Is Walker’s Low Catmint Invasive? A Close Look at This Popular Garden Plant

Walker’s Low Catmint (Nepeta x faassenii ‘Walker’s Low’) is an herbaceous perennial in the mint family that has become a staple in many home gardens. With its aromatic gray-green foliage and stunning indigo-blue flower spikes that bloom from late spring to fall, it’s easy to see why this plant is so beloved.

However, there has been some debate over whether Walker’s Low Catmint has the potential to become invasive in certain environments. As a responsible gardener, it’s important to understand the growth habits and reproductive mechanisms of any plant you choose to grow.

In this article, we’ll take a close look at Walker’s Low Catmint to determine just how invasive its tendencies are, and provide some tips on growing it without letting it get out of control

What Makes a Plant Invasive?

Before determining whether Walker’s Low Catmint is invasive, it’s helpful to understand what makes a plant invasive in the first place.

In general an invasive plant is one that is not native to a particular region, and once introduced is able to thrive and spread aggressively. Invasive plants reproduce rapidly, have high survival rates, and can adapt to a variety of environmental conditions. This allows them to establish quickly and outcompete native species.

Some common traits of invasive plants include:

• Fast growth and maturation rate
• Prolific reproduction through seeds, rhizomes, tubers, etc.
• Rapid spread over large areas
• Forming dense thickets that choke out other plants
• Lack of natural predators or controls to keep growth in check
  -Altering ecosystem functions, reducing biodiversity

Clearly, invasive plants can have major detrimental impacts on natural environments. Understanding the specific characteristics and growth habits of a plant will shed light on its invasive potential.

Is Walker’s Low Catmint Native?

Walker’s Low Catmint is not a native North American species. It was bred in England in the late 1930s as a hybrid between Nepeta faassenii (Faassen’s catmint) and Nepeta racemosa (racemed catmint), both of which originated from southern Europe.

Since Walker’s Low Catmint is not native to the United States or Canada, any propagation beyond intentional garden planting could be considered invasive spread. However, non-native plants are not inherently invasive. Many well-behaved ornamentals commonly grown in North American gardens originally came from other parts of the world.

So Walker’s Low Catmint’s non-native status alone does not confirm invasive tendencies – we need to look at its specific growth habits and reproductive mechanisms.

Growth Habits of Walker’s Low Catmint

One key factor when evaluating invasiveness is the plant’s growth rate and habits. Fast-growing, rapidly spreading plants are more likely to become invasive than slow growers.

Walker’s Low Catmint has a relatively moderate, compact growth habit. It reaches a mature size of 18-24 inches tall and 24-30 inches wide. The plant grows at a moderate rate, not nearly as quick as highly invasive plants like Japanese knotweed or purple loosestrife.

The compact, clumping form of Walker’s Low Catmint means it does not typically spread out aggressively through above-ground runners. It tends to stay where it is planted, expanding its clump slowly over time. Rapidly spreading rhizomes or stolons are characteristic of many invasive mint family members, but Walker’s Low Catmint does not exhibit this trait.

Overall, the modest growth rate and habit of Walker’s Low Catmint do not exhibit the aggressively spreading tendencies common in invasive plants.

Reproductive Mechanisms

Invasive plants are able to reproduce quickly and prolifically, generating high numbers of seeds, tubers, bulbs, or other propagules. They can also reproduce vegetatively through roots, rhizomes, and plant fragments.

Walker’s Low Catmint can spread through self-sown seeds. However, it does not produce the extremely large volumes of seeds characteristic of highly invasive plants. The seeds are not exceptionally long-lived, so they do not tend to build up heavily in the soil seed bank.

Walker’s Low Catmint lacks vigorous rhizomes and does not spread through vegetative fragments. The plant regenerates easily if divided during transplanting, but plant divisions and fragments do not readily break off and take root as they would in highly invasive mints.

Overall, while Walker’s Low Catmint can reproduce through self-sown seeds, its reproductive mechanisms are not aggressive enough to make it highly invasive. The plant does not spread prolifically through roots, rhizomes, or fragments.

Environmental Tolerance and Competitive Ability

Invasive plants are able to thrive in a wide range of environmental conditions, adapt to disturbance, and outcompete native species.

Walker’s Low Catmint does have some weedy qualities – it is tolerant of drought, heat, humidity, and poor soils. However, it does not exhibit the extremely vigorous competitive ability of notorious invasives.

The plant spreads slowly into open space, but does not aggressively choke out intact native plant communities. Healthy native ecosystems tend to limit its ability to take over an area. It may compete decently in disturbed habitats against other non-natives, but does not threaten most undisturbed native plant communities.

Lack of Natural Controls

In their native ranges, plants are often kept in check by diseases, insects, and herbivores that have co-evolved with them. But when plants are introduced to new regions, they may lack these natural controls, allowing them to spread rampantly.

Walker’s Low Catmint does not appear to have any major native insect pests or diseases helping control it in North America. However, it is susceptible to mint rust, a fungal disease that can disfigure its foliage during cool, wet conditions. Some generalist insect herbivores like leafhoppers, plant bugs, and caterpillars may feed on it, but not at levels that significantly limit growth.

So the lack of specialized natural controls does allow Walker’s Low Catmint to grow unrestrained. But due to its moderate growth habits, this alone is not enough for the plant to exhibit highly invasive tendencies. Natural controls would likely just keep the plant in check to its typical compact clumping form.

In Summary: Traits of Walker’s Low Catmint

• Not native to North America
• Moderate, compact growth habit
• Does not spread aggressively through runners or rhizomes
• Reproduces through self-sown seeds, but not prolifically
• Tolerates a range of conditions, but is not highly competitive
• Lacks specialized predators and diseases to control growth

Is Walker’s Low Catmint Considered Invasive?

Based on its specific traits and growth habits, most gardeners and botanists agree that Walker’s Low Catmint exhibits low invasive tendencies.

While it can spread through seeds into adjacent open areas, it does not grow or reproduce aggressively enough to invade intact native plant communities. Healthy native ecosystems are able to limit its spread. And in garden settings, it’s easy to control the modest self-sowing tendency through proper pruning, deadheading, and maintenance.

Walker’s Low Catmint has not been designated as invasive or noxious by any state or federal agencies. It has been grown extensively for many decades without exhibiting invasive behavior. However, it’s always wise to be vigilant and monitor the spread of any non-native plants, even well-behaved ones.

Tips for Growing Walker’s Low Catmint Non-Invasively

Here are some tips for growing Walker’s Low Catmint responsibly and preventing any unwanted spread:

• Plant in containers or areas bounded by driveways and walkways to prevent escape. Avoid planting directly against open native vegetation.

• Deadhead spent flowers before seeds set to reduce self-sowing.

• Monitor for and remove unwanted self-sown seedlings.

• Surround with slower growing perennials and grasses that can act as a living mulch to inhibit spread.

• In areas where mint family members are invasive, consider planting sterile cultivars that cannot self-sow or spread through roots and rhizomes.

The Verdict: A Well-Behaved Garden Plant

When grown properly and maintained responsibly, Walker’s Low Catmint makes an excellent non-invasive garden plant. It exhibits low potential for aggressive spread or invasion into natural areas.

This compact, fragrant perennial provides bountiful nectar for pollinators. And it adds wonderful texture and color to gardens with its handsome silver-green foliage and charming blue flower spikes.

While it’s always prudent to monitor the spread of non-native plants, Walker’s Low Catmint has shown itself to be a well-behaved landscape specimen. With its moderate growth habits and limited reproduction, this garden favorite can be enjoyed without fear of rampant invasion.