plants. Dolomitic limestone, which is comprised of both magnesium and calcium carbonates, may be used with advantage as a provider of both calcium and magnesium as soluble bicarbonates.
Ariocarpus hate peat and similarly based composts as a long term growing medium, particularly in maturity. Although they may seem to do well in it for a short time the ultimate result will be poor root structures, loss of roots and generally unhealthy looking plants - this is very obvious in A. trigonus as the tubercle tips yellow and die back. The plants do somewhat better in proprietary loam based composts with added grit. The problem with these is that their quality is very variable from different commercial sources and most of them contain some peat. The authors, strongly influenced by the habitat conditions, use a soil comprising, by volume, 30% heavy clay loam, 50% coarse grits (size range 1 to 6mm) and 20% limestone chippings (4mm). A soil with this type of composition is free draining dries out reasonably quickly and does not become a soggy mass when wet. The proportion of ingredients used in these mixes is not too critical and may be varied to suit local conditions. In a hot dry climate, where pots dry out quickly, it may be desirable to increase the percentage of loam and decrease the quantity and possibly the particle size of the grit. Some pumice or similar inert porous material may be used to substitute for part of the grit and a slow release granular high potash fertilizer may be added with advantage.
Experience has shown that Ariocarpus grow very well in this medium over an extended time scale - the top growth is clean, sturdy, firm and true to type and the root structures are very well developed, often to the point that they bulge plastic pots and push soil and top dressing out of the top - and this is the only time to repot! There isn't a right time to repot - repot plants when they need it, but preferably during the winter dormancy period - but use dry compost if you do it then. This was never the experience with other soil mixtures! Plastic pots are preferred to clay pots for the reasons discussed below.
Apart from their lower cost and weight, plastic pots are preferred to clay because hair roots do not stick to the sides and the pots expand to some degree to accommodate a developing root structure and are 'warmer' If the plant is healthy and there are no signs of pests or disease, 'potting on' with as little disturbance of the soil ball - boot structure as possible, is much preferred to removal of all the soil. Simply remove the plant from the old pot - this may entail cutting the pot off carefully for the above root size reason (something you can't do with a clay pot without smashing it!), shake off any loose soil and fill the bottom space and annular space between the root ball and the new pot with the same sort of compost, tap down by bumping the pot on the bench and top dress if you wish. With pots of a diameter larger than 6-7cm shallow half pots are preferred unless the plant has a long taproot. Even in the case of a mild infection of, say, root mealy bug, it is better to pot on and treat the infection, after a dry quarantine of a week, with a systemic insecticide rather than disturb the root ball.
Watering and Feeding
The frequency of watering is very dependent on many other factors such as the soil type and porosity, temperature and the level of ventilation, and most importantly whether the plants are in active growth of not. With the soil described above plants will require watering on average about every two weeks throughout the growing season of late March to mid-October in Britain. Within this average are a lot of variables in terms of the growth pattern of the plants and the weather conditions. Ariocarpus are early and late season growers and tend to go semi-dormant in the middle of the summer and the water demand follows this trend. The need for water is at its peak from mid-spring to early summer and again in late summer prior to flowering. If these periods correspond with a period of hot dry weather the plants will dry out much more quickly and may need watering every few days. After flowering has finished, generally by early November, the plants should be dried out completely for a long winter dormancy until early spring. In hotter, drier climates more frequent watering will be required and the periods of active growth, dormancy and flowering will be affected by a longer growing season.
The quality of water is probably important but we have no definite evidence for this. In general rainwater is preferred to mains water, as it avoids the high levels of chlorination found in some supplies. One of us has a limestone gravel filter bed fitted to the inlet of the rainwater storage system. This has the dual benefit of removing debris from the supply and removing some of the dissolved acidic gases such as carbon dioxide, oxides of sulfur and nitrogen at the same time putting a small amount of soluble calcium into the supply as the bicarbonate, sulfate and nitrate. This water is used on all the plants, not just the Ariocarpus, without any adverse effects and possibly with some beneficial effects. The primary water container from which watering is carried out is best housed in the greenhouse so that the water is slightly pre-warmed.
Plants are best placed permanently in large shallow trays on the staging as this facilitates bottom watering which is generally preferred to top watering. The amount of water added to a tray should be that which is be soaked up in about 30 minutes. For a 60cm x 60cm tray close packed with potted plants this is about a 2cm depth. The advantage of bottom watering is twofold, the collar of the plant does not get too wet thus minimizing the risk of rot and the wool on the plant is kept in nice condition as it does not get washed down and matted. Bottom watering has one disadvantage as it causes, after a period of time, salts to crystallize on the top surface of the compost or top dressing. This can be avoided by occasional careful top watering and by light spraying.
Feeding and bug control are best carried out in parallel with watering by putting fertilizer and/or systemic insecticide in the water supply. Feeding is best done at each watering using a high potash (15N 15P 30K) or a high phosphate and potash (12.5N 25P 25K) soluble feed, containing essential trace elements, at a quarter of the recommended concentration. Precautionary bug control should be done twice yearly using a systemic insecticide added to the water in spring and in late summer. Unlikely and minor infections at in between times are best dealt with using different insecticides such as Malathion or nicotine in alcohol.
Light, Heat and Ventilation
Actively growing plants need all three of these in abundance to produce strong healthy growth and good reliable flowering but this must be coupled with a healthy and vigorous root system and a properly controlled watering and feeding regime. Gone are the days of the dry and dusty brigade with dry shriveled fossils that did not grow and did not flower who 'grew' them in little more than crushed brick and were frightened to water them more than once a year. Plants need proper conditions to thrive even in habitat. The photograph shows two A. fissuratus plants growing near Lajitas in the Big Bend, Texas. The plant on the left is in a more barren fully exposed position and is clearly suffering. In contrast the plant on the right has a little shade from the Agave lechuguilla, probably a more stable water and nutrient supply and looks plump and healthy. Clearly so much rubbish is talked about 'growing plantshard' and keeping them 'typical' - what is 'typical'?
The best possible source of heat and light is sunlight and optimum results are obtained by placing the greenhouse in the sunniest position in the garden with its long axis in an east-west direction and by keeping the glass clean. Some growers put shading on the glass but this is unnecessary and undesirable in Britain and northern Europe, although it may be needed in hotter, sunnier climates. It is possible to damage plants by burning even in Britain, but this will not happen provided that the plants are acclimatized to high light levels, have good root systems, are adequately watered and there is good air circulation from open vents and electric fans.The plants do not need high temperatures during the winter dormancy period, a minimum of 4C is more than adequate provided they are kept totally dry. The tricky times are the post flowering period up to mid to late December when the plants may not be fully dry at the root and after the first early spring watering. At these times it is strongly advisable to hold a minimum temperature of 10C.
Winter heating is best done with an electric fan heater that warms and circulates the air or with some other heater where the products of combustion of oil or gas do not enter the greenhouse atmosphere. The products of combustion of these fuels are almost exclusively carbon dioxide and water vapor which is undesirable at this time of the year. Water vapor, marginally more of which is produced from gas than from kerosene, adds to the humidity burden and may help promote rot and fungal infection. A note of caution however if you use electric heating a back up system is advised in case of a power failure and this, of necessity, will probably have to be fuelled by gas or kerosene
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