Controlling Invasive Plants

Controlling Invasive Herbs

Herbs become invasive in one of two ways. Some freely scatter their seeds, that seem to sprout with ease even in the most inhospitable conditions. Others send out rhizomes (root-like stems) that meander along just under the soil's surface; sprouting new plants as they go. Both are highly efficient ways to overrun your garden and choke out existing plants. Here are some ways to keep these invasive herbal companions in check.

Effective Methods of Control

• Plant them in pots. Individual herbs can be controlled easily by planting them in containers. The containers can then either be left above ground, or you can dig a hole in the garden and sink them into the ground, leaving an inch or two of the pot's rim above the soil line, so the stems won't creep over the edge and root in. A six inch pot with drainage holes is a good size to start with. Herbs in pots sunk into the ground should be dug up and repotted every 2 to 3 years to prevent the plants from becoming root bound.

• Smother them. Lay down a thick layer of mulch, newspaper, plastic, or landscaping fabric under mature herb plants to discourage seeds from sprouting and to smother young plants.
• Edge them out. Install plastic edging underground to stop herbs that spread via roots or runners. The edging must be planted fairly deep in the soil (at least 10 inches) or rhizomes will simply burrow underground and pop up a few feet away.
• Pinch them back. Stay one step ahead of invasive growth by pinching herbs back vigorously. This will prevent them from producing flowers and casting seed all over the garden.
• Deadhead them. Remove spent flowers as soon as they wilt to stop invasive plants from reseeding.

Dealing with Escape Artists

If you find that one of the invasive herbs in your garden has managed to escape, dig up the unwanted seedlings, making sure to remove the entire root system. Then sift through the soil with a digging fork to make sure you get any leftover pieces. Keep an eye on the area for several months, and either dig out any plants that reappear or clip them off at soil level and smother them for several weeks with a heavy layer of newspaper or a large, flat stone.

A Short List of Invasive Herbs

The following list of invasive herbs is not meant to be complete. In fact, in your region, the list may be much longer:

• Artemisia (Artemisia spp.)
• Bee Balm (Mondara spp.)
• Chives, garlic (Allium tuberosum)
• Comfrey (Symphytum officianle)
• Costmary (Chrysanthemum balsamita)
• Dandelion (Taraxacum officinale)
• Fennel (Foeniculum vulgare)
• German chamomile (Matricaria recutita)
• Herb-Robert (Geranium robertianum)
• Hops (Humulus lupulus)
• Horseradish (Armoracia rusticana)
• Kudzu (Pueraria montana var. lobata)
• Mints (Mentha spp.) (All members of the family, including pennyroyal, peppermint and spearmint)
• St. John's wort (Hypericum perforatum)
• Tansy (Tanacetum vulgare)
• Violet (Viola ordorata)
• Yarrow (Achillea spp.)

Catalogue Clues: When shopping for herbs in garden catalogs, invasive herbs should come with a warning (mint in particular), but they usually don't, so you'll need to do your homework as well as learn to read between the lines. Plant descriptions such as 'carefree", "vigorous", "establishes quickly", or 'grows anywhere" may be code for invasive tendencies. When acquiring herbs locally, consult other gardeners, local nurseries, and your local extension agent about herbs that are invasive in your area.

By Ellen Brown

Invasive Plants and How You Can Minimize Their Spread

Each year millions of dollars are spent, and tons of herbicides are applied, in what is sometimes a futile attempt to combat the spread of invasive plants. Here is what you need to know about the invasive plant problem and what you can do to help.

What Makes a Plant Invasive

Plants are classified as invasive when they have proved their ability to thrive and spread (aggressively) outside of their native range. Some plants spread slowly to only small areas and never really become a problem. Other plants are naturally aggressive in their native habitat. When these plants spread to outside their native range, they tend to be equally as aggressive. Before you know it, native plants (and the animals and insects that depend on them) are crowded out and biodiversity is lost. In areas where rare native species are already under pressure, the spread of invasive species can be the straw that breaks the camel's back.

Recognizing Invasive Plants

The 5 Characteristics of Invasive Plants:

1. They produce a large number of offspring each season.
2. They can tolerate a variety of soil types and climate conditions.
3. They spread easily.
4. The grow rapidly and easily overtake slower growing plants.
5. They spread aggressively when not constrained by the environmental checks and balances of their native habitat.

How Invasive Plants Spread

Invasive plants spread in a number of ways. Some were imported years ago and have never been fully eradicated. Others are introduced accidentally through agriculture and trade. And some are the result of well-intentioned horticultural practices gone bad (like selective breeding for traits of extreme resiliency).

What You Can Do

Learn to identify plants that are known to be invasive locally. Your local Department of Natural Resources should be able to supply you with information. There are also some great resources online, like http://www.invasive.org

Do your part. As soon as you notice an invasive species on your property remove it. If you see invasive plants in your neighborhood, volunteer to help other property owners remove them.

Choose plants for your landscape wisely. The behavior of a plant can vary widely from region to region. Always check a plantís invasive reputation before adding it to your landscape. What may be loved by one gardener (e.g. trumpet vine, monkey grass) may be a huge headache when planted in your zone.

Consider using native plants or non-invasive alternatives in your landscape.

By Ellen Brown

Prevent Invasive Plants From Taking Over

When planting a plant that is liable to take over your garden, it is best to get a small plastic bucket (such as ice cream comes in) and set it into a previously dug hole. Put small drainage holes in the container, then add part dirt mixed with fertilizer. Place the plant in the bucket and cover over the roots.

<P>Enjoy without having the invasive plant spread roots all over your garden. You can use any size container. I love many invasive plants and now can enjoy them.

By Edna McTeague from West Bath, ME

Gardening: Contain Your Mint

Many plants, especially herbs, are very invasive and will spread and quickly take over your garden. To prevent this, place the plant, like this spearmint, in a container. This mint is planted inside an old ice cream maker. I have a beautiful plant and don't have to worry about it taking over!

By Marilyn from Colfax, LA