While perennials offer the convenience of planting once and enjoying years of beauty in your garden, some can become invasive and wreak havoc on your space. I’ve had my fair share of experiences with perennials that started out as lovely additions but eventually turned into pests. In fact, some of my favorite varieties grew beyond their welcome, spreading uncontrollably and becoming more trouble than they’re worth.
If you’re looking for ornamental perennials to approach with caution before planting, I’m happy to share my expertise and help you make informed decisions.
What Are Perennials?
Perennials are plants that have the unique ability to thrive for more than two years after being planted. Unlike annuals, which have a limited lifespan and typically bloom before dying off each year, perennials can spread out underground or creep into other areas of the garden over time. This means they can become invasive or overgrown if not properly controlled. Despite this potential drawback, perennials offer several advantages in the garden.
They require less maintenance compared to annuals, as they don’t need to be replanted every year. Additionally, perennials provide a sense of permanence and stability, as they remain a part of the garden’s landscape for an extended period. On the other hand, annuals offer a quick fix, providing instant coverage and filling empty spaces temporarily.
Perennials That Take Over Your Garden
When incorporating these plants into your garden, it’s essential to consider their potential for spreading and the challenges that come with removing them if needed. Before planting, take a moment to think about the location and surrounding environment. Will they have enough space to grow without encroaching on other areas? Are there any nearby obstacles or features you need to be mindful of? Having a clear understanding of these factors will help prevent future headaches.
And remember, utilizing containers can be an excellent way to control their growth and keep your garden tidy.
Nasturtium
Nasturtium (Tropaeolum spp.) is often viewed as an annual that self-seeds readily, but in warmer climates (USDA Growing Zones 9-11), this hardy perennial has a tendency to spread and take over entire gardens and landscapes. Its seeds drop constantly, giving rise to new plants amidst the older ones. As it grows, nasturtiums can quickly colonize surrounding areas. To keep them under control, it’s best to plant them in containers or restrict their spread by regular pruning.
While some may find this tendency overwhelming, others appreciate the lush foliage and vibrant blooms that nasturtiums bring to the garden. In my experience, I’ve learned to strike a balance between allowing these perennials to thrive while also keeping their spread manageable.
Bear’s Breeches
Bear’s breeches (Acanthus mollis) are notorious for forming dense clumps that can be nearly impossible to eradicate completely. Initially, they may require only three or four feet of space to grow, but they will soon spread beyond these boundaries and encroach on areas occupied by other plants, potentially outcompeting them for resources. Furthermore, their capacity to cast deep shade can also hinder the growth of smaller plants nearby.
Some regions have even classified bear’s breeches as an invasive species due to their ability to aggressively colonize new areas. While the plant does boast impressive, glossy green foliage and striking, upright flowers, one must carefully weigh these aesthetic charms against the potential drawbacks of its invasive tendencies.
Agapanthus
Agapanthus africanus is often utilized as a border plant or to fill gaps in landscaping, given its tendency to form dense clumps. This invasive nature is further exacerbated by the fact that it seeds readily and can be challenging to eradicate once established. As the rhizome roots spread beneath the soil, the plant rapidly populates an area, covering significant portions of the garden within a few seasons.
For those seeking to cultivate this variety in more controlled environments, several hybrid agapanthus species are suitable for container growth or indoor cultivation, allowing enthusiasts to bring this beauty into their lives.
Lamium
Lamium maculatum, a popular ground cover, has the ability to create a dense mat of foliage that can even outcompete some weeds for space. While this is beneficial in many ways, it’s not uncommon for the plant to spread beyond its intended boundaries over time – typically within five years or so. It’s essential to keep an eye on Lamium maculatum as it grows and maintain its boundaries to prevent encroachment into adjacent areas.
Mint
While many perennials are valued for their beauty and versatility, none are quite as infamous for their spreadability as mint (Mentha spp.). This hardy herb is notorious for its ability to quickly colonize new areas, often catching gardeners off guard. In fact, a small patch of mint planted in a vegetable garden can soon sprout up in unexpected places throughout the yard, including cracks in concrete, garden beds, and gaps in decking.
To keep this invasive tendency under control, it’s generally recommended to plant mint in containers – either buried in the ground or sitting on top – rather than directly into the soil. Even if you do choose to use a submerged pot, be sure it’s free of any cracks or crevices that might allow the mint to escape and spread even further.
Japanese Anemone
Despite its dainty appearance above ground, the Japanese anemone (Anemone hupehensis) has a more formidable reputation beneath. Its fibrous roots can spread rapidly and become challenging to eradicate once established. For this reason, it’s essential to carefully consider where you plant these flowers. If allowed to spread freely, they may quickly outcompete surrounding plants for resources.
A more controlled approach is recommended, such as planting them in containers or areas where their growth can be contained.
Wisteria
Wisteria, a woody climber native to China and known for evoking images of idyllic cottage gardens or luxurious English country estates, is a force to be reckoned with. Its aggressive growth habit allows it to spread and wrap itself around any available structure, including houses, which can lead to damage if not properly controlled. If allowed to twine itself around a tree, wisteria can ultimately prove fatal to the tree’s survival.
Additionally, its heavy vines can cause even sturdy trellises to topple if they become too weak or aged. While considered invasive in certain regions, wisteria is still widely available for purchase in many areas, making it a popular choice for gardeners and landscapers alike.
Tansy
Tansy (Tanacetum vulgare) is renowned for its natural pest-repellent properties, making it a popular choice as a companion plant. This perennial herbaceous plant is also believed to attract bees to the garden, supporting local pollinators. However, Tansy’s spreading habit means it can quickly take over other plants, paths, and lawns, requiring careful consideration when incorporating it into your garden design.
Obedient Plant
The Obedient Plant (Physostegia virginiana) is unique in its ability to be trained to face a specific direction, making it a popular choice among gardeners. One of the ways this clump-forming perennial propagates is through underground rhizomes, which allow it to spread rapidly and engulf nearby plants. Its aggressive growth habit means it can easily breach fences and encroach on neighboring areas.
If you’re interested in growing an Obedient Plant, consider opting for the ‘Miss Manners’ cultivar, which has been bred to remain compact and self-contained, eliminating the need for containment.
Lamb’s Ear
Lambs ear (Stachys byzantina) is often prized by gardeners due to its low-growing spreading habit. However, as it matures over several seasons, this very characteristic can become a liability. The plant’s propensity for spreading into lawns and other areas of the garden can lead to an unkempt appearance. Despite being one of the most charming perennials initially, lambs ear’s invasive nature means that there are likely more suitable options for gardeners seeking a low-maintenance design.
Bishop’s Weed/Snow On The Mountain
The bishop’s weed (Aegopodium podagraria) is an attractive ground cover due to its varied leaves, which can spread rapidly to cover a large area. However, this attractiveness comes with a caveat – it can be extremely difficult to eradicate once established. The plant’s ability to regrow quickly from underground rhizomes means that even small fragments left behind can lead to re-growth over time.
As such, it may take several seasons to completely remove the bishop’s weed from your garden, making its persistence a double-edged sword.
Ostrich Fern
While ostrich ferns (Matteuccia struthiopteris) are often touted as hardy perennials, they also possess a more sinister trait: invasiveness. Despite their striking appearance, these plants have a tendency to dominate and overpower other vegetation in your garden. A clever gardener will strategically plant them in areas where native flora may struggle to thrive, such as cool or damp wooded zones.
Be aware that ostrich ferns can quickly spread through underground rhizomes, effectively taking over the surrounding area.
Creeping Bellflower
Creeping bellflower (Campanula elegans) is notorious for its ability to spread rapidly and outcompete native species. Despite being considered an invasive weed in many regions, it’s often found in gardens due to its attractive flowers and perennial nature.
This hardy plant has a remarkable ability to regenerate from small fragments of root left behind after attempted removal. Its long taproot can break off if pulled, only to continue growing underground before re-emerging and spreading anew.
This persistence makes it notoriously difficult to eradicate completely.
If someone offers you a free creeping bellflower, be cautious and politely decline the gift. Be aware that accepting this ‘free’ plant may ultimately lead to an unwanted invasion in your own garden or nearby environment.
Borage
While some gardeners may find borage (Borago officinalis) a delight to cultivate, its propensity for spreading can be overwhelming. As an annual in cooler climates or a short-lived perennial in warmer regions, this herb has a tendency to sprout up unexpectedly. Its seeds are easily dispersed, resulting in the plant popping up in multiple locations.
While young seedlings can be pulled out with relative ease, older plants tend to break off when attempted to be removed, making them less than ideal for gardeners seeking low-maintenance results.
Comfrey
Comfrey (Symphytum officinale) may initially appear to be a laid-back plant, as it grows at a moderate pace before dying back over winter. However, this is just a ruse – the following year, it will return with a vengeance, doubling in size and spreading its roots far and wide. The plant’s rapid underground expansion can catch even the most vigilant gardener off guard, especially if they don’t take steps to control its growth.
In fact, if you’re not careful, comfrey can quickly take over an entire area, as I discovered when I accidentally let it spread down a bank. If you do want to cultivate comfrey, but don’t want it to get out of hand, the solution is simple: plant it in a container and keep its ambitions in check.
5 Tips for Planting Perennials
When selecting perennials, be mindful of their mature size, spreading habits, and potential for replication. Factors like your growing zone and environment can significantly impact a plant’s invasiveness. What may be considered invasive in one area might not pose the same issue in another. To accommodate spreaders, choose an area of your garden where the rhizomes can thrive without becoming unwieldy. Keep in mind that removing these perennials can take time – think two to three seasons.
For those with limited space or a desire to keep things contained, consider planting in pots and taking precautions to prevent root growth beyond the container’s base.
