The Perennial Matchmaker

The variety of colors you can find among the agastaches (Agastache) offers exciting possibilities for both bold and subtle combinations. As a group, agastaches share several characteristics, including spiky bloom clusters and a months-long flowering period.

The agastaches with purple-blue (or sometimes white) flowers are commonly referred to as anise hyssops. A. foeniculum is native to much of northern North America; A. rugosa, sometimes called Korean mint, is native to Asia. There are also hybrids, such as ‘Black Adder’ and ‘Blue Fortune’. Anise hyssops are typically hardy in Zones 4 to 9, though some newer selections are less cold-tolerant. Their heights can vary dramatically depending on the growing conditions and the ages of the plants: Though usually in the range of 3 to 4 feet tall, any of these may be as short as 2 feet or reach 5 feet or more (possibly even taller in rich soil).

Agastaches that are native to Mexico and the southwestern United States are generally referred to as hummingbird mints. Orange hummingbird mint (A. aurantiaca), reddish pink Texas hummingbird mint (A. cana), and salmon orange sunset hyssop (A. rupestris), as well as hybrids of these and other species, expand the color range with many rich shades and delicate tints of pink, orange, and yellow. They are generally 2 to 3 feet tall, with some variation either way depending on the species or selection and the growing conditions. Most of these agastaches are rated as hardy in Zones 5 or 6 to 9.

There are two aspects to the color of agastache flowers: the main one from the flower and sometimes a secondary one from the calyx (the cuplike structure at the base of each bloom).

The flowers of anise hyssops tend to be on the light lavender blue side, though some newer selections, such as ‘Black Adder’ and ‘Blue Boa’, are a somewhat richer purple, with touches of violet in their calyces. Repeat their hues with other flowering perennials in the violet-purple-blue range, such as catmints (Nepeta), perennial salvias (Salvia), and Russian sages (Perovskia), and with powder blue foliage, like that of blue fescues (Festuca) or ‘Dallas Blues’ switch grass (Panicum virgatum). The purple-blue agastaches also look wonderful with yellow, cream, or white flowers and with artemisias (Artemisia), lamb’s ears (Stachys byzantina), ‘Nora Leigh’ summer phlox (Phlox paniculata), and other plants with silver, gray, or variegated leaves. They’re very pretty with pinks and peaches, too, like those you can find in many daylily (Hemerocallis) flowers and in some foliage heucheras (Heuchera), such as ‘Berry Smoothie’, ‘Caramel’, and ‘Southern Comfort’.

Colors among the hummingbird mints range from delicate pastels, such as cream-and-pink ‘Champagne’ and pale pink ‘Cotton Candy’, to buttery ‘Sunset Yellow’, rich raspberry pink ‘Heat Wave’, and vivid orange ‘Firebird’. It’s not unusual for there to be two or three colors on one plant, because the flowers may fade or change hues as they age; the calyces are often dusky purple to pinkish, too. The pastels are particularly lovely in combinations you’ll see up close, where you can appreciate their subtle coloration. Try pairing them with flowering companions in other soft colors, including the purple-blue agastaches, and with silver, gray, blue, or peachy leaves. Purple sage (Salvia officinalis ‘Purpurascens’) and purple-leaved sedums (Sedum), such as ‘Purple Emperor’, as well as silvery purple heucheras, like ‘Blackberry Ice’, look wonderful in these sorts of combinations, especially when they echo the color of agastaches with dark calyces, such as sunset hyssop and ‘Summer Glow’.

Pastel-flowered hummingbird mints pair well with more saturated shades of the same hue, such as ‘Acapulco Salmon and Pink’ with richly colored ‘PowWow Wild Berry’ purple coneflower (Echinacea purpurea). Or use the reverse approach and combine a bright-flowered selection with a lighter version of the same hue: ‘Orange Nectar’ hummingbird mint with softer ‘Terracotta’ yarrow (Achillea), for instance. Vibrantly colored hummingbird mints are wonderful with tints and shades of yellow, coral, purple, and blue; with bright silver and deep purple foliage partners; and with the buff to tan seed heads of summer and fall grasses, such as feather reed grass (Calamagrostis × acutiflora) and fountain grasses (Pennisetum).

Agastaches are clump formers that mostly have a mounded form when established. First-year plants tend to be narrower, creating a distinctly vertical effect, especially when in flower. The foliage of the anise hyssops mostly has a medium texture, while the leaves of hummingbird mints tend to be smaller and are often quite narrow, giving them a finer appearance that contrasts well with larger, broader or strappy leaves, like those of irises and yuccas (Yucca).

The spikelike flower clusters are the most distinctive textural feature of agastaches. They’re normally dense but slender on the anise hyssops; on the hummingbird mints, they’re more open and wider, with larger individual blossoms. Both can work well for repeating the form of other spiky flowers, such as Culver’s roots (Veronicastrum) and penstemons (Penstemon). For contrast, use daisy-form flowers, like those of rudbeckias (Rudbeckia); large, rounded flowers, like those of daylilies (Hemerocallis); umbels, like those of yarrows (Achillea); and airy plumes, like those of giant fleeceflower (Persicaria polymorpha) and Russian sages. Agastaches also make fantastic co-stars for perennials with globe-like blooms, such as globe thistles (Echinops) and rattlesnake master (Eryngium yuccifolium).

Most agastaches aren’t very showy in spring, but ‘Golden Jubilee’, a selection of anise hyssop with bright yellow foliage, provides brilliant splashes of color that look beautiful with forget-me-nots (Myosotis), tulips, and other early bloomers.

The timing of the flowering season can vary quite a bit, depending on the species or hybrid, the age of the plant, and the climate. In warm regions, a late-spring to early-summer start is common; in cooler areas, blooms may not begin to open until midsummer. As you gain experience with how agastaches perform in your garden, you can fine-tune your choice of companions, but in any situation, partners that flower in mid- to late summer are a good bet, and those with colorful foliage are always dependable.

You’re likely to find that many agastaches continue flowering into fall, especially if you frequently pinch or clip off the finished spikes through summer. (That will also help to minimize the number of self-sown seedlings, which can be abundant unless you’re growing a sterile hybrid, such as ‘Black Adder’ or ‘Blue Fortune’.) Leave them on the plant after that, though, if you’d like to see the dried seed heads in winter.

If you enjoy making combinations that do more than look pretty, agastaches belong in your plant palette.

Want to attract wildlife? There’s a good reason that the southwestern species, in particular, are known as hummingbird mints: Their tubular blooms are very appealing to these intriguing creatures. Bees and butterflies also adore agastaches, especially the anise hyssops.

Enjoy having an abundance of fresh bouquets for your home? The spiky blooms of agastaches are wonderful for cutting, so consider adding them to an area where you grow other excellent cutting perennials, such as echinaceas (Echinacea), rudbeckias, and yarrows. These mint-family members have edible flowers, too, and the fragrant foliage is flavorful in tea, making them excellent additions to beds based on perennials that are both edible and ornamental.

Succeeding with Agastaches

Along with their many wonderful qualities, agastaches (Agastache) offer some challenges in perennial combinations. It’s quite common for them to live only one or two seasons and then disappear, even in areas where they should be fully cold-hardy. Sometimes this is due to the soil staying a little too moist during the winter months, which may explain why a given species or hybrid can overwinter in Zone 4 or 5 in one area and not below Zone 7 in more humid regions. In other cases, losses are seemingly by chance: Of three clumps growing in the same border, you might lose one or two or none or all. Fortunately, they’re quick growing enough that it’s worth treating them like annuals. But if you prefer to use longer-lived perennials for lower maintenance, then consider using other spiky plants instead, such as perennial salvias (Salvia).

Bloom Buddies

Marvelous Matches for Flowering Combos

Below are some compatible flowering perennials that overlap or coincide with the main mid- to late-summer bloom period for agastaches (Agastache).

Partners for anise hyssops (A. foeniculum, A. rugosum, and their hybrids) in average to moist but well-drained soil:

Bee balms (Monarda)

Crimson scabious (Knautia macedonica)

Daylilies (Hemerocallis)

Dense blazing star (Liatris spicata)

Echinaceas (Echinacea)

Fleeceflowers (Persicaria)

Heleniums (Helenium)

Joe-Pye weeds (Eupatorium)

Perennial lobelias (Lobelia)

Rattlesnake master (Eryngium yuccifolium)

Rudbeckias (Rudbeckia)

Shasta daisy (Leucanthemum × superbum)

Summer phlox (Phlox paniculata)

Threadleaf coreopsis (Coreopsis verticillata)

Tuberous-rooted Jerusalem sage (Phlomis tuberosa)

Partners for hummingbird mints (such as A. aurantiaca, A. cana, and A. rupestris) in average to dry soil:

Blanket flowers (Gaillardia)

Butterfly weed (Asclepias tuberosa)

Globe thistles (Echinops)

Jerusalem sage (Phlomis russeliana)

Lavenders (Lavandula)

Ornamental oreganos (Origanum)

Penstemons (Penstemon)

Perennial salvias (Salvia)

Russian sages (Perovskia)

Sea hollies (Eryngium)

Sedums (Sedum)

Torch lilies (Kniphofia)

Yarrows (Achillea)

Yuccas (Yucca)