Succulents respond to many environmental stressors by stopping growing and dropping leaves, reducing their energy needs. Heat, frost, low or high light, chemical shock, and improper watering can often cause leaf drop suddenly.
Temperature
Because most succulents are adapted to hot, arid areas where prolonged periods of heat are the norm, they drop leaves when stressed by heat or drought. Although this is relatively normal, keeping succulents in the shade when temperatures soar will help prevent this. Watch them closely: move them or place a shade cloth over them if they look wilted or sunburned. The opposite problem also occurs: succulents do not do well in freezing conditions, which may blacken and burn their leaves. Sometimes, these will fall off, but usually not until the plant grows new leaves to replace them, so resist the urge to peel off these protective dead leaves.
Light
Succulents need enough light, especially since they are typically adapted to areas with year-round full sun. They do best in brightly lit areas; when light is lacking, they turn light green or yellow and become straggly, trying to grow toward the light. If the problem is not corrected, they will eventually drop leaves or die. Low light is not the only problem. Succulents moved to a new area without acclimation or suddenly rotated in a bright spot may get a sunburn. Make changes slowly, and wait for plants to adapt before moving on.
Using Chemicals
Shocking a succulent's system can also cause leaf drop. When succulents contract diseases or fungal infections, responding immediately and forcefully is tempting, but you must be careful. Always read package directions thoroughly when using chemicals, and do not reapply more often than the label recommends. Always make sure your succulent is not environmentally stressed before applying chemicals.
Watering
Succulents are known for needing little water, but too little will cause them to wilt and fail to thrive. You must be careful not to overwater them. Giving succulents too much water too often will cause their leaves to swell, and if they do not get a chance to dry out, they will drop off the plant. Wait until the soil is almost completely dry and the leaves look a little limp before watering. Water thoroughly until you see trickles coming out of the bottom of the pot. Always use pots with drainage holes.
Source: sfgate.com
Links
- Succupedia: Browse succulents by Scientific Name, Common Name, Genus, Family, USDA Hardiness Zone, Origin, or cacti by Genus