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San Pedro are different than most columnar cacti in that they grow very rapidly, and enjoy a somewhat richer soil mix and more frequent waterings than most cacti. They are quite hardy, and will grow successfully in a wide range of conditions. The mescaline content in these cacti apparently are a defense mechanism against invading organisms, and increase during stressful conditions, particularly when the cacti are underwatered.

Lighting

Growth of these cacti occurs mainly during the brightest months of summer. In locations where intense, bright sunny days occur for only a few months, they will not grow rapidly. Growth can be greatly stimulated with high intensity plant growth lights such as used for marijuana cultivation, but year round operation of these 1000 watt bulbs can be very expensive. Ideally, angled lighting from both sides should be observed to allow full illumination along the entire column. When underwatering to increase potency, the cacti should be placed in a less exposed location, with partial shade. If the lighting is too bright for maximum potency increase (but not for maximum growth) the cacti will turn a lighter shade of green. This response occurs after only a few weeks, so adjust the lighting to achieve a darker shade of green.

Soil

San Pedro should be planted in very porous soil. A typical cactus potting soil mix is OK, but can be improved by addition of extra pumice. The more porous the soil mix, the more frequently the cacti will have to be watered, and the less danger there will be of root rot and other problems of over-watering. However, the soil mix should also be fairly rich. Cactus are damaged by high nitrogen contents, so be sure to use a fertilizer with low nitrogen. Don't begin this treatment immediately after repotting; let the roots set in. When attempting to increase potency, this feeding is not necessary since the cactus will not be receiving water.

Potting

These cacti like to send out far ranging lateral root systems near to the surface, so if potted they should be placed in very wide clay pots. Deep but narrow pots will result in stunted growth. Clay pots are required for proper drainage. Use of large clay pots is in many ways preferable to planting directly in the ground, since the watering, drainage, and feeding can be controlled more precisely. However, if attempting to increase potency, the cactus can be placed in small, constricted pots since good growth conditions are not desired. In any case, repotting San Pedro should not be idly done since it shocks the root system and injures the cactus. It is best to choose a suitable pot and stick with it.

Watering

When in full growth, the cactus should be watered quite frequently. The cactus should be watered when the subsurface soil is not damp to the touch. This will depend on many other factors. At one extreme, for a cactus in very well-drained, high pumice soil, potted in porous clay pots, receiving bright full sunlight all day long, in an exposed, windy, hot location, the cactus can be thoroughly watered every four days. If fed this frequently, the plant food concentration should be halved. One way to test soil dampness is to insert a small, clean redwood stake into the soil. If it comes out with small particles of sand clinging to it, the soil is still moist and should not be watered. During dormant winter months, the cactus should be watered much less frequently, perhaps once a month or so. This will stimulate root growth and result in faster growth during the hot season. As mentioned above, when attempting to increase potency, the cactus should not be watered at all for an entire growing season, and placed in a less exposed, partially shaded location.