The common name “geranium” refers to a popular garden plant, often grown in containers and window boxes for its season-long blooms. The plant’s drought tolerance is complex and depends heavily on the specific botanical group in question. While many assume these flowers require regular moisture, the most commonly cultivated varieties possess a surprising resilience to dry conditions. Understanding this requires clarifying the plant’s true identity, as the plant commonly sold as a geranium is botanically distinct from its perennial namesake.
The Critical Difference: True Geraniums vs. Pelargoniums
The confusion stems from an 18th-century botanical misclassification that placed two separate genera into the same group. The annual or tender perennial plant most people recognize as a geranium actually belongs to the genus Pelargonium. These Pelargoniums are native to the arid and warm temperate regions of South Africa, a heritage that predisposes them to heat and drought tolerance.
The other, less common, group is the true Geranium genus, often called Cranesbills or hardy geraniums, which are cold-hardy perennial plants. True Geraniums typically originate from the temperate zones of the Northern Hemisphere, where their natural habitat provides more consistent moisture. Their flowers display five symmetrical petals, unlike Pelargonium flowers, which are asymmetrical. This difference in origin and flower structure is fundamental to understanding their distinct water needs.
Drought Tolerance Levels by Type
The Pelargoniums—including Zonal, Ivy-leaved, and Scented types—exhibit moderate to high drought tolerance once their root systems are established. Their survival mechanism is a result of their South African ancestry, where they evolved specific xerophytic adaptations. They often feature thick, fleshy stems and waxy leaves, which function as water storage organs, allowing the plant to sustain itself during dry spells.
Ivy-leaved Pelargoniums (P. peltatum) are notable for their thick leaf cuticles, which significantly reduce water loss through transpiration. While they can survive periods of water shortage, their flowering performance may diminish without supplemental moisture. Allowing the soil to dry out between waterings is preferred for Pelargoniums to prevent root rot, which is a greater threat than temporary dryness.
For true Geraniums (Cranesbills), drought tolerance varies widely by species. Many varieties require medium-moisture soil and may suffer from wilting foliage during prolonged heat. However, specific species are highly resilient. Geranium macrorrhizum, or Bigroot Geranium, is often cited as the most drought-tolerant of the hardy types. This resilience is attributed to its thick, rhizomatous root structure, which stores resources and helps the plant survive in drier conditions and even dry shade. Geranium sanguineum (Bloody Cranesbill) is another robust perennial that tolerates some drought once established.
Watering Strategies for Dry Conditions
To maximize the natural drought tolerance of geraniums, especially Pelargoniums, watering technique is paramount. The most effective method is deep, infrequent watering, which encourages the plant’s roots to grow deeper into the soil. This deep root system makes the plant less reliant on surface moisture and better equipped to handle dry conditions.
Before watering, check the soil moisture by inserting a finger one to two inches deep. If the soil feels dry at that depth, water thoroughly until the moisture drains from the container bottom or fully saturates the root zone in the ground. This ensures the entire root ball receives hydration, rather than just the topsoil.
Applying a layer of organic mulch around the base of the plant can significantly reduce surface evaporation, helping to keep the root zone cooler and conserve existing soil moisture. When watering, aim the stream directly at the soil beneath the foliage, avoiding overhead watering. Wet leaves increase the risk of fungal diseases like botrytis, particularly in humid environments. Container-grown plants require more frequent checks than in-ground plants, as their limited soil volume dries out much faster, sometimes needing water every one to three days during extreme heat.