Cacti can take on a yellowish colour when exposed to too much light. While numerous species of cacti thrive in light, intense light can cause major health problems. It is important when growing cacti to be able to diagnose the signs of too much light exposure to provide the best growing environment for your cacti.
Too Much Light
The amount of light your cactus needs depends on the species. However, you can judge how much light your cactus needs by monitoring it for discolouration. Cacti that turn yellow, orange or take on a bleached-out appearance have been exposed to too much light. A healthy cactus will maintain its colour. If a cactus is moved from moderate light to intense light, it may get scorched by the sun. A scorched cactus produces a discoloured ring around the top, which will not go away.
Cacti need full sunlight to grow. Full sunlight is characterised as a location that receives six to eight hours of sun a day. Typically, areas in the southern part of the yard will receive enough light to support a cactus. If you are bringing your cactus outside from overwintering indoors, place the cactus in a low light area for a few days. Gradually, increase the light every few days for your cactus. Cacti that discolour should be moved to a lower light area.
Sticking a cactus in your window can cause yellow discolouration. Windows, especially if they are south facing, may cast too much direct light on the cactus. Place a sheer curtain over the window. Monitor the cactus for any discolouration. You can also move the cactus further away from the window if it looks stressed. Gardeners may find that placing a cactus inside the home involves trial and error, as cacti species differ in the amount of sun they need.
To Little Light
When choosing the best area for your cactus, it is important to recognise signs that your cactus isn't receiving enough light. Cacti that grow towards light sources need to be moved closer to the light. If the stem of your cactus is actually reaching out for the window, gradually bring the cactus closer. To restore the shape of the cactus, rotate the plant every week so that it receives light from all sides of the plant.