Sometimes, cacti have wide ribs and little spine protection and then sunburn will occur in between the ribs. A light burn will just be a whitish discoloring on the exposed areas. More severe burns will become a hard brown scar along the plant in whatever areas did not get shaded by spines or other parts of the stem.
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| source pic: debraleebaldwin.com |
Treatment
If you catch a sun burned succulent at the whitish discoloring stage, you can undo the damage by getting it some shade protection. If the plant gets to the brown scaring stage, then the damage is permanent and the plant will have to grow out of it in time. Again, prevention is the best defense with sunburn.
If you purchase a succulent plant that has been sitting inside a store for some time, you will need to gradually move it into full sun. Do this by giving it full sun for a short period of time each day, and then regularly increase the length of time in the full sun over the course of a couple weeks.
Keep in mind that some species do not ever want full sun all day. Also note that “full sun” in England is much different than “full sun” in Arizona. The stronger the sun where you live, the more careful you have to be to keep your plants sun burn free.
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