Succulents might make good choices for a beginner's indoor garden, but they are not entirely fool-proof. This large family of plants contains familiar as well as exotic cousins, native to mostly arid climates ranging from the Arctic Circle to the Mountains of Chile. If their leaves begin to drop, the cause can vary widely from species to species.
Succulents are characterized by their water-retentive leaves, generally with a low surface-to-volume ratio and thick cuticle, or skin. The smooth, oval leaves of the jade plant (_Crassula ovata_), hardy only in U.S. Department of Agriculture plant hardiness zones 11 though 12, bear little resemblance to the flat, spiny leaves of the prickly pear cactus (_Opuntia compressa_), hardy in USDA zones 4 through 9.
The prickly pear cactus also produces a large, yellow bloom in summer, followed by red fruit in fall, but its jade plant cousin needs more than indoor light to produce tiny white or pink flowers in spring. Both, however, have Crassulacean acid metabolisms, which control transpiration and trap moisture inside leaves.
Although many succulents share Crassulacean acid metabolism, the family consists of more than 60 genuses that live in varying environments. Cacti, a genus containing more than 2,000 species, live in desert conditions, while Bromeliaceae, which contains more than 3,000 varieties, live in tropical climates.
Diagnosing your succulent's leaf drop relies on finding out its genus and species. A succulent society or garden club can be a source of information for a succulent plant's environmental needs.
Natural Leaf Loss
Succulents conserve moisture, so too much water can cause rot in leaf petioles -- the connective tissue between leaf and stem -- that can lead to leaf drop. A sudden drop in temperature or drafts can interfere with metabolism functions, decreasing the need for water retention, which can result in leaf drop.
Allowing soil to dry between watering and keeping plants out of cold drafts can limit leaf drop, but grassy bromeliads and jade plants drop older leaves as new ones emerge, a process that cannot be stopped.
Although succulents are relatively disease and pest-free, landscape agaves (Agave spp.), with cultivars hardy from USDA zone 7 through 12, may be bothered by agave snout weevils or coccid scale, known as soft scale. Weevils attack the crown of the agave, resulting in the collapse of its sword-like leaves.
Scales suck nutrients from leaves. Plants that have collapsed cannot be saved, but infestations of snout weevils might be prevented by a single spring application of a broad-spectrum insecticide. Acephate, a systemic insecticide, kills scales and is available for home use in powder form, to be mixed 2 to 3 tablespoons per gallon of water and sprayed every seven to 10 days.