Agastache, commonly known as Hyssop or Hummingbird Mint, is a fragrant perennial prized for its long flowering season and strong appeal to hummingbirds, bees, and butterflies. Expanding a collection of this hardy plant is straightforward, achievable through seeds or by creating clones using cuttings or division. These methods allow gardeners to increase their plants with minimal effort.
Starting Agastache from Seed
Agastache seeds often require cold stratification to break dormancy and initiate germination, mimicking natural winter conditions. This cold, moist treatment can be achieved by sowing seeds outdoors in the fall or by artificially exposing them to temperatures near 40°F in the refrigerator for three to four weeks. When starting seeds indoors four to six weeks before the last expected frost, use a light, well-draining seed-starting mix. Press seeds gently onto the surface and leave them uncovered or with a thin layer of fine vermiculite, as light is often required for sprouting. Maintaining 59°F to 68°F encourages germination, and seedlings are ready for transplanting once they reach about four inches in height.
Vegetative Propagation using Stem Cuttings
Propagating Agastache through stem cuttings is the most reliable way to create genetically identical clones, ensuring the new plant retains the parent’s exact color and growth habit. The best time to take cuttings is from late spring to early summer, selecting four to six-inch sections of non-flowering, semi-hardwood stem. Prepare each cutting by removing all leaves from the bottom two nodes and lightly scraping the stem base to expose the cambium layer. Dipping the prepared end into a powdered or gel rooting hormone increases the probability of successful root development.
Insert cuttings into a sterile, porous medium, such as a mix of perlite and sand, ensuring at least one node is fully buried. A high-humidity environment is necessary to prevent desiccation, which can be created by covering the pot with a plastic dome or clear plastic bag to form a mini-greenhouse. Place the container in indirect light and maintain a temperature around 70°F. Roots typically form within two to three weeks. Once new leaves emerge and a gentle tug on the stem meets resistance, the cutting is rooted and can be gradually acclimated to lower humidity.
Multiplying Plants Through Division
Dividing mature Agastache clumps is a fast and effective method for propagation and for rejuvenating older plants that have become sparse in the center. Perennial varieties benefit from division every three to five years to maintain vigor and robust flowering. The ideal time is in early spring just as new growth emerges, or in early fall, at least six weeks before the ground freezes.
To divide the plant, carefully dig up the entire clump, minimizing damage to the root system. The large root ball can be separated into smaller sections using a sharp spade, garden knife, or two garden forks placed back-to-back. Each resulting division must contain a healthy portion of the root system and at least one visible growth bud, often referred to as an “eye.” These smaller clumps should be replanted immediately into their new location.
Post-Propagation Care and Transplanting
New plants require specific care to transition successfully into the garden environment. Seedlings and rooted cuttings grown indoors must undergo a “hardening off” period to gradually acclimate them to direct sun, wind, and outdoor temperatures. This involves moving the young plants outdoors for increasing periods over one to two weeks before final planting.
Agastache thrives in full sun and lean, well-drained soil, as excessive moisture, particularly in winter, can cause root rot. When transplanting, set the new plants at the same soil level they were growing in previously, and gently firm the soil around the root ball. Immediately after transplanting, deep watering is necessary to settle the soil and reduce transplant shock.