Yarrow, or Achillea millefolium, is a perennial herb valued for its unique properties. It has been used historically for medicinal and ornamental purposes. Properly harvesting yarrow at its peak concentration ensures that the chemical compounds responsible for its distinct aromatic and biological qualities are preserved. The timing of the harvest is directly linked to the concentration of volatile oils and tannins within different parts of the plant. Understanding when and how to collect each part is necessary to maximize the herb’s full potential.
Identifying Peak Potency: Timing the Flower Harvest
The maximum potency of the flowering tops is reached when the essential oil concentration is highest, generally in mid-to-late summer. The precise timing depends on local climate, so the most important indicator is the stage of the flower head itself, not the calendar date.
The ideal moment to harvest is when the flower clusters are fully open and appear bright white or pink, before the small ray flowers begin to show signs of browning or yellowing. Once the flower heads have passed their peak and started to set seed, the concentration of aromatic oils declines.
Harvesting on a dry, sunny day is recommended to ensure the plant material is free of excess moisture. It is best to collect yarrow in the late morning, after the morning dew has completely evaporated. This timing allows the sun to dry the surface moisture while ensuring the essential oils have not yet dissipated due to intense heat. Collecting dry flowers prevents mold and mildew from developing during the curing process.
Harvesting Techniques for Leaves and Roots
The leaves of yarrow are highest in compounds like tannins earlier in the growing season, before the plant allocates energy to flowering. They can be harvested when young in the spring, or just prior to the flower heads opening. When collecting leaves, select healthy, lower foliage and leave enough on the stem to ensure the plant can continue to photosynthesize.
When harvesting the aerial parts—the flowers, leaves, and stems—use clean, sharp pruning shears to make a precise cut. Cut the stem several inches above the ground, leaving a base of two to three inches of foliage. This technique ensures the plant has enough residual growth to regenerate and possibly produce a second flush of flowers later in the season.
The roots are best harvested when the plant is dormant and has retracted its energy underground. This usually falls in the autumn after the plant tops have died back or in early spring before new growth emerges. Harvesting during dormancy ensures the highest concentration of underground compounds, such as alkaloids.
To harvest the root, the entire plant must be carefully dug up, minimizing damage to the rhizomes. Once removed, the roots must be thoroughly washed to remove all dirt and debris. They are often preserved fresh in alcohol for tinctures or dried for later use.
Curing and Storage Methods
Proper curing is necessary to prevent spoilage and maintain the chemical integrity of the harvested yarrow. The most common and effective method is air drying the plant material in small, loose bundles. These bundles should be secured at the stem end and hung upside down in a dark, dry, and well-ventilated location.
Good airflow is necessary to quickly remove moisture, which significantly reduces the risk of mold formation. The drying area should be kept cool, and direct sunlight must be avoided, as ultraviolet light can degrade the plant’s sensitive essential oils and reduce potency. Alternatively, flower heads and leaves can be spread in a single layer on screens or racks for horizontal drying.
The yarrow is considered fully cured and ready for storage when the plant material is completely brittle. A simple test is to bend a stem: if it snaps cleanly rather than bending, the drying process is complete. Leaves should crumble easily between the fingers once they are fully dried.
Once dried, the plant material should be stripped from the stems and stored whole or coarsely cut. Long-term storage requires airtight containers, such as sealed glass jars, to prevent any reabsorption of humidity from the air. These containers should then be kept in a cool, dark location away from heat sources and light to ensure the potency of the preserved herb is maintained.