Glycyrrhiza glabra is a perennial herb valued for its subterranean components, the roots and runners that yield the characteristic sweet flavor of licorice. This sweetness comes from the compound glycyrrhizin, which is significantly sweeter than table sugar. Cultivating this plant requires patience, as the root mass takes several years to develop the required potency for harvest. Successful growth relies on understanding and replicating the specific environmental conditions that encourage deep, vigorous root development. This guide provides the steps necessary for growing true licorice, from preparing the soil to the final harvest and processing of the root.
Establishing the Optimal Growing Environment
Licorice thrives best in regions that mimic its native Mediterranean climate, generally USDA Hardiness Zones 7 through 9 or 10. The plant requires long, hot summers to fuel the necessary energy storage in its roots and can tolerate moderate winter temperatures, surviving mild frosts down to approximately 5°F when well-established. Full sun exposure is essential for robust growth, although plants in the hottest climates may tolerate a small amount of afternoon shade.
The soil composition is perhaps the single most important factor for licorice cultivation. It requires a deep, rich, and well-draining substrate, often described as sandy or silty loam. Licorice develops a deep taproot that can reach several feet, so the soil must be loose and free of stones to allow for vertical growth.
An ideal soil pH is slightly alkaline, ranging between 6.5 and 8.0. Poor drainage will quickly lead to root rot. Amending heavy clay soil with generous amounts of sand, compost, or perlite is necessary to prevent waterlogging and encourage deep root penetration.
Propagation and Initial Planting Techniques
The most reliable and common method to start licorice is using root or rhizome cuttings. These cuttings ensure the new plant is genetically identical to the parent, preserving desirable traits. Root cuttings should be planted in the early spring, positioned horizontally about one to two inches below the soil surface.
Starting licorice from seed is possible but involves a longer and more challenging process. The seeds possess a hard outer shell, requiring scarification, such as gently nicking the seed coat or soaking them in warm water for 24 hours to improve germination rates. Germination can be slow and sporadic, taking several weeks.
Seedlings or established root cuttings should be transplanted once the danger of the last frost has passed. Due to the plant’s aggressive and far-reaching root system, plants must be spaced at least 18 to 30 inches apart to allow for proper development. When planting, dig a hole that is deep enough to accommodate the roots vertically and backfill with the prepared, well-draining soil mix.
Ongoing Maintenance and Controlling Spread
Once established, licorice is a low-maintenance plant, though it does require consistent moisture. Deep, regular watering is preferable to shallow watering, as this encourages the development of the deep taproot. The plant is drought-tolerant once mature, but the highest quality roots are produced when the soil is kept evenly moist, never saturated.
As a member of the legume family, Glycyrrhiza glabra fixes nitrogen into the soil. Over-fertilizing, particularly with nitrogen, can promote excessive leaf growth at the expense of root development. Fungal issues like powdery mildew can occur in areas with poor air circulation, and root rot remains a risk in overly wet conditions.
The most demanding aspect of care is managing the plant’s aggressive spread. These lateral roots can travel up to 26 feet from the mother plant, quickly turning the licorice patch into an invasive problem. To contain this spread, gardeners should install a rigid root barrier, buried vertically around the planting area. The barrier should extend at least 18 inches deep and protrude above the soil line to prevent runners from growing over the top.
Harvesting and Processing the Licorice Root
The roots are not ready for harvest until the plant is mature, typically three to five years after planting. Harvesting before this time will yield roots that lack the desired concentration of glycyrrhizin. The best time for harvest is in the late fall or early spring, after the above-ground foliage has died back, which is when the plant has concentrated its energy and starches into the root system.
Harvesting involves carefully excavating the deep and often extensive root network. A broad fork or long-handled spade is needed to gently lift the root crown. Gardeners can choose to remove the entire plant or practice selective harvesting by digging up the lateral runners and leaving the main taproot intact, allowing the plant to regenerate for future harvests.
Once removed, the roots must be thoroughly cleaned of soil, cut into smaller pieces, and then dried. Drying reduces the moisture content to a level suitable for preservation. This process can be achieved by air-drying the roots in a warm, shaded, well-ventilated area for several weeks, or by using a food dehydrator set to a low temperature to avoid damaging the active compounds.