Wanted: Tough plant for sunny site. Must need little or no water. Ideal candidate thrives on benign neglect and poor soil. Plays well with others. Please apply to empty space behind the salvia and santolina.
If you’ve been looking for the perfect plant for a problem spot, you’ll want to get to know agastache (ag-ah-STACK-ee). Its common name is giant hyssop, although species and cultivars are known by many names, such as hummingbird mint and licorice hyssop. Agastache is a member of the mint family, but unlike its world-conquering cousins, it is noninvasive. (It does self-seed, but it won’t take over your garden.) This plant uses few precious resources, like water and soil nutrients. And it isn’t attacked by pests—in fact, its scent repels them.
Too good to be true? Then stop reading right here, because you won’t believe the rest.
Agastache ‘Summer Fiesta’ has 28-inch-tall flower spikes that bloom from summer until frost.
How to grow
Agastache is generally hardy in Zones 4 to 10, depending on cultivar. You may be able to grow it in slightly colder zones if you plant it in a sheltered area.
That “hotter than heck” strip next to the driveway, sidewalk, or street is the best place for this plant. If you have a wall that reflects sunlight and fries everything else, you could plant some agastache right up against it. The lower-growing cultivars are great in containers, too. Masses of the taller species make an attractive ground cover, and individual plants add notes of color in a meadow.
Drought tolerance is the hallmark of agastache. Although every plant needs regular watering through at least the first season, this one needs less water from the start. In subsequent growing seasons, just turn off the hose and put your feet up. Agastache will thrive on available rainfall even in low-water areas.
Poor soil does not daunt this plant; in fact, most cultivars need sandy or coarse, fast-draining soil. Clay will kill it; fertile loam is overkill. No fertilizer, please, or this plant will become leggy and will not produce the flower-rich spikes that hummingbirds love so much.
Deadhead agastache so it’ll stay bushy and keep producing blooms.
Sunset hyssop (Agastache rupestris)
Giant hyssops are spiky and upright, but they don’t require staking and they aren’t always giants. Some of them grow in mounds only up to 2 feet tall. But many grow to between 4 feet and 5 feet, which makes them a great presence in the back of a border. If you are looking for alternatives to medium-sized shrubs, giant hyssop qualifies as a good substitute.
These plants come in many colors. Look for companions in the same shades or complementary hues.
Agastache looks great next to other spiky shapes. Lavender is a favorite companion. ‘May Night’ salvia (Salvia x sylvestris ‘May Night’, Zones 4 to 9) is another purple pal for contrast, because its especially deep color is not found in agastache cultivars. Almost any ornamental grass is perfect beside, behind, or between giant hyssops.
Small shrubs like Texas red sage (Salvia greggii, Zones 6 to 10) and Apache plume (Fallugia paradoxa, Zones 4 to 9); tall subshrubs like Caryopteris x clandonensis ‘Dark Knight’ (Zones 5 to 9); and perennials such as red hot poker (Kniphofia uvaria, Zones 5 to 10) work well with giant hyssop. They all have spiky looks that echo the shape of this plant.
Rounded shapes planted at their feet can help cover up the lower, sometimes sparser parts of giant hyssop. Try santolina (Santolina spp., Zones 6 to 11, depending on species), cranesbill geranium (Geranium sanguineum, Zones 3 to 8), or a dwarf goldenrod such as Solidago ‘Little Lemon’ (Zones 5 to 9). Any low-growing herb will also look great.
For a real contrast in shape, try a smaller agastache planted at the feet of unfussy roses like the Canadian Explorer series or any Rosa rugosa.
Agastache ‘Cotton Candy’
Relax and enjoy
Powdery mildew can be a problem with any mint, but giant hyssop seems to thwart it, perhaps because of its airiness. Pests don’t bother this plant because, frankly, it reeks. It smells like catnip to me, even though some cultivars have a lemony or licorice smell. The pungent scent lingers beneath the pleasant one.
Agastache is noninvasive, but it is a mint, which means it self-seeds freely. Either pull out seedlings when they’re small or enjoy the new plants that pop up in random places in your garden.
Don't be aghast
Agastache is most often pronounced ag-ah-STACK-ee, but you’ll hear it pronounced as ag-ah-STASH-ee, ag-AST-a-kee, and ag-AH-stah-kee. The name comes from the Greek aga, meaning highly or greatly, and stache, meaning wheatlike. Giant hyssop does greatly resemble a stalk of wheat in its upright habit, height, and sometimes size. But no matter how you pronounce agastache, be prepared for bystanders to respond, “Bless you!”
7 Awesome Agastaches
For eye-popping color that won’t fade in summer’s heat, try these agastache varieties:
‘Ava’: Raspberry and ravishing, this cultivar is a hummingbird magnet. At 4 to 5 feet tall, it’s a worthy specimen to plant all by itself. Zones 5 to 9.
A. neomexicana: This purply-pink species has airy spikes that will sparkle in your late summer garden. Also known as New Mexico hummingbird mint. Zones 5 to 10.
A. rupestris: Pink and orange haven’t been combined this prettily since the ’60s. Also known as licorice mint or sunset hyssop. Zones 5 to 10.
‘Blue Blazes’: Yellow swallowtail butterflies and other beneficial insects will love this brand-new dark-purple beauty. Grows 4½ feet tall. Zones 5 to 9.
‘Cotton Candy’: This lovely pink cultivar keeps its color even in harsh sunlight. Needs a bit more soil enrichment to help it be drought tolerant. Zones 6 to 9.
‘Summer Fiesta’: Hummingbirds will party all summer long with this nectar-rich cultivar. Spicy orange-red is a great color to perk up the dog days. Zones 6 to 10.
‘Summer Sunset’: An absolute knockout that blooms all summer. Diminutive size of 14 inches tall. Zones 6 to 10.