Unpack your Trichocereus cactus as soon as possible, and for the first two weeks place in an area which receives bright filtered, non-direct light. After this acclimatisation time, it is time for the first watering, and the gradual introduction of more intense light.
Trichocereus cacti prefer it hot and sunny and grow extremely fast (up to 40cm in a year) when watered every week or two during the growing season, but must only be watered once the soil mix has been dry for at least three days. During the colder months, watering should cease, allowing the cactus to go dormant until the growing season starts again.
Most Trichocereus cactus growers use a mix of sand, peat, limestone, blood meal, bone meal, potting soil, animal faeces, vermiculite or perlite – the aim being to avoid encouraging common hazards such as nitrogen burn, saline dehydration, and rot. For the casual Trichocereus gardener, we recommend growing the cacti in an equal mix of John Innes No.2 or generic cactus soil (available from most garden centres – make sure to break up/sieve out any large organic matter) and perlite (or similar volcanic rock). We also recommend adding a 1-2cm layer of stones or clay pot fragments at the bottom of the pot, to assist with drainage.
All cacti benefit from occasional dosage with low nitrogen, high phosphorous fertilizer, as this promotes root development and proper tissue consistency. While high nitrogen fertilizer will dramatically increase the speed of growth, it may also cause the cacti to swell, split, and/or become hollow, damaging the plants and reducing their survival rate during the colder months.