Amount of Sunlight for a Cactus

Ideal Sunlight Amount

• Cacti do not photosynthesize with traditional leaves, but use their green stems and trunks to create energy for growth and reproduction. Ideal sunlight amounts vary widely between species. In general, most cacti prefer full sunlight -- 6 hours of sunlight or more everyday with morning exposure being the best scenario. Afternoon sunlight, even for a cactus, can be damaging over time. One key signal that your cacti are well-situated in your garden is flowering. Producing a flower requires a lot of photosynthesis energy along with reduced stress from heat and drought. If your cacti flower periodically, they are properly naturalized into your landscape.

Excessive Sunlight

• If your cacti appear to be whitening, they are exposed to excessive sunlight. In fact, plant cells are dying off when cacti have white, yellow or orange scars. Referred to as scorching, these scars do not typically heal -- the off-color remains for the plant's entire life. This scorching typically occurs if you move the cactus from a shady area to a full sunlight location. Alternatively, acclimate your cactus to the new location by slowly moving it into the sun for short periods at a time. This hardening process reduces scorching occurrences, but confirm that your particular cactus variety can thrive in full sunlight conditions because all cultivars have different needs.

Shady Conditions

• Locating your cactus in heavy shade causes it to stretch up or even to the sides; it is searching for any sunlight to photosynthesize. If you see an unusual elongation of stems, you need to move the cactus into a brighter location. Cacti provide their own unique shading strategy using their spines. Commonly white, spines are modified leaves that provide some reflective properties to move heat away from the trunk. Some varieties have white hairs to reflect even more sunlight away for heat stress relief.

Indoor Lighting

• You can grow potted cacti indoors as long as they have access to sunlight or artificial light. For example, place your cacti in a west- or south-facing window for indirect, but bright, sunlight. If you do not have a prime window location, simply hang fluorescent lights above the cacti. Two 40-watt bulbs running up to 6 hours a day should provide enough light for healthy growth.