Wild lettuce, specifically the species Lactuca virosa and its relatives, is a biennial plant sometimes referred to as wild opium or bitter lettuce. These common names reference the bitter, milky sap it produces. The active compounds, primarily sesquiterpene lactones like lactucin and lactucopicrin, are concentrated in this white exudate. Harvesting this plant requires precise timing and proper identification to ensure maximum concentration of these compounds.
Essential Identification Before Harvesting
Correct identification of Lactuca virosa is essential before harvesting. The most distinctive feature of true wild lettuce is the milky white sap, known as lactucarium, which immediately oozes out when the stem or a leaf is broken.
The leaves also possess a defining characteristic: small, stiff prickles or hairs that run along the underside of the central midrib. This midrib hairiness distinguishes wild lettuce from many non-medicinal or toxic look-alikes, such as Sow Thistle. While some related species like Prickly Lettuce (L. serriola) have more pronounced spines, the prickles are always present. Wild lettuce typically begins as a basal rosette of leaves before sending up a tall, rigid flower stalk.
Optimal Timing Based on Plant Maturity
The potency of wild lettuce is directly linked to its life cycle. The goal is to collect the plant when it is concentrating the highest levels of the bitter lactucarium, which generally occurs just as the plant begins its reproductive phase.
The initial stage, before the plant “bolts,” is suitable for harvesting basal leaves for general use or drying. During this vegetative growth phase, the leaves are less bitter and easier to process, but the concentration of lactucarium is significantly lower than in later stages.
Maximum potency is achieved during the transition from vegetative growth to flowering, known as bolting. This is when the plant rapidly elongates a thick, upright flower stalk. The sap containing lactucin and lactucopicrin becomes highly concentrated in the stalk during this time. The ideal window is typically late spring or early summer, just as the flower stalk has fully formed and the buds are starting to appear but before the small, dandelion-like flowers have fully opened.
Harvesting Specific Plant Parts
For collecting leaves, select large, healthy leaves from the lower portion of a non-bolted or newly bolted plant. Leaves should be clipped near the base, taking care to leave the upper leaves and the main stalk intact to allow the plant to continue growing and producing seeds.
To harvest the sap, or lactucarium, the plant must be in its bolting phase. One traditional method involves scoring the stem with a sharp knife, allowing the thick, white latex to ooze out, where it can then be scraped off and collected as it dries. A more efficient method for processing large quantities is to cut the entire stalk off near the base, as the latex is distributed throughout the stem and leaves at this stage.
When harvesting the whole stalk, using gloves is advisable as the sap is sticky and can stain. For propagation, seeds can be collected in the late season once the plant has fully flowered and developed its white, fluffy seed heads. Sustainable harvesting practices dictate never removing all plants from a single area to ensure the population can regenerate in the following season.
Post-Harvest Processing and Storage
Leaves collected for tea or later extraction must be dried quickly and thoroughly to prevent mold. Air-drying in a dark, well-ventilated space is sufficient, though a food dehydrator set to a low temperature (below 100°F) can yield a superior, greener product.
The raw, milky sap collected from the scored stems or extracted from the whole plant material is traditionally processed into a concentrated resin. This process often involves reducing the material in a water and alcohol mixture over low heat, which concentrates the lactucarium into a dark, gummy paste.
For long-term storage, dried leaves should be crumbled and placed in airtight containers, stored away from light, heat, and moisture. The concentrated resin, once fully dried, should also be stored in a cool, dark environment to maintain its potency.