Yarrow (Achillea millefolium) is a garden favorite, known for its fern-like foliage and flat-topped flower clusters. This hardy, drought-tolerant perennial is easy to establish, provides reliable color, and attracts beneficial pollinators. Successfully cultivating yarrow from seed requires attention to specific timing and soil conditions to ensure young plants develop a strong structure.
Timing and Site Preparation
Planting yarrow seeds depends on your local climate, offering options for starting them indoors or sowing them directly into the soil. To gain an early start, gardeners typically start seeds indoors six to eight weeks before the final expected spring frost date. Direct sowing can be done in the garden during early spring or in the fall, allowing establishment before summer heat or winter cold.
The choice of site is important for preventing the leggy, weak growth that can plague yarrow. Select a location that receives full sun exposure throughout the day, as plants grown in partial shade often develop elongated, spindly stems. Yarrow thrives best in well-drained, average-to-poor soil, tolerating conditions that many other perennials cannot.
Avoid amending the planting area with excessive organic matter or fertilizers. Overly rich or moist soil can lead to rapid, floppy growth that compromises the plant’s sturdiness. Standard Achillea millefolium seeds typically germinate successfully without cold stratification, though some specialized varieties may benefit. Preparing a lean environment encourages the plant to develop a strong root system rather than excessive foliage.
Step-by-Step Sowing Technique
Yarrow seeds are small and require specific conditions to break dormancy, most notably a requirement for light to trigger germination. When planting in seed trays or flats indoors, fill the containers with a fine-textured, moistened seed-starting mix before scattering the tiny seeds across the surface. It is important to surface-sow the seeds and avoid burying them, as light contact is necessary for the biochemical processes that initiate sprouting.
You can gently press the seeds onto the soil surface to ensure good contact, or you may cover them with a very thin, light layer of vermiculite, which helps retain moisture without blocking light. Maintain consistent moisture in the trays by misting or bottom-watering, taking care not to wash the seeds away. Covering the trays with a clear plastic dome or lid helps to maintain the high humidity levels necessary for successful germination.
For optimal results, maintain a consistent temperature range of approximately 65–70°F (18–22°C) around the seed trays. Under these conditions, the first signs of germination should appear within 10 to 21 days. If you are direct sowing outdoors, broadcast the seeds sparsely over the prepared soil, lightly press them in, and keep the area consistently moist until the seedlings emerge.
Post-Germination Care and Establishment
Once the seedlings have developed their second set of leaves, known as true leaves, it is time to thin the plants grown indoors to prevent overcrowding. Use small scissors to snip the weaker seedlings at the soil line, leaving the strongest plants spaced about one to two inches apart. This thinning process ensures that the remaining seedlings have adequate airflow, light, and nutrients to develop robust stems and roots.
Continue to provide consistent moisture to the young yarrow plants, keeping the soil damp but never waterlogged, which prevents damping-off disease. Before transplanting the indoor-grown seedlings, they must undergo “hardening off.” This process involves gradually acclimating the plants to outdoor conditions, including direct sunlight and wind, over seven to ten days.
Begin by placing the seedlings outdoors in a sheltered, shaded spot for a few hours each day, slowly increasing the duration and exposure to full sun over the week. After the danger of frost has passed, the hardened-off seedlings can be transplanted into the garden. Dig individual holes deep enough for the root ball and space the young plants widely, setting them about one to two feet apart. This generous spacing helps manage yarrow’s naturally spreading tendency via rhizomes.