San Pedro (Trichocereus pachanoi) is a sun loving cactus. While they can be grown indoors, they will not grow as thick and robust as those grown outdoors. Ideally, mature cacti should receive 4 to 6 hours of direct sunlight per day, making outdoor cultivation the best option when possible.
In this guide, we’ll cover the light requirements for San Pedro Cactus at different stages of growth, helping you grow healthy seedlings and mature plants indoors or outdoors.
Light for Seedlings
Although San Pedro is a sun lover, the seedlings are highly sensitive to light. Exposing them to full sun or placing them too close to high-powered grow lights can cause them to burn, stunting their growth. Seedlings grown outdoors should be kept in indirect sunlight or under a shade cloth. If growing indoors they should be placed under weak lighting (fluorescent lights are often enough).
Personally, I like to start mine indoors under lights, so I can closely monitor their progress and adjust the height of the lights as needed. This gives me full control to ensure the young cacti don’t get stressed. Healthy seedlings should remain bright green. If they begin turning reddish in color, they are being burned and the lights need to be moved farther away.
In the picture below, you will see an example of Peruvian Torch seedlings that have been exposed to too much light and are burning. Seedlings in this state will grow extremely slowly.
Transitioning Older Cacti to More Light
Once your San Pedro cacti are a couple of years old, they can tolerate more intense light. If you’re keeping them indoors, this is the point where you’ll want to move them to high-output LED grow lights, a bright south-facing window, or even a combination of both. I use Spider Farmer grow lights because they offer high-quality components at an affordable price. Start with the light positioned a few feet away, then gradually move it closer over several weeks to prevent burning.
For thick, robust growth, San Pedro cacti are best cultivated outdoors. At this stage, gradually begin acclimating your cactus to direct sunlight, starting with a half hour to an hour at first and slowly working your way up to 4–6 hours per day. This transition is important, as suddenly placing a cactus in full sun can shock or burn it.
Winter Dormancy
San Pedro cacti are not frost-tolerant. In areas that experience winter they must be grown in pots and brought inside during the colder months. During this period they should be made dormant. Dormancy is a resting phase when growth stops and the cactus conserves energy until spring. Cacti do not require light while in this dormant state. You will find a full guide to dormancy HERE.
Final Thoughts
With proper lighting at each stage, your San Pedro cactus will reward you with strong, healthy growth. Whether growing indoors under LEDs or outdoors, it’s essential to closely monitor your cacti during the seedling stage and while transitioning to full sun for any signs of stress.
San Pedro cacti will recover quickly from sun damage but without taking action they will remain stressed causing them to grow slowly. Paying attention to their needs and carefully adjusting light exposure will help your San Pedro cactus flourish at every stage of growth.