Clean beds along with proper use of mulch and pre-emergent herbicides is the best defense against landscape bed weeds.

It’s an unfortunate fact every lawn care operator knows to be true:

“There is no way to control weeds 100 percent,” says Miles Rush, partner and branch manager for WeedPro in Lewis Center, Ohio. “You will always deal with weeds.”

But there are steps LCOs can take to keep landscape bed weeds at bay. The first is to start with a clean slate by removing any weeds that may be present, said Dan Loughner, turf and ornamental business development leader for Dow AgroSciences. The next step is a fresh layer of mulch topped with an application of a pre-emergent herbicide.

“Pre-emergent herbicides are the first line of defense once beds are cleaned up, and should be applied on top of mulch,” says Loughner. “The mulch prevents annual weeds from germinating and coming through the mulch, but if weeds blow into the mulch, the herbicide will prevent them from becoming established. In the case of some perennial weeds, there are post-emergent products that can be used specifically for grasses that won’t hurt broadleaf plants in the beds.”

Rush agrees that a layer of mulch helps the soil retain moisture and prevents weed germination by keeping the ground cooler and acting as a barrier from the sun. Mulch also adds organic materials to a bed as it breaks down. Once the mulch has settled, Rush advises LCOs not to disturb or turn it because this process allows air and sunlight to reach the soil and can stimulate weed growth.

“If you have a nice layer of mulch that solidifies, people like to turn it,” Rush says. “But if you disturb the mulch, you are asking for weeds.”

Should a weed sprout, Rush advises spraying it with a postemergent herbicide rather than pulling it. When pulling live weeds, it’s difficult to remove the entire plant – often times a tap root will be left behind, which means more weeds to come. There are selective and non-selective herbicides and LCOs should educate themselves about the products they are using to avoid damaging other plants in the bed.

“There are winter, late-spring/early-summer, and late-summer/early-fall weeds that require certain chemicals and timing of application,” says Barbara Fair, extension horticulture specialist and assistant professor at NC State University in Raleigh, N.C. “In landscape beds, applicators must be careful to select proper chemicals because there are many other plants that can be negatively affected or even die if the incorrect herbicide is used and if it is applied incorrectly.”

Timing is Everything

Lawn care experts agree that pre-emergent herbicides should be applied early in the season, before weeds even have an opportunity to sprout. Post-emergent herbicides can be used “whenever you see green,” Rush says, adding that the sooner a weed is treated, the easier it will be to control. For maximum effectiveness, Rush advises not using herbicides on wet or rainy days.

“It’s not necessarily a problem, but you want to avoid any chance of the product missing the intended target or not killing the weed at all because it washed away,” he says. “This will cost you time and money, and your customers will still see weeds.”

When it comes to fertilizing a plant, Fair says LCOs should ask themselves, “Why I am doing this and what will the plant’s response be?” Annuals are grown for flowers, so LCOs should apply a fertilizer with sufficient phosphorous to stimulate flower production. Woody plants do not typically need to be fertilized as frequently as herbaceous plants, and older trees may need very low rates of fertilizer applied once a year, or split in half twice a year, she added.

“Fertilizing turf is different than fertilizing woody plants, perennials or annuals,” Fair says. “In general, applicators should apply fertilizers based on the results of a soil test, and during the growing season when the plant can make the best use of the nutrients.”

Rush agrees that the best time to apply fertilizer is in the spring and fall when plants are actively growing and temperatures are mild. Spring fertilizer applications help promote leaf, flower and tissue growth, while fall applications encourage root growth and help the plant store energy for spring. Trying to push growth during hot, dry summer months, Rush says, makes plants more susceptible to stress, disease and insect infestations.

“You want to apply fertilizer in the spring and fall because that is when plants are most actively growing and temperatures are not extreme enough to impact new growth,” he says. “I would not suggest any significant feed in the summer.”

Summer is also prime time for insects to feed on the leaf tissue of plants within the landscape, so LCOs should be aware of different methods of insect control. Loughner says some LCOs consider insect control to be an add-on service, and any problems should be discussed with the homeowner and treated on an as-needed basis.

“Often insect control is more of an aesthetic situation, and should be done as needed depending on how severe the damage is,” he says. “Insects don’t always come back to the same spot and, in a lot of cases, they don’t cause enough aesthetic damage to require treatment – except for Japanese beetles, especially on roses.”

Fair says LCOs should work with their clients to determine what threshold of insects is acceptable in the landscape, as it may not be high enough to warrant chemical control. Insect infestations also depend on the aggressive nature of the insect species, and whether it attacks healthy or stressed plants. The implementation of an integrated pest management (IPM) plan will help LCOs find insects when populations are low and easily treatable.

“Most insects are quite controllable either through mechanical, cultural, or chemical means,” Fair says. “Control insects when populations are low. Be sure you know the insect and the plant.”