Yarrow (Achillea millefolium) is a common perennial herb recognized for its historical uses in traditional remedies. This plant is valued for its volatile oils and beneficial compounds, which contribute to its distinctive aroma and properties. Successfully harvesting yarrow requires specific timing and careful technique to ensure the maximum concentration of these components. This guide provides steps for gathering and preserving the herb for optimal potency.
Identifying the Optimal Harvest Time
The potency of yarrow is directly related to the concentration of its volatile oils, which shift throughout the plant’s life cycle. Harvesting should occur during the flowering period, typically spanning late spring through summer. The ideal window for cutting the plant is when the flat-topped clusters of flowers (corymbs) are fully open but have not yet begun to fade or turn brown at the edges.
Late morning is the preferred time for collection, as the time of day influences the chemical makeup of the harvest. This timing ensures that morning dew has completely evaporated from the foliage, preventing excess moisture that could lead to mold during drying. Harvesting after the dew dries but before the intense heat of midday helps maximize the volatile oil content, which is most concentrated in the fresh aerial parts.
Step-by-Step Collection Techniques
When gathering yarrow, focus on the aerial parts—the flowers, leaves, and upper stems—as these contain the highest levels of beneficial compounds. While the flowers are particularly rich in aromatic oils, the upper leaves and stems also contribute valuable components. Using sharp, clean tools like scissors or pruning shears ensures a quick and non-damaging cut to the plant, which minimizes plant stress.
To promote the health of the patch and encourage future harvests, cut the stems a few inches above the ground, leaving the basal rosette of leaves untouched. This practice allows the plant to recover quickly, often producing a second flush of blooms later in the season. For sustainable harvesting, only take about one-third of the available stems from any single stand of plants to ensure the patch remains healthy and reproduces for the following year.
Drying and Storing the Harvest
After collection, the plant material must be prepared immediately to prevent the degradation of its sensitive volatile oils. Avoid washing the harvested yarrow, as introducing excess water increases the risk of mold and can diminish the potency of the herb. Instead, gently shake the cuttings outdoors to remove any loose dirt, dust, or small insects before bringing them inside for processing.
The most effective method for preservation is air-drying, which should take place in a cool, dark, and well-ventilated space, such as an attic or a dedicated drying room. Gather the stems into small, loose bundles and hang them upside down, which helps maintain the shape of the flowers and encourages even drying. Alternatively, the flowers and leaves can be spread in a single layer on fine-mesh drying screens or trays, ensuring no pieces overlap to allow for proper airflow.
The drying process is complete when the stems snap easily and the leaves are fully brittle and crumbly, which can take between one and three weeks depending on the humidity. Once dried, strip the leaves and flowers from the stems and store them in airtight containers, such as dark glass jars. Keeping the sealed containers in a cool, dark location, away from direct light and heat, is necessary to preserve the potency of the oils for up to one year.