Yellow Giant Hyssop (Agastache nepetoides)

Difficulty: ⭐⭐☆☆☆

Seed Collection Time:

Late summer into early fall — typically September through October, once the tall flower spikes begin to dry and darken.

Signs Seeds Are Ready:

  • Flower spikes transition from pale green to tan or brown.

  • Individual tubular flowers dry and fall away, exposing small seed pods.

  • Mature seeds are tiny, dark brown to black, and fall free when the stem is tapped.

  • The seed heads feel dry and papery; stems may rattle slightly if shaken.

Seed Collection Steps:

  1. Clip the seed spikes once they are mostly dry but before heavy shattering begins.

  2. Place stems upside-down in a paper bag (or over a tarp) and let them finish drying for several days.

  3. Once fully dry, gently crush or roll the spikes to release the seeds.

  4. Sift or blow away chaff—the seeds are heavier and will remain.

  5. Allow seeds to air-dry for an additional day before storage.

Germination Tips:

Yellow Giant Hyssop seeds have physiological dormancy and benefit strongly from cold stratification.

  • Best results: sow outdoors in fall to allow natural winter stratification.

  • Seeds typically germinate the first spring after sowing.

Cold Stratification (C(30)):

  • Cold stratify for ~30 days at 35–40°F.

  • Sow seeds on the soil surface or lightly cover (they need some light to germinate).

  • Keep soil consistently moist but not waterlogged.

Additional Notes:

  • Germination is usually fast once conditions warm (10–20 days).

  • Plants prefer rich, moist, partial-shade woodland edges, but germinate well in standard nursery trays.