How to Grow Purple Giant Hyssop

This tall plant from the herb family will attract pollinators to your garden

Purple giant hyssop flower spikes with small purple petals in sunlight

The Spruce / Evgeniya Vlasova

Purple Giant Hyssop (also known as Prairie Hyssop) is a tall-growing, perennial plant from the herb family. The fragrant flowers are known to attract bees and other pollinators readily, and its height means it's often selected to grow up against fencing or in borders.

Growing up to six feet tall, this is a late flowering plant with pale purple or pink blooms that form on several spikes at the top of the stem. The leaf stems are covered in short, white hairs. This plant does well in a sandy, loamy, moist soil with limited competition around it, and it tolerates a part or full sun position.

Although it's native to North America and Eastern Asia, because of habitat destruction and competition from non-native species, it's now regarded as being rare in the wild.

Botanical Name Agastache scrophulariifolia
Common Name Prairie Hyssop, Giant Hyssop
Plant Type Perennial herb
Mature Size Up to 6 foot
Sun Exposure Full Sun/Part Sun
Soil Type A moist, loamy or sandy soil
Soil pH 5.5 to 7.5
Bloom Time Late Summer to Late Fall
Flower Color Pale purple or, less commonly, pale pink
Hardiness Zones 4 to 8
Native Area Found in rich woodland and meadows in North America and Eastern Asia

How to Grow Purple Giant Hyssop

Purple Giant Hyssop is an easy perennial to grow from seeds, although it doesn't usually bloom until the second year of growth. Deadheading flowers past their best will help to prolong its blooming period.

It grows best in moist, sandy soil with at least partial sun. It doesn't do well with a lot of competition, so don't plant it in areas with lots of other species already present. This plant can grow very tall, so make sure you position in a spot where this won't be a problem.

Purple giant hyssop plants with purple flowers on tall spikes and foliage

The Spruce / Evgeniya Vlasova

Purple giant hyssop plant spikes with small green foliage in sunlight closeup

The Spruce / Evgeniya Vlasova

Purple giant hyssop plant spikes with small purple flowers on top closeup

The Spruce / Evgeniya Vlasova


Purple Giant Hyssop does well in full sun or partially shaded areas. It's often found in woodland areas where the light will be dappled.


It can cope with a variety of soils, but it prefers a well-drained, recently disturbed sandy or loamy type. If the soil is too rich, the blooms won't reach their best potential.


Purple Giant Hyssop does well with persistently moist or semi-moist soil when growing. Once the plant reaches full maturity, though, it's more drought-tolerant, and it won't need to be watered as often.

Temperature and Humidity

Purple Giant Hyssop does best in mild temperatures. This isn't a plant that thrives in overly hot or dry conditions.


Unlike many cultivated garden species, the wild-in-origin Purple Giant Hyssop doesn't need fertilizer to flourish, especially if you ensure it's well-positioned in the right kind of soil, with the right kind of lighting.

Propagating Purple Giant Hyssop

Although this plant germinates well from seeds, cuttings can also do well. Make sure you select a cutting from the base of the stem. Ideally, this should be taken in late spring or through the fall. This is the only time when fertilization can be beneficial, as it can encourage a more rapid and successful establishment.


The Purple Giant Hyssop is thought to have been used to resolve digestive issues in Chinese medicine for many years.

The leaves are sometimes also added to soups, salads or teas as they have a distinctive fragrance and licorice-like flavoring. You can harvest the leaves any time through the summer months, but the best flavor is thought to be present around mid-summer when the plant has reached full bloom.

Being Grown in Containers

You can start the growth of Purple Giant Hyssop in containers. You'll just need to ensure whatever you select is deep enough to accommodate their large root system. The plant is forgiving enough to cope in a variety of potting soils—just look for something well-draining, and that isn't too rich.

Establishing the plant in containers cuts out the worry about it dying off because of competition from other surrounding species.

Growing From Seeds

Purple Giant Hyssop is known for germinating easily from seeds, although they do need to be broken from their dormancy. You can sow them indoors a couple of months before the end of the hard frosts and then easily transplant them into your garden.

Alternatively, you can sow them in the garden during Autumn. Autumn sowing ensures the seeds will have experienced a couple of months of cold stratification, and this will help encourage good growth. If you plan to plant the seeds out in spring, they do best if they have been kept refrigerated for a couple of months beforehand.

The seeds only need a very light soil and mulch covering, and they flourish in a moist and sunny position. Space the seeds out at least ten to twelve inches apart.