University of Maryland Extension

Bad Plant, Good Plant

Bad Plant, Good Plant

One of the most common definitions of a weed is "any plant growing where you don’t want it." This definition covers most situations, but did you know that sometimes the plants you love and deliberately plant can be harmful weeds? We are talking about "invasive exotic species," plants that originated from somewhere other than North America that are now growing in the U.S. to the point of crowding out our native plants in natural areas. Unfortunately there are a number of these plants, and you may even have inadvertently planted some of these in your landscape.

Not all non-native plants are bad to grow. In fact, many of the vegetables and fruits we grow are plants that the colonists brought with them to grow for food. What makes a non-native plant an "invasive exotic weed" is the propensity of these plants to out-compete everything in sight. They often green out earlier than native plants in the spring, shading out native plants. They also tend to produce copious quantities of seed that birds spread hither and yon. In addition to seeds, the plants may reproduce by sending out runners. And some of the plants even change the soil chemistry, making it impossible for other plants to grow there. Often there are no natural enemies to keep these plants in check. Once these plants get established, they can be very difficult to eliminate. Plants that are pulled may re-sprout from bits of root left behind, and seeds may persist in the soil for years before germinating.

You might wonder why we even care. Green plants are green plants, right? Well, as far as wildlife is concerned, not all plants are created equal. Our native critters evolved with our native plants, and that is what the animals can digest. For example, ninety percent of butterfly caterpillars can eat plants from only 3 families of plants. The best known example is the beautiful monarch butterfly. Its caterpillars can only eat milkweed. If there are no milkweed plants around on which the adult butterflies can lay its eggs, then there will be no new monarch butterflies. People that put in butterfly gardens tend to plant nectar plants to attract the adult butterflies, but it is equally important to provide the host plants that the caterpillars eat.

Caterpillars are important not only to the survival of butterfly species, but also to our native birds. Baby birds need a high-protein diet, and insects happen to be high in protein—twice the level of protein as beef! Without native plants for caterpillars and other insects to eat, we would lose our birds as well as our butterflies. Without insects, the whole food chain collapses. Even the diet of black bears is 23% insects.

So what are some of these invasive exotic weeds that threaten our native ecology? Here are some invasive exotic plants that people still buy and plant around their homes, unaware of the problems they create when the birds spread the seed to natural settings:

  • Japanese barberry (Berberis thunbergii)
  • Burning Bush (Euonymous alata)
  • Bradford pears (Pyrus calleryana)
  • Norway maples (Acer platanoides)
  • English Ivy (Hedera helix)
  • Porcelain Berry (Ampelopsis brevipedunculata)

You would be doing our environment a great service if you never buy or plant the above plants. Also, if you already have them growing, remove them and plant something native in their place. There are many native plants for about any type of growing site that are every bit as beautiful as the above invasive plants. Excellent resources for learning about native landscape plants for the Maryland piedmont area are available online at www.nps.gov/plants/pubs/chesapeake/pdf/chesapeakenatives.pdf‎ and at www.nps.gov/plants/pubs/nativesmd/pdf/MD-Piedmont.pdf‎.

Some examples of lovely native shrubs for the landscape are:

Blueberry bushes (Vaccinium corymbosum)
Flowers in the spring, blue berries in the summer (for you or the birds and critters) and red to maroon leaves in the fall. There are varieties that only get about 18 inches high and others that grow over six feet. What more could you want? See http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/n470/vaccinium-corymbosum-bluecrop.aspx for advice on planting multiple cultivars for more fruit.
Ninebark (Physocarpus opulifolius)
White or pink flowers, and some cultivars have colored leaves spring through fall. Wow! See http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/g840/physocarpus-opulifolius.aspx
Oakleaf hydrangea (hydrangea quercifolia)
Interesting leaves, peeling bark in winter, lovely flowers, and maroon fall color. That pretty much covers the year. Dwarf cultivars are available. See http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/d380/hydrangea-quercifolia.aspx.
Smooth hydrangea (Hydrangea arborescens ‘Annabelle’)
With huge snowball-like flowers.Pink-flowered cultivars are now available. See http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/s940/hydrangea-arborescens-annabelle.aspx.
Bushy St. John’s wort (Hypericum densiflorum)
Yellow blooms in summer. See http://www.mtcubacenter.org/plant-finder/details/hypericum-densiflorum.
Blackhaw viburnum (Viburnum prunifolium)
A small tree or large shrub, with lovely white flowers in the spring. See http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/plant-finder/plant-details/kc/g240/viburnum-prunifolium.aspx.

Now that you know that you can find great native plants for your landscape to replace those boring, in-everyone’s-yard invasive plants, you probably want to know where you can find them. The Maryland Native Plant Society lists nurseries that sell native plants--see http://mdflora.org/publications/nurseries.html. More and more, you can also find a selection of native plants at your local nurseries and garden stores. These native plants are usually easy to grow since they are naturally adapted to this area. The more kinds of native plants you grow, the more kinds of wildlife you support.& You many have a few insects that chew on the leaves, but as you now know, that is actually a good thing. It proves you are supporting our native ecosystem.

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