Landscapes and Invasive Plants
Rebecca Magron, Horticultural Consultant & Research Associate
Dated -
June 06 , 2007

We all know that weeds in the home garden are bad. Why, exactly, they are bad is not only due to the unaesthetic and discouraging sight of unwanted plants popping up in flower and vegetable gardens, but that they are also hazardous to desirable plants. Weeds may harbor pests and diseases that affect crops. They compete with garden plants for nutrients, light, and most critically, water. For example, a very large volume of water moves through an individual plant, so every single weed growing in a garden equals water lost that might otherwise have been available for the desired flowers, fruits or vegetables.

Physical removal, or “weeding”, and the use of mulches are tried and true methods of dealing with weeds. Cultivation by hand or hoe is effective especially when weeds are young, but this method means continuous vigilance and season long work. Mulching covers the soil surface to prevent weed germination and has an added advantage in helping conserve soil moisture.

What about the weeds in the landscape known as the invasive plants? Right now a major plant pest is really easy to spot. Roadways, hedgerows and other untended areas bloom white this month with multiflora rose ( Rosa multiflora). Perhaps the most predominant impact of multiflora rose is its success in crowding out native vegetation. An invasive plant typically has a vigorous growth habit that allows it to out-compete native vegetation and easily take over an area, sometimes entirely. Monostands of multiflora rose are undesirable since they choke out native vegetation and are of considerably less wildlife habitat value as a result.

Multiflora rose was introduced to the US from Japan in the late 1800’s for use as an ornamental and was later used for erosion control and living fences. Multiflora rose is a thorny perennial that reproduces by seed and tip layer. Seed dispersal by birds may account for its widespread invasion of fallow fields, pastures, hedge rows, no-till fields, and other uncultivated areas. It forms dense mounds 6 to 10 feet high and just as wide. It is not a true climber, but readily grows higher if nearby support (e.g., a tree) is available.

Homeowners with native landscaping are likely to find themselves battling multiflora rose. Control of this invasive species takes time, dedication and labor. Manual control of multiflora rose can be more easily accomplished with small stands than large. Small stands can be removed by hand and the roots dug out. Mowing and/or cutting several times during the growing season for a few years may be effective over the long term. However, be sure to replace with desired plants since their establishment may help in suppressing multiflora rose seed germination. Homeowners would also have to monitor the site for any multiflora rose emerging since removal is much easier when it is young. Appropriately labeled post emergent herbicides may also provide effective control of multiflora rose. However, in the home landscape, multiflora rose may be near or intermingled with desirable plants, and materials that kill multiflora rose can kill or damage these plants too. As always, the label is the law so carefully read and follow labels for proper use, recommended timing, rate and safety precautions.

For more information about weed control in the garden or landscape, call the Rutgers Master Gardener Helpline of Hunterdon County at 908-788-1735 Monday through Friday 9:00 am to 12:00 pm and Mondays and Wednesday from 12:30 pm to 3:30 pm or stop by the Rutgers Cooperative Extension office off Route 31 during those hours.