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Cactus and UV light #241022
Asked May 01, 2015, 5:45 PM EDT
Last summer the cactus did not do well because the hot sun was too much for it -- even though I watered it weekly. I tried moving the cactus to another spot on my patio that got morning sun and afternoon shade, and it seemed to do better. When fall arrived, I moved it indoors and placed it on a stand next to a west / southwest-facing window. During the winter I watered it approximately once every 3-4 weeks. It seems to have "survived OK," but I can't tell if it is still growing and/or healthy!
Last year we purchased new energy-efficient windows, which block UV light. I was wondering if cacti -- or any other plant, for that matter -- needs UV light to thrive and grow? Can my cactus still grow if I always keep it indoors behind UV-blocking glass? Or do I need to keep it outside year-round? Any assistance you can provide would be most appreciated. Thank you!!
-- Marsha Reeder, Aurora, CO
Arapahoe County Colorado
Expert Response
Here is some general information about maintaining the overall health of barrel cactus:
Cacti generally like to be slightly pot bound and should only be repotted as needed. Repot in April before summer growth begins. After repotting, wait several days before watering. Also, if the new container is too large, the soil may stay too moist and lead to rot.
Use a low nitrogen fertilizer such as 5-10-5 once a month from June through September. This is the active growing season for cacti, so keep them watered so the soil does not dry out.
Preferred temperatures are around 75°F during the growing season. They can be moved outdoors during the summer, but place them in partial shade (morning sun, afternoon shade) for the first month so as to not shock the plant.
After the active growing season, they can be brought indoors and placed in a cool (preferably about 45-55°F), but sunny room near a east or west facing window. Dormant cacti should be watered approximately every 3 weeks.
General information can be found at these helpful links:
http://www.clemson.edu/extension/hgic/plants/pdf/hgic1502.pdf
http://www.ext.colostate.edu/ptlk/1306.html
http://www.ext.colostate.edu/ptlk/1329.html
Finally, the Colorado Cactus and Succulent Society may likely be able to help you with your specific question about UV levels. They are an organization which purposes to educate the public on all things cactus. http://www.coloradocactus.org/
