Hyssop (Agastache) is a sturdy perennial that, once established, will thrive in poor soil, freezing weather and drought. At maturity, hyssop will measure 18 to 24 inches tall. The wiry stems will be covered with tiny, pungent green leaves and spiky purple blooms. Divide hyssop when it begins to outgrow its boundaries. Replant the hyssop in another area in your garden, or share the divided hyssop with friends.
Divide hyssop in early spring when new growth is just beginning to emerge. The plant will be small, and will have plenty of stored up energy to get the division off to a good start. Divide hyssop in the morning on a cool, overcast day so the roots will have time to settle in their new home before the heat of the day.
Use a shovel or a garden fork to dig a clump of hyssop. Dig an entire clump, or if the clump is large, use the point of a shovel to separate a smaller clump, leaving the main hyssop plant intact.
Divide the hyssop into smaller sections, teasing the roots carefully apart with your fingers. Be sure each division is large enough to have several healthy roots.
Plant the hyssop divisions in a sunny, well-drained spot in your garden. Use a trowel to dig a hole large enough to accommodate the hyssop's root system. Plant the hyssop in the hole and tamp the soil down gently around the roots.
Water the hyssop immediately after planting and keep the soil moist until you notice new growth, which indicates that the hyssop has taken root. After this time, water the hyssop during warm, dry weather, but don't over-water. Hyssop won't tolerate soggy soil.