Purple Giant Hyssop is a perennial wildflower native to Eastern North America. Scientifically known as Agastache scrophulariifolia, it can grow up to 6′ tall in optimum conditions. Blooming densely flowered white to lavender spikes in late summer for 3-6 weeks, it attracts a variety of pollinators including bees and even the occasional hummingbird.
In this article:
- What is Purple Giant Hyssop
- What are the benefits of Purple Giant Hyssop
- How to grow and care for Purple Giant Hyssop
- Identification / Characteristics
- What Wildlife, Pests, and Diseases effect Purple Giant Hyssop
- Where to buy Purple Giant Hyssop
- Uses of Purple Giant Hyssop
- Final thoughts
What is Purple Giant Hyssop
A herbaceous perennial, Purple Giant Hyssop is a long blooming late season wildflower that attracts numerous pollinators including up to 14 species of butterfly. Growing well in full sun or partial shade, it is adaptable in the garden as long as the soil drains well. A good choice for the back or North side of a flower bed, it can reach 6′ tall in preferred conditions. 
Like it’s more popular cousin, Anise Hyssop, it has bitter tasting foliage that keeps deer and rabbits away. However, it still was used medicinally by Native Americans and essential oils are obtained from the flowers.
Purple Giant Hyssop Facts
- The Native Range of Purple Giant Hyssop is basically in between the Missouri river and the Atlantic ocean. So, the Eastern border of the Dakotas/Nebraska, then straight East to New England.
- Purple Giant Hyssop attracts over 14 species of butterflies, moths, and bees, including the endangered rusty patch bumble bee. It even will attract hummingbirds. 
- Songbirds will eat the seeds in early fall as they become available
- The large size of Purple Giant Hyssop makes it a great choice for a border garden, or along a fence
- Historically, Purple Giant Hyssop was used medicinally by Native Americans
- Similar to its cousin, Anise Hyssop, leaves of Purple Giant Hyssop contain essential oils that are quite fragrant
- Purple Giant Hyssop is listed as threatened or endangered in 4 states.
Native Range of Purple Giant Hyssop
Native to the Northern half of Eastern North America, Purple Giant Hyssop is hardy from zone 3 to 8.
Purple Giant Hyssop Reference Table
|Scientific Name||Agastache scrophulariifolia|
|Common Name(s)||Purple Giant Hyssop, Giant Hyssop, Prairie Hyssop|
|Native Range, USDA Zone||Eastern North America. USDA Hardiness Zones 3-8|
|Bloom Duration, Color||3-6 weeks, White to lavender|
|Height||2-6′ (30-180 cm)|
|Spacing / Spread||1.5-3′ (45-90 cm)|
|Light Requirements||Full sun to partial shade|
|Soil Types||Sandy loam to clay loam|
|Moisture||Slightly moist to slightly dry, well drained|
|Fauna Associations / Larval Hosts||Bees, syrphid flies|
What are the Benefits of Purple Giant Hyssop
Long bloom period
With a blooming period of 3-6 weeks, Purple Giant Hyssop will look great in your garden much longer than most perennials.
Purple Giant Hyssop is able to grow in a variety of light conditions and almost any soil, provided it drains. This makes it highly versatile in the garden or yard.
By attracting lots of bees and over a dozen species of butterflies, Purple Giant Hyssop will bring in pollinators to your garden and yard. If you have 3 or more of this specimen clustered, you will likely be able to just hang out near it and observe all the activity.
Grow and Care for Purple Giant Hyssop
For sunlight, Purple Giant Hyssop will grow largest in full sun, which is at least 6 hours per day. In partial shade it is a bit shorter, reaching 3-4 feet (in my experience).
For soil Purple Giant Hyssop is quite adaptable in that it can grow in a wide variety of soil textures. Sandy loam, loam, silt, and clay-loam are all perfectly fine for a growing medium provided they drain well.
Purple Giant Hyssop will tolerate slightly moist to slightly dry conditions in the garden. But make sure the soil drains well, as it can suffer from root rot.
Purple Giant Hyssop may require seed-head removal in formal flower beds to prevent unwanted self-seeding.
As a native plant Purple Giant Hyssop will not require supplemental fertilizer.
How to Grow Purple Giant Hyssop from Seed
Like other hyssops, Purple Giant Hyssop seed requires a period of cold moist stratification of sixty days and exposure to sunlight to germinate. But if you Winter Sow the seed and plant it on top of the soil, you should have no trouble achieving a high germination rate.
Process to germinate Purple Giant Hyssop seed
- Fill a suitable container with moist potting soil. Since the seed is tiny, try to make sure there are no twigs or debris on the surface.
- Press Purple Giant Hyssop seed into the surface of the soil, taking care not to bury it. It requires exposure to sunlight to help break dormancy.
- Set the container in a location that will receive morning sun and afternoon shade.
- Germination should begin once temperatures warm up in Spring. For stratified seed planted when temps are warm, expect germination within 2-3 weeks.
If transplanted to it’s final location early enough, it may be possible to obtain a couple blooms on a first year plant. But this would likely be rare, but you should expect blooms by the second year, and a full-sized plant in the 3rd year.
Identification and Characteristics of Purple Giant Hyssop
The overall plant is quite large, typically growing upwards of 5-6′ in optimum conditions.
Stalks will be medium green in color, and strong/erect. Being a member of the mint family, the cross-section of a stem will be square or diamond shaped, having four angled corners. There may be branching in the upper third of the plant. 
Like it’s cousin Anise Hyssop, the leaves should smell like black licorice when crushed or torn.
At the end the stalk will be spikes or white to lavender-white flowers that are 1-6″ long (2.5-15 cm). The spikes are densely packed with flowers that are quite tiny, 1/4″ (6mm) long by 1/16″-1/8″ diameter (1.5-3mm). 
Individual flowers will open and close on their own over a six week to two month period beginning in Summer and lasting until late Summer / Fall. This long period of available nectar makes the plant valuable to pollinators.
About four to six weeks after blooming the spikes will turn brown and dry out. At this time you can collect the seed heads. Store seed heads in a brown paper bag in a cool dry place for about a week, then crush the seed head to have the tiny seeds fall out. Fully dry seeds can be stored in a cool dry place in a baggy or envelop.
The root system of Purple Giant Hyssop is fibrous roots with tiny to short rhizome stems.
Wildlife, Pests, and Diseases associated with Purple Giant Hyssop
Numerous species of long tongued bees and butterflies have been documented visiting Purple Giant Hyssop. The numerous blooms and duration of blooming period make this plant very attractive to pollinators.  Other research has found it to be one of the more popular plants with rare or endangered pollinators. 
Due to the large number of pollinators attracted, Purple Giant Hyssop will also attract predatory insects such as wasps and Robber Flies. These insects may pray on our beloved pollinators, but they also prey on insects that are pests in the vegetable garden.
There are no real pests that damage the appearance of Purple Giant Hyssop. Drought can manifest in the form of leaf damage or ugliness, but not much in the way of disease.
Deer and Rabbits
Due to the fragrant and bitter foliage, deer and rabbits leave Purple Giant Hyssop alone.
Where you can buy Purple Giant Hyssop
Purple Giant Hyssop is not typically sold in big-box nurseries But it can be purchased at specialty nurseries that deal in Native Plants. You can find native plant nurseries near you on our interactive map.
Where to buy seeds
We have ordered a variety of native flower seeds from Everwilde Farms, which you can order right from Amazon through our link on our RECOMMENDED PRODUCTS PAGE. (We may earn a small commission when you purchase through our links, at no cost to you. This helps support our website.)
Uses of Purple Giant Hyssop
Purple Giant Hyssop can do well in a border garden, meadow, micro-prairie, in upland woods. It can be used as a taller plant towards the back, or North side of a flower bed (so it doesn’t shade out other plants).
As Purple Giant Hyssop is quite adaptable, it can grow well with most plants that like well-draining soil (which is most). But for some suggestions of plants that bloom concurrently with Purple Giant Hyssop:
- Wild Bergamot
- Showy Goldenrod
- Black Eyed Susan / Rudbeckia
- Gray Headed Coneflower
- False Sunflower
- Echinacea purpurea
- Joe Pye Weed
- New England Aster
The Native American Mewskwaki Tribe used Purple Giant Hyssop created an infusion using the root. They used this as a diuretic.[na] The leaves also contain essential oils that are used aromatically. 
For a tall long-blooming pollinator magnet, Purple Giant Hyssop is a great choice. The foliage generally looks great, the flowers are attractive, and the insect/pollinator activity is interesting to look at. When you need a tall plant, you should consider Purple Giant Hyssop.
 – Sheahan, C.M. 2012. Fact sheet for purple giant hyssop
(Agastache scrophulariifolia). USDA-Natural Resources
Conservation Service, Cape May Plant Materials Center.
Cape May, NJ. 08210. https://plants.usda.gov/DocumentLibrary/factsheet/pdf/fs_agsc.pdf Retrieved 18DEC2022
 – Purple Giant Hyssop. USDA NRCS. Accessed 18DEC2022.
 – MacLEOD, MOLLY KATHERINE. How do species abundance distributions influence plant–pollinator networks?. Rutgers The State University of New Jersey-New Brunswick, 2016.
 – Katherine Odanaka Josh Hall Sabine Nooten Sandra Rehan. Wild Bees of New England, University of New Hampshire Department of Biological Sciences Rehan Lab, 2018, pp121.
 – Vârban, Rodica, et al. “Phenological assessment for agronomic suitability of some Agastache species based on standardized BBCH Scale.” Agronomy 11.11 (2021): 2280.
 – Robertson, Charles. “Flowers and insects; lists of visitors of four hundred and fifty-three flowers.” (1928).
 – North American Ethnobotany Database. Agastache scrophulariifolia. Accessed 18DEC2022.
 – Georges C. Lognay, M. Verscheure, B. Steyer, Michel Marlier, Eric Haubruge & Marc Knaepen (2002) Volatile Constituents of Agastache scrophulariaefolia (Willd.) Kurtze. Leaves, Journal of Essential Oil Research, 14:1, 42-43, DOI: 10.1080/10412905.2002.9699757
The Black Cherry is a deciduous hardwood tree native to North America. Scientifically known as Prunus serotina, it will grow 80' tall in full sun and well draining soil. Blooming numerous white...
Aromatic Aster is a herbaceous perennial native to North America. Scientifically known as Symphyotrichum oblongifolium, it grows 2-3' tall by 2-3' wide in full sun and dry to medium-moist soil. One...