Hyssop (Agastache sp.)
Agastache foeniculum

Zone: 5 to 9

Soil: Sand to clay

Light: Full sun to part sun

Bloom colour: Blue, Yellow, Purple

Bloom period: mid-summer to frost

Height: Up to 96 inches

Moisture: Average

Attracts: Bees and butterflies and hummingbirds.

Notes: Agastache foeniculum (Anise Hyssop) is native prairie plant that is also found in N.W. Ontario. Agastache nepetoides (Yellow Giant Hyssop) and Agastache scrophulariifolia (Purple Giant Hyssop) are native across the Eastern states and provinces although they can be locally quite rare. In southern Ontario, A.nepetoides is the most common species.

Agastache foeniculum and Agastache scrophulariifolia are similar in appearance. However, Anise Hyssop only grows to about five feet tall while the other two native species grow up to 8 feet. Anise Hyssop has leaves that are strongly scented with Anise and each flower has a calyx that is the same colour as the flower itself. Agastache scrophularia has leaves with some Anise scent, but each flower has a green calyx. The flowerheads are the most reliable way to identify the two species.

Agastache foeniculum
Agastache foeniculum
Agastache 'Blue Fortune'

In natural settings, Agastache foeniculum grows in open spaces and requires the most light. Agastache nepetoides is the most shade tolerant, flowering with less than two hours of sunshine each day. All three species are somewhat drought tolerant, but may show signs of heat stress when subjected to direct sun during the middle of the day. The tips of each shoot droop, but can recover nicely.

Anise Hyssop is by far the most widely available species in garden centres and you might also be able to find it being sold as a kitchen herb. Agastache 'Blue Fortune' is a sterile hybrid that could be an acceptable substitute for Anise hyssop because it looks quite similar, attracts loads of pollinators and will not spread to other places. Unlike many other hybrids, it is also cold hardy.

Anise hyssop is the most attractive of the three native species as a garden plant because the blue calyxes make the flowerheads colourful even when there are few flowers present. If you have shade, Yellow and Purple Giant Hyssops are still one of the best choices to attract insects in mid-summer and due to their size should be planted at the back of the border. Purple Giant Hyssop has a long flowering season and is also popular with hummingbirds. Yellow Giant Hyssop tends not to branch too much so it is necessary to plant several specimens 18 inches apart. Purple Giant Hyssop is large enough to be planted as a single specimen and works well as a companion to Cup Plant. I recommend Purple Giant Hyssop as a native alternative to Buddleia.

All other Agastache have trouble surviving winters in Ontario. There are many hybrids which should be treated as annuals. They are typically in the red to purple range and can be used to attract hummingbirds. The corollae in the three native species are short and the nectar is available to a wide range of pollinators including hummingbirds. As an example, the hybrid Agastache 'Apricot Sunrise' is shown here.


Agastache nepetoides and Agastache scrophularifolia
Agastache scrophulariifolia (Purple Giant Hyssop) and Agastache neptoides (Yellow Giant Hyssop).
Agastache scrophularia
Agastache scrophularia
Agastache Apricot
Agastache 'Apricot Sunrise'
Agastache with a Monarch butterfly
A monarch butterfly on Agastache scrophularia