Shiso (Perilla frutescens) is a fragrant herb in the mint family, widely used in East Asian culinary and traditional medicine. Recognized by its broad, often serrated leaves (available in green or purplish-red varieties), Shiso is also called Japanese Basil or Perilla. It imparts a unique flavor profile often described as a blend of mint, anise, and cinnamon. Gardeners frequently wonder about the plant’s lifespan because it often reappears season after season despite a seemingly annual life cycle.
The Official Classification
Shiso is botanically categorized as a tender perennial, meaning its natural lifespan extends beyond a single growing season. This classification applies specifically to tropical or subtropical climates (USDA hardiness zones 10 and 11) that remain frost-free throughout the year. In these ideal environments, the plant’s root system survives the mild winter without issue.
Shiso cannot tolerate temperatures consistently below 45°F (7°C), and a hard frost will kill the root structure. For the vast majority of temperate regions (zones 2 through 9), Shiso functions purely as a summer annual. It completes its entire life cycle within one year because its biological nature is overridden by local climate realities.
The Mechanism of Persistence
Even when Shiso is grown as an annual and dies back completely in the autumn, it frequently returns the following spring, leading many to mistake it for a perennial. This resurgence is not the original root system regrowing, but the result of an aggressive reproductive strategy called self-seeding. Shiso plants produce abundant, small flowers late in the growing season, which mature into viable seed heads before the first hard frost.
These seeds fall directly onto the surrounding soil surface. They often require a period of cold, known as stratification, which helps them break dormancy and reliably germinate when spring temperatures warm up. The resulting crop of new plants, often called “volunteer plants,” gives the illusion of a perennial return, ensuring a dense population of seedlings appears the next year.
Managing Shiso in the Garden
Understanding Shiso’s self-seeding habit is helpful for gardeners who want to control its spread or ensure its return.
Controlling Spread
To prevent the herb from becoming overly prolific, the most effective action is to remove the flower stalks before they mature. This practice of deadheading should begin in late summer, cutting the flowers off before they set seed. Cultivating Shiso in containers is another practical approach to limit spreading. This isolates the soil and prevents seeds from settling in the garden bed, allowing for easy disposal of the soil at the end of the season.
Overwintering the Plant
For those in marginally cold areas who want to maintain the original plant as a true perennial, move a potted plant indoors before the first frost. Placing the container in a bright, cool location over winter can preserve the root ball. This allows the plant to resume growth when returned outdoors in the spring.