Alien invaders

LITTLE ROCK — Low maintenance, great beauty - these are attributes gardeners look for when choosing plants. But a pretty plant can grow too well.

Some attractive species will take over everything in the garden, where they join the ranks of invasive plants.

On average, 85 percent of the invasive plants that are smothering Arkansas’ natural areas are not native. Most were intentionally planted and then escaped.

Left unchecked, these fast-spreading invasives begin to choke out native vegetation, which can in turn hurt native bees, butterflies and animals.

If you drove around the state this spring, you saw a plethora of white. Two plants that were absolutely everywhere were (and still are) the common privet (Ligustrum sinense) and the flowering pear (Pyrus calleryana).

PRODUCTIVE PRIVET

Privet was planted as a low-maintenance hedge in the ’30s and ’40s. With its small, mostly evergreen foliage and beautiful clusters of white, spirea-like blossoms in the spring, it was highly prized and graced landscapes across the South. Drought-tolerant, sun- or shade-tolerant, it grew like a weed - and thus became a weed.

All of those beautiful white flowers we saw this spring have set a profusion of small black fruits, which the birds consume. Then birds drop the seeds in every park, roadside and neighborhood.

The cycle then repeats itself, and privet is quickly consuming native vegetation as it spreads.

Ornamental pears have been prized for their perfect teardrop shape, white flowers in the spring and outstanding fall color.

While most gardeners call all flowering pear trees “Bradford pears,” that is simply one selection. There are many others. The parentage of all these trees begins with the Callery pear (Pyrus calleryana).

The flowering pears that now blanket our roadsides come from the seeds of all the Bradford and other ornamental pears that were planted as ornamental trees.

Fruit size can vary from BB-size to the size of a half dollar coin. Birds eat the fruit, drop the seed, and seedling pears emerge.

The trees have thorns, usually begin blooming between 3 and 5 years of age, and history repeats the spread.

In addition, we now know that the pear trees we intentionally plant fall apart easily in high winds and winter storms, and so these are not great trees to plant in Arkansas in the first place.

CLIMATE CONTROL

Invasive species vary from region to region.

Limiting factors or natural controls preventing rampant growth include:

Winter hardiness.

Summer heat and drought tolerance.

Moisture requirements.

Required soil pH and soil type.

Attractiveness to insects or animals.

When a new plant is introduced into a totally new environment, sometimes the natural checks and balances on it are not present, and the plant is given free rein to grow - in some cases, into a reign of terror.

THINK KUDZU

To celebrate the 100th birthday of the United States, other nations were invited to the Centennial Exposition in Philadelphia. The Japanese government constructed a beautiful garden filled with native plants, including kudzu.

Kudzu has large showy leaves and fragrant blossoms. American gardeners (just like today) wanted something unique and new and so they began planting kudzu as an ornamental vine.

In the 1930s, the federal Soil Conservation Service promoted kudzu for erosion control and hired the Civilian Conservation Corps to plant kudzu across the South. It was thought of as the miracle vine. Farmers planted acres of the stuff to feed livestock.

It wasn’t until 1953 that the government put out warnings against the plant, and it wasn’t until 1972 that kudzu was officially declared a weed.

The problem with kudzu is it grows too well in the Southeast - up to a foot a day during the warm months. Today, kudzu has crawled over some 7 million acres and is nearly impossible to control.

MODERN MONSTERS

While most gardeners today would not plant privet, kudzu or Japanese honeysuckle, they are still planting Bradford pears at an alarming rate, and royal Paulownia or empress tree (Paulownia tomentosa).

They allow mimosa and Chinese tallow trees to grow for the showy flowers or fruit.

People still plant bamboo, thinking they want a fast-growing screen and they can control it; but then it controls their and their neighbor’s yard.

Bamboo comes in a variety of forms, and while clumping bamboo can be controlled, running bamboo will sprout new growth anywhere out to a diameter equal to the height of the first plant.

So think, an 80-foot-tall bamboo can sprout 80 feet in all directions.

With all of these, planter and neighbor beware!

HIGH MAINTENANCE

Other invasive plants that are still common in landscapes include Vinca major, a fast-spreading ground cover for the shade. Give it a little water, and it can take over.

English ivy can spread up the trees, onto your house and all over the garden; and wisteria, if allowed to grow unchecked, will overtake everything in its path.

Mint is notorious for spreading beyond where it was planted, and if you give horsetail (Equisetum) even a little care, it becomes a marauding invader.

BUYER BEWARE

Our love of the new and exotic has us planting a whole host of plants we really don’t know much about. Who knows when the next kudzu will land in our yards?

Think about some recent introductions that have gotten a bit too happy:

Limelight artemisia has beautiful yellow and green foliage, but will quickly take over a garden, as will the running form of monkey grass, Liriope spicata.

Obedient plant (Physostegia) is anything but obedient, quickly spreading by underground roots and seeds.

The type of care a plant gets also can determine how fast it spreads. In dry conditions, chameleon plant (Houttuynia cordata) is fairly well behaved, but plant it in a moist area, and it will escape quickly.

SUSPECT TRAITS

Keep in mind that not all non-natives are invasive, nor are all natives well behaved.

Invasive plants typically tolerate a wide range of weather and soil types, multiply rapidly and produce a large amount of seeds, which are spread easily and efficiently by wind, water or animals.

The seeds usually germinate with ease and establish themselves quickly.

Invasive plants typically are fast growing, which allows them to displace slower growing plants.

Scientists have yet to predict which new plants will become invasive and where, often sounding an alarm too late. So when planting new introductions, it is important that you monitor their growth.

If a plant begins to spread or take over, it is easy (or easier) to control when it’s young. Once the thing’s established, its spread will be greater and stronger each year. Early detection allows for eradication, but if left to grow unchecked, an invader can become difficult to control.

RESPONSIBLE GARDENING

The key in landscaping is planting the right plant in the right place, while knowing the care needed. If you simply must use a quick spreader, contain it - put it in a container or plant in an area with borders to limit its spread.

Be a good neighbor and don’t plant something that will consume your neighborhood and the parks beyond.

Easy care and beauty are possible to achieve without using invasives. We have so many less treacherous nonnative plants to choose from; the possibilities are endless. And we have a whole host of wonderful native plants that we would like to see survive for our grandchildren to enjoy. It makes sense to monitor our gardens.