The San Pedro cactus (Trichocereus pachanoi) is native to the rainy western slopes of the Andes Mountains in Peru and Ecuador. It has become adapted to wetter-than-normal conditions for a typical cactus, and can survive drops in temperature down to -9.44 degrees C. This has made it a popular landscape plant in the American southwest. The San Pedro cactus is easy to care for, tolerant of neglect and can be started from seed by the home gardener.
Mix 1 part perlite and 1 part peat moss thoroughly. This is a good basic seedling starting mix for cacti.
Fill the plastic pot to about half an inch below the rim with your newly mixed seedling soil. Small 2-inch pots work well for only a few plants. If you have a lot of seeds use a nursery tray. The pots should have good drainage holes and be wider that they are deep. San Pedro cactus roots spread a little more laterally rather than down like other plants.
Sprinkle the San Pedro cactus seeds lightly and evenly on the surface of the potting mix.
Cover the seeds with a very thin layer of sand about equal to the diameter of the seeds.
Set the entire pot in the bucket or large bowl and fill the bowl with water to about half way up the seedling pot. This allows the seedling soil to absorb the water slowly from the bottom without disturbing the seeds on the surface. Avoid splashing the surface of the soil or watering it directly.
Remove the seedling pot from the water when the soil has absorbed enough for the surface to be moist. Let the excess water drain out of the bottom of the pot.
Fit a plastic bag over the top of the seedling pot forming a mini-greenhouse to hold in the moisture. If you are using a nursery tray, use the prefabricated clear domes for seedlings.
Place the pot in a warm bright location that is away from direct sunlight. The seeds will sprout in about one to two weeks. As the new San Pedro cacti start to sprout, poke a few holes in the bag every day or so until the bag has so many holes it is no longer effective at holding moisture in. Then the bag can be removed entirely. This helps slowly acclimate the young seedlings to atmospheric air over a week or two and prevents drying and sudden death. Seedlings are ready to transplant into individual pots when they are about half an inch in diameter.
Sowing San Pedro cactus is best done during the spring and summer because they have a natural winter dormancy period where growth slows or even stops. The optimal temperature for San Pedro cactus seed germination is between 15.5 and 21.1 degrees C during the nighttime. You can start seeds indoors during cooler months or outdoors under a protected areas such as a covered patio in the spring and summer. Wait until the seedlings are transplanted into individual pots before acclimating them to full sun to ensure they are well established. San Pedro cacti prefer a little more water than most types of cacti and should only be allowed to dry slightly between waterings. In the winter during dormancy, only water enough to keep the cactus from shrivelling until growth begins in the spring.
Direct sun during germination will overheat the soil and cause dramatic temperature differences that may kill the seeds or prematurely dry out the soil. Never let the soil remain wet or water logged. San Pedro cacti need very well-drained, airy soil or the roots will rot. In southern latitudes such as in the American southwest, mature San Pedro cacti need to be protected from full direct sun in the summer or they will burn. 25 per cent shade will prevent burning. In northern latitudes, they need to be protected from temperatures below -9.44 degrees C and should probably kept indoors during winter.