Short answer
Aloe vera leaves usually fall off because the plant is suffering from root rot caused by overwatering, which weakens the leaf base until it detaches. To fix this, stop watering immediately, check the roots for decay, and transplant into fresh, well-draining succulent soil.
When an Aloe vera leaf falls off, it is a significant warning sign that the plant's structural integrity has been compromised at the base. While older, outermost leaves naturally shrivel and die, leaves dropping while still plump or mushy indicates a serious health issue that requires immediate attention to save the remainder of the plant.
Aloe vera plants are desert succulents evolved for drought, so excess moisture trapped in the soil leads to fungal decay. When the roots rot, they can no longer support the leaves, causing them to turn soft, translucent, and eventually drop off.
Check: Gently pull the plant out of its pot; if the roots are dark, mushy, or smell foul instead of firm and light-colored, rot is present.
Fix: Trim away all rotted roots, let the plant air-dry for a day, and repot in a fresh, gritty cactus mix in a pot with large drainage holes.
If water is poured directly into the center of the rosette or allowed to sit on the leaves, moisture settles at the base of the stem. This causes localized rot that eventually severs the connection between the leaves and the plant core.
Check: Check the center of the leaf rosette for dark, sunken, or slimy patches where the leaf meets the central stem.
Fix: Use a sterile blade to cut away the rotted tissue, keep the plant in a dry environment with high airflow, and water only the soil line hereafter.
While Aloe is drought-tolerant, extreme, long-term lack of moisture causes the plant to cannibalize its oldest leaves to survive. These leaves will thin, curl, and turn crisp before dropping.
Check: Observe if the leaves are paper-thin and shriveled rather than mushy or translucent.
Fix: Deeply soak the soil until water runs out the bottom, then resume a schedule of watering once the soil is completely dry throughout the pot.
When to worry
You must act immediately if leaves are dropping; if the stem itself feels soft or mushy when squeezed, the rot has likely reached the crown, which is often fatal for the plant.
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Diagnose my Aloe VeraUsually, no. If the leaf fell off due to rot, the base of the leaf is likely infected and will turn into mush rather than rooting. It is best to discard it.
Do not fertilize a stressed or rotting Aloe. Fertilizer can shock the damaged root system and accelerate fungal growth; wait until the plant shows signs of new, healthy growth.
Forget a calendar schedule. Use a bamboo skewer to check that the soil is 100% dry at the bottom of the pot before watering, which usually takes about three weeks depending on your home's light and temperature.
Consistent with guidance from: The Royal Horticultural Society, University of California Cooperative Extension.