I've grown hundreds of varieties of succulents for decades in my inland Southern CA garden. I've noticed that excessive heat and sun can do as much damage as midwinter frosts. Use the summer care tips here and in my video to keep your own succulents healthy when the heat hits.
1. Shade any smooth-leaved succulents that are not from the desert Southwest
Unless you live in a mild, maritime location, those that I call "the pretty little ones" need protection from scorching summer sun. Ideally they'll get several hours of early morning or late afternoon sun, and bright or dappled shade the rest of the day. (See how I define Types of Shade.) If need be, throw a sheet or shade cloth over exposed aeoniums, aloes, echeverias, kalanchoes, and the like.
2. Protect young desert plants
When established, most cacti, yuccas, agaves and other succulents native to Mexico and the Southwest sail through summer. However even in their native habitats, young cacti grow beneath "nurse plants" that shelter them from harsh conditions.
3. Give cold-climate succulents preferential treatment
Rock-garden plants such as sempervivums (hens-and-chicks) and sedums (stonecrops) thrive in the northern and eastern US and in Europe. Farther south, these can go downhill when temperatures rise above 80 degrees F. Keep them shaded and cool. Exceptions are sedums (and Sedum crosses such as graptosedums) that have fat, thumb-sized leaves and that turn vivid shades of red and orange.
4. Monitor soil moisture
Soil that goes bone dry may not kill thick-leaved and -trunked succulents, but if fine root filaments desiccate, growth will slow or cease. In pots you can test soil moisture by inserting a chopstick; if soil clings, it's moist.
5. Soak plants before leaving town
Generally if other conditions are met, succulents won't miss you if you water them well before you leave, then again when you return. As an extra precaution in case temperatures rise significantly while you're gone, move potted succulents into shade.
6. Don't stress over your succulents
Gardening is a process, and sometimes the only way to know what will do well is to lose a few plants. Weather extremes lead to valuable lessons. Consider any casualties as annuals, and fill gaps when weather cools.
See the video
Related info on this site
Don’t let summer sun and heat harm your succulents! Heat generally isn’t a concern. Although some succulents (like sempervivums) tend not to thrive in temps above 80 or 90 degrees F, the majority are fine. It’s heat plus sun that’s the concern.
You have two options for protecting your succulents from heat waves that follow cool weather:
1. Move them. Of course this is only possible if they’re in pots. But don’t forget to do it! When sudden heat and sun hit, succulents that haven’t had time to acclimate may sunburn. There’s no reversing the resulting brown or beige patches.
Late summer is when tough succulents really shine. Large agaves handle summer heat, and are unfazed by harsh sun, high temps and lack of rain. Their statuesque, fountainlike forms lend a sculptural element to any landscape, and contrast beautifully with fine-textured ornamentals. They also make good firebreak plants and security fences. With the exception of a few…
Why do I love cacti? It’s a natural progression: As we gain appreciation for the lines, textures and shapes of succulents, we arrive at those that exhibit elegant simplicity—never mind that they have spines (in fact, sometimes because they do). Here are a dozen reasons.