Yarrow (Achillea millefolium) is a resilient perennial herb known for its delicate, fern-like foliage and flat-topped flower clusters. Propagating this plant from seed is a common practice for gardeners, but the seeds possess a natural dormancy that must be overcome for successful sprouting. Understanding the specific needs of yarrow seeds can dramatically increase the yield and vigor of your garden starts.
Understanding Cold Stratification for Yarrow
The question of whether yarrow seeds require cold stratification has a nuanced answer. Cold stratification breaks seed dormancy by exposing seeds to simulated winter conditions: a period of cold temperatures while kept moist. For yarrow, this treatment is generally not absolutely necessary to trigger germination, but rather acts as a strong promoter of success.
Native or wild varieties of Achillea millefolium possess a natural physiological dormancy. Subjecting them to a cold, moist period significantly increases the speed, rate, and uniformity of germination. Growers frequently find that two to four weeks of cold stratification yields far superior results compared to untreated seeds, which can be erratic and slow to sprout. Commercial or cultivated varieties may have a lesser need for the treatment, but adding it rarely harms and often helps the overall process.
Practical Methods for Cold Treatment
The most reliable way to provide yarrow seeds with their preferred cold period is through artificial stratification, often called moist chilling. This method mimics the natural conditions of seeds overwintering on the ground. Begin by gathering your seeds and a moisture-retaining material like a paper towel or fine, moist sand.
The chosen material should be dampened so it is moist but not dripping wet, and the seeds are then spread onto it. This assembly is placed inside a sealed plastic bag or container to retain humidity. The entire package is then moved to a household refrigerator, where the temperature falls within the ideal range of 33°F to 40°F. The seeds should remain in the refrigerator for a minimum of three to four weeks to overcome their dormancy. Check the bag periodically for excessive moisture or mold, ensuring the medium remains consistently damp.
Sowing and Germination Requirements
Once stratification is complete, or if you choose to skip the treatment, sow the seeds in a sterile, well-draining seed-starting mix. Yarrow seeds require light to germinate, so they must be sown directly on the surface of the growing medium. Press the seeds lightly into the soil surface to ensure good contact, but avoid covering them with potting mix.
A thin dusting of fine vermiculite can help retain surface moisture without blocking the necessary light. The ideal temperature range for active germination is typically between 65°F and 70°F. Maintaining this warmth, often with a heat mat, encourages sprouting within 10 to 14 days. Yarrow is best started indoors six to eight weeks before the final expected frost date, allowing the seedlings sufficient time to develop before transplanting into the garden.