Can't say enough good things about agastache or anise hyssop. It's one of the most important plants in my garden. Beautiful, carefree and extremely popular with many varieties of butterflies. Its muted lavender spires make a lovely contrast to any of the brighter colored blooms like rudbeckia, heliopsis, helenium, etc.
I have experience with two cultivars of agastache. Both seem to be hardy in my zone 5a-4b garden. Blue Fortune has recently become very popular with gardeners everywhere, and with good reason. I see it locally in most garden centers. No pests, drought tolerant, licorice scented foliage, with an extended bloom period, these plants requires no care at all and butterflies are the big bonus. There are many other varieties of agastache but most are not reliably hardy in my cold winter zone.
Golden Jubilee is the only other agastache I grow. It is very similar to Blue Fortune but has red tinged, chartreuse spring foliage. In my garden, both are middle of the border plants reaching about three feet tall (can be cut back in spring to reduce height). Golden Jubilee can be started from seed.
On my July 26 post I showed a photo of Blue Fortune with about 50 Clouded Sulfur butterflies nectaring on the blooms. Agastache blooms from late June through July and into August.
Agastache prefers well drained soil but it does not seem to be bothered by my heavy clay even during some very wet springs and summers we have had in the past. It is perfect for hills and slopes and raised beds that drain too quickly for many plants.