The plant most people call a “geranium” is actually a warm-weather tender perennial belonging to the genus Pelargonium. Native to warm temperate and tropical regions like South Africa, these plants are intolerant of cold temperatures. Because they cannot survive frost, they are typically grown as annuals in most temperate climates. Their active season is dictated by the absence of frost and the need for consistent warmth.
Peak Blooming Period
Once established, these plants are known for their long flowering season, spanning from late spring until the first hard frost of autumn. They are continuous bloomers, producing bright, showy clusters of flowers that consistently replace spent blooms throughout the summer months. This active period typically begins in May and can last through September or October, depending on the local climate.
In warmer regions, specifically USDA hardiness zones 10 and 11, Pelargonium can grow as true perennials and flower year-round. For gardeners in cooler zones, the season is limited only by the temperature drops that signal the end of the year.
Optimal Timing for Planting
Timing the outdoor placement is dependent on local weather patterns. Pelargonium should not be moved outside until all danger of nighttime frost has passed. Even minor freezing temperatures can damage or kill the plant, which is why a safe planting time is often cited as mid-to-late May in many northern regions.
A more reliable indicator than the calendar is the nighttime air temperature, which should consistently remain above 55°F before planting. If purchasing plants early, they must be kept indoors or in a protected, warm environment. Before being planted, the young plants should be gradually acclimated to outdoor conditions over a two-week period, a process known as hardening off.
Extending the Active Season
To maintain prolific flowering throughout the warmer months, routine care must be implemented. The most effective way to encourage new flower production is by regularly removing spent blooms through deadheading. This redirects the plant’s energy away from seed formation and back into the creation of new flowers, extending the active season.
Proper watering is necessary for continuous growth and bloom, as these plants are semi-succulent and susceptible to root rot if overwatered. Gardeners should only water thoroughly when the top one to two inches of soil has become dry to the touch. Consistent feeding is also necessary, and a balanced, water-soluble liquid fertilizer should be applied every two to four weeks during the growing season.
Managing Geraniums During Winter
When the first hard frost approaches, the active season ends, but gardeners have options beyond treating the plants as annuals. In zones colder than 10, the most straightforward approach is to bring potted plants indoors before the first frost and maintain them as houseplants in a bright, cool location. These overwintered plants should be trimmed back and given reduced water, entering a semi-dormant state.
Alternatively, stem cuttings can be taken from healthy parent plants in late summer, rooted, and kept on a sunny windowsill over winter. A third method involves storing the entire plant in a dormant state by digging it up, removing the soil from the roots, and hanging the bare-root plant upside down in a dark, cool, frost-free location (35 to 50°F). Regardless of the method, the plants are protected until they can be moved back outside the following spring.