Lithops, often called "living stones," are fascinating succulent plants native to the arid desert regions of South Africa and Namibia. Their unique survival strategy involves mimicking the appearance of stones to avoid predation and thriving in some of the harshest climates on Earth. To successfully cultivate them indoors in the diverse climates of the USA, it is paramount to understand and replicate their ideal temperature and humidity cycles, which are intrinsically linked to their growth and dormancy periods.
For Lithops, the primary growth period is not summer but autumn. As temperatures begin to moderate from the summer heat, Lithops break their dormancy and initiate a burst of growth, often culminating in the production of daisy-like flowers. During this phase, ideal daytime temperatures should range between **70°F and 80°F (21°C - 27°C)**. A slight drop in temperature at night is not only acceptable but beneficial, mimicking their natural desert habitat where days are warm and nights are cool. Nighttime temperatures can comfortably drop into the **50s °F (10-15°C)**. This period requires the most attention to light; they need several hours of direct sunlight daily (a south-facing window is ideal) to maintain their compact form and encourage flowering.
Lithops have two distinct dormancy periods that must be respected for long-term health. Their **summer dormancy** is triggered by high temperatures, typically above **90°F (32°C)**. During this time, the plant's metabolic processes slow dramatically. It is vital to reduce watering significantly and provide bright, indirect light to prevent overheating in a small pot. Conversely, **winter dormancy** is triggered by shorter days and cooler temperatures. While they can tolerate brief dips near **freezing (32°F / 0°C)**, it is not advisable. A safer winter temperature range is between **50°F and 65°F (10°C - 18°C)**. During both dormancy periods, the plant is not actively growing and requires very little to no water.
Perhaps more critical than temperature is humidity control. In their native environment, Lithops are adapted to extremely low atmospheric humidity. Indoor humidity levels should be kept **below 50%**. High humidity is a primary cause of rot and fungal diseases in Lithops, as their succulent tissues are not designed to handle moist air. This is a significant challenge in many parts of the USA, particularly in the humid Southeast and Midwest during summer. To combat this, ensure excellent air circulation around your plants using a small fan. Avoid placing them in naturally humid rooms like bathrooms or kitchens. A well-draining, gritty substrate composed mostly of inorganic materials like perlite or pumice is non-negotiable, as it prevents water from pooling around the sensitive root neck.
Watering practices are dictated directly by temperature and humidity. Water should only be applied during the cool-season growth period (autumn and early spring) and only when the soil is completely dry. The golden rule is to water based on the plant's cues: a slight shrinking or wrinkling of the top surface indicates it is ready for a deep drink. During the hot summer and cool winter dormancies, the plant must be kept almost entirely dry. High humidity completely negates the need for watering, as the plant can absorb minimal moisture from the air.
