Agastache Spreading Habits Explained

Commonly Hummingbird Mint, this beloved perennial prized for its fragrant foliage, nectar-rich blooms, and appeal to pollinators like bees, butterflies, and—of course—hummingbirds. But as Agastache gains popularity among gardeners, a common question arises: Is it invasive?

The answer is nuanced and depends on the species, your growing conditions, and how the plant is managed. Agastache isn’t invasive in the scary, take-over-your-yard sense like kudzu or Japanese knotweed, but some types are enthusiastic self-seeders if conditions are right. In this Garden Blog, we will cover how Agastache grows, spreads, and how to manage it is key to keeping this vibrant bloomer under control in your garden.

By: Reggie Meehan (11/10/2025) - Last Updated (1/4/2026)

How Agastache Spreads

Agastache behaves very differently depending on where you give it a home. In the right conditions, it can be enthusiastic—but once you understand how it spreads, it’s easy to stay a step ahead of it.

Seed Dispersal

Most Agastache varieties spread primarily by seed, which is where gardeners are most likely to be surprised. After flowering, spent blooms dry on the stalk and drop seed naturally, especially if flower spikes are left standing in the Fall. In open, sunny soil with good airflow, those seeds can germinate the following Spring.

That said, seed dispersal isn’t automatic chaos. Seedlings tend to appear in lightly mulched or undisturbed areas rather than densely planted beds. Regular deadheading, thicker mulch, or compacted soil dramatically reduces reseeding. I will allow a few seedlings to remain, provided they land somewhere useful—it’s an easy way to let the garden evolve naturally without losing control.

Root Expansion

Below ground, Agastache is not an aggressive spreaders; it grows as a clump, slowly expanding outward from the original crown as the plant matures and gains strength over several seasons. Over time, those clumps can widen and become dense, especially in ideal sun and drainage. I’ve seen mature plants start to crowd smaller perennials if they’re packed too closely, but that’s more a spacing issue than a takeover.

Every few years, I’ll lift and divide larger clumps—not because I have to, but because it keeps the plant vigorous and gives me extras to replant or share. When managed this way, Agastache stays well-behaved and predictable, even at full size.

Conditions that Encourage Agastache to Spread

Dry vs. Humid Climates

In most of North America, Agastache is not considered invasive or a threat to native ecosystems. However, I would encourage a little extra awareness in dry western regions like Colorado, Utah, and parts of California. In those climates, Agastache thrives in the same lean, open conditions found in natural landscapes, which makes it easier for seed to move beyond the garden bed.

In contrast, here in the Southeast and other humid zones, it’s usually far less of an issue. Heavier soils, denser plantings, and shorter plant lifespans naturally keep Agastache in check, so it behaves more like a polite garden perennial than a wanderer.

Signs That Agastache May Be Spreading Too Much

If you’re growing Agastache and wondering whether it’s becoming too aggressive, watch for:

• New seedlings sprouting in unexpected places each spring
  

• Dense clump expansion crowding out other plants
  

• Persistent reseeding despite your efforts to thin or remove spent plants
  

• Flower heads that dry on the stalk and drop seed into surrounding mulch

How to Control Agastache’s Spread

While Agastache doesn’t demand the same constant attention as true invasive plants, it still benefits from mindful management. When left completely unattended, its ability to self-seed and expand by clumping can cause it to edge into neighboring spaces. With a few easy habits, you can keep your Hummingbird Mint thriving exactly where you want it—without sacrificing its beauty or vigor.

Deadhead Flowers Promptly

The most effective way to control Agastache’s spread is timely deadheading. Once flower spikes fade, trim them before seeds mature to stop self-seeding and prevent unwanted seedlings next spring. Regular deadheading also encourages new blooms, keeping plants vibrant from midsummer through fall. Many gardeners enjoy cutting fresh stems for arrangements, while dried seed heads add fragrance and texture to wreaths or potpourri.

Thin and Divide Clumps

Every 2–3 years, it’s best to dig up and divide the plant in early spring before new growth starts or in fall after flowering ends. Dividing reduces overcrowding, encourages healthier root systems, and limits the plant’s footprint. To divide, lift the root ball with a spade or garden fork, separate it into smaller sections with several healthy shoots per division, and replant them in fresh, amended soil. This technique not only helps control spread but also provides free new plants for other areas of your garden or to share with friends.

Use Mulch to Prevent Germination

A 2–3 inch layer of mulch creates a strong barrier against unwanted seedlings by blocking sunlight and limiting soil contact. Organic options like bark, pine straw, or composted leaves also help retain moisture, suppress weeds, and regulate temperature. Refresh mulch each spring, leaving a small gap around the crown to prevent rot, for a tidy bed where Agastache stays lush, contained, and right where you want it.

Choose Controlled Agastache Varieties

Not all Agastache behave the same. Hybrid cultivars bred for ornamental use often have sterile or low-fertility seed production, meaning they won’t spread nearly as much as their wilder cousins. Here are a few top choices that offer beauty without aggressive self-seeding:

Black Adder

A refined hybrid with deep violet-blue spikes and a clumping form that stays put,  'Black Adder’ rarely reseeds even in ideal conditions. I like using it as a vertical anchor in mixed borders because it holds its shape season after season without wandering.

Blue Boa

Award-winning and sterile, this variety produces dense blue-purple blooms all summer with virtually no self-seeding. 'Blue Boa’ is also excellent for attracting hummingbirds while remaining one of the most predictable Agastache in the garden.

Blue Fortune

Agastache ‘Blue Fortune’ is a classic hybrid between Agastache foeniculum and Agastche rugosa, famous for its long bloom time, non-invasive habit, and heavy pollinator traffic. It’s one of my most reliable choices for gardeners who want color and movement without worrying about spread.

Kudos™ Series

Bred specifically for garden performance and sterility; these hybrids such as ‘Kudos Coral’ and ‘Kudos Mandarin’ stay tidy, bloom profusely, and resist reseeding. These are ideal for more structured beds where consistency and control matter.

Little Adder

Agastache ‘Little Adder’ is a compact and controlled version of ‘Black Adder,’ ideal for smaller spaces or borders where spread would be a concern. It delivers the same rich color and pollinator appeal in a more restrained, easy-to-manage form.

Enjoy Agastache Responsibly

Agastache is a stunning, fragrant addition to pollinator gardens, cottage borders, and xeriscapes. While it’s not considered a high-risk invasive, some species and varieties can spread more than intended through self-seeding or clump expansion. With a few thoughtful strategies—like pruning, selecting non-invasive hybrids, and monitoring spread—you can enjoy the full charm of Anise Hyssop and Hummingbird Mint without worry. Gardeners who respect this plant’s strengths will be rewarded with seasons of vibrant color, hummingbird activity, and delightful fragrance—all while keeping their garden in balance.