Horticulture

Background

Horticulture is a significant pathway for the introduction and spread of invasive species on PEI and across North America. Several of the invasive species causing damage in our natural areas on PEI first arrived here for use in gardens, with many still widely sold and planted today. Horticultural plants including flowers, grasses, trees, shrubs, ferns, and nonvascular plants are valued and selected for their aesthetic beauty and growing conditions. However, some species, when they escape containment, can become invasive in an ecosystem.

To protect PEI’s natural resources, wildlife, beauty, and ecosystem services, it is crucial that invasive species are not purchased, imported, planted, or introduced.

How They Spread

In a garden setting, invasive plants may seem contained to their beds or pots. You may not see them growing out of place around your property, but plants have evolved to reproduce and spread. Plants can move to new areas beyond our control in a variety of ways. Invasive plants can be spread over long distances by wind, water, pets, and wildlife. Invasive plants may also move into new areas through contaminated soil, compost that contains plant parts, or when garden waste is dumped in a natural area.

Impacts

Environmental Impacts
Invasive horticultural plants can fundamentally alter PEI’s ecosystems by displacing native plant species, reducing biodiversity, and harming wildlife that depend on native plants for food and shelter. They can also alter soil chemistry, water flow, and nutrient cycling which further destabilise the ecosystem.

Forestry Impacts
Invasive horticultural plants can affect the forestry industry by directly competing with forest crops, introducing pests, and interfering with forest regeneration. Invasive groundcovers, such as periwinkle, can dominate the forest understory and limit the germination of tree seedlings and other plants.

Agricultural Impacts
Invasive plants can cause issues in an agricultural context by reducing yields and increasing management costs for farmers. Some invasive horticultural plants can harbor diseases that affect particular crops. For example, common barberry was an ornamental plant that has been prohibited from sale due to its role as the host plant for black stem rust, a devastating disease in cereal crop production.

Horticulture Industry Impacts
The importation of plant stock can be a risk to the horticulture industry itself. Bringing in plants from off-island presents the risk of introducing invasive pests and diseases which may be housed in the soil or on the plant itself. A good example of this is the recent introduction on the box tree month which arrived on imported boxwood shrubs from Ontario.

Seed Mixes

Wildflower seed mixes often contain invasive species. Gardeners are usually unaware of this because even if they read the information provided on the outside of the seed packet, the package usually contains very little information about which plant species are actually inside. When information is provided, it is often inaccurate and generally not very specific. For instance, common names may be provided on a packet, but these are not reliable references. As an example, the name “daisy” may refer to any number of “daisy-like” flowers. One such daisy is ox-eye daisy, Leucanthemum vulgare, which is a highly invasive weed.

Another problem with wildflower seed mixes is that the term “wildflower” is often misinterpreted. “Wildflower” may imply to some gardeners that the plants in the packet are native to their area when in reality they may not be. It also may imply that they should be planted in the “wild”. In addition, some packets are specifically marked as “native” or “regional”. This can create problems as plants that are native to the area where the packets were manufactured may not be native to the area where the packets are being sold. This can be difficult to rectify, as the manufacturing location is sometimes not included on the packet.

Instead of purchasing wildflower seed mixes for your garden, try buying single-species seed packets that are labeled properly with common names AND scientific names. That way you can ensure you know exactly what you are getting and can determine whether the plants are native and non-invasive.

Native Plants

Choosing to plant native species in your garden is always the best choice. Native plants are an essential part of PEI’s ecosystem, providing food and habitat for birds, bees, butterflies, and other wildlife. Incorporating native species into your garden contributes to local biodiversity, ensuring these creatures have the resources they need to thrive. Native plants are also a part of our Island’s unique character and heritage, reflecting the beauty of PEI’s landscapes and offering an authentic aesthetic that blends with our natural environment.

By choosing native plants for your garden, you can create a stunning outdoor space and contribute to the health of the local ecosystem! To purchase native plants, look out for plants with the PEIISC native plant tag.

To learn more about the native or non-native status of plants you might find on PEI, refer to the Atlantic Canada Conservation Data Centre’s conservation ranks list for Prince Edward Island.

Exotic vs Invasive Plants

At a typical nursery or garden centre on PEI, most of your buying options will be exotic plants. These are plants that do not naturally or historically occur on PEI. Just because a plant is exotic, does not mean it is invasive. In fact, most exotic plants are not currently recognized as invasive and are generally safe to plant. But even if a plant does not appear to be invasive, it is important to note that our climate is changing. Species that may not be invasive in a particular area now could become invasive there in the future. These are referred to as “sleeper species”, and are another example of why it is always best to choose a native plant species for your garden.

Key Species

Below are some of the most common invasive species you may come across while plant shopping and might not realise are invasive.

Plant Shopping on PEI

At most garden centres across PEI, you will see a mix of native, exotic, and invasive plants for sale. Typically these options are not labelled as such, and it is the customer’s responsibility to do their own research on their selections before making a purchase. Before you purchase a plant, be sure to:

Research the species using its scientific name (if available) to find out if it’s invasive. Many exotic plants go by various common names which may not return accurate search results.
Check the plant and its soil for insects, invertebrates, or pathogens of concern. Sometimes the plant itself may not be an invasive species, but things hitchhiking along with the plant may be!
Ask the staff about the plant and where it was sourced from. Plants coming from off-island can present a higher risk of bringing new ‘hitchhiking’ insects or pathogens along with them.
Look for plants with the PEIISC native plant tag to be sure you are buying a plant native to Prince Edward Island.

Responsible Gardening

Plant only native or non-invasive species.
Do not dump any garden waste in natural areas.
Dispose of invasive plants with your garbage (black waste bin, or directly to a disposal depot) only. Never dispose of invasive plants in the compost (green bin). Bag plant material in clear plastic bags and label the bags ‘Invasive species’ with a permanent marker. Set the bags out with your regular residential black waste bin pick-up. Larger amounts can be brought to an Island Waste Management Corp. disposal facility, or the PEI Energy Systems incinerator on Riverside Drive Charlottetown with a special waste permit https://www.princeedwardisland.ca/en/information/environment-energy-and-climate-action/special-waste-disposal-permit. For these loads, there is an associated disposal fee based on weight provided at the disposal depot.
Manage, control, and remove invasive plant species from your gardens.
If you must keep invasive species: keep them contained to your garden bed, remove and dispose of any seeds or berries annually. Cut the flowers off as they die back but before they produce seed. If berries are the attractive part of the plant, remove them before they disperse their seed or are picked off by local wildlife. Dispose of all plant material in the garbage as described above.

Regulations

Some may be surprised to learn that there are few regulations preventing the sale of invasive species that harm our ecosystems. In PEI, only purple loosestrife and members of its genus, Lythrum, are regulated under the Weed Control Act. This act makes it an offence for any person to import, propagate, or sell these plants. For more information, refer to the full Weed Control Act – Purple Loosestrife Control Regulations.

The Canadian Food Inspection Agency (CFIA) establishes and maintains federal policies and standards for the horticulture industry to prevent the introduction and spread of regulated pests into Canada. Learn more here: CFIA Horticulture page

Information for Industry

Plant Wise is a national program that supports the (ornamental) horticulture industry’s transition to becoming invasive-free. The program helps both gardeners and industry understand which plants are invasive and harmful to our ecosystems, and to make ‘Plant Wise’ choices. To learn more visit the Canadian Council on Invasive Species Plant Wise page

If you are a PEI business that would like to be involved in reducing the spread of invasive plants, please contact the PEIISC directly at peiinvasives@gmail.com to learn more. We would love to work with you!