By Mark Czarnota
University of Georgia
The weeds in pansy plantings are usually annual plants such as common chickweed and annual bluegrass. In small plantings, most can easily be controlled with mulches and occasional hand weeding.
In larger plantings, though, people often turn to herbicides to control their weed problems. The number of chemicals you can use in pansies is limited.
A few pre-emergent products are out there: Dimension (dithiopyr), Pendulum and Corral (pendimethalin), Pennant (metolachlor), Snapshot (isoxaben and trifluralin), Surflan (oryzalin) and XL (benefin and oryzalin).
That's allThe list is short. But these products can provide excellent control of many weeds coming from seed. They're designed to control germinating seeds. They need a rain or watering of about an inch within a week of when you apply them.
Some of them come in both granular and sprayable forms. Granular herbicides are more popular with homeowners. They don't require any mixing. And they're more forgiving when you don't apply them just right.
None of these products, though, control all possible weeds. There are no "silver bullets" when it comes to herbicides. Most of these products or combinations of them will control 80 percent to 95 percent of the weeds from seed.
You will likely have some weeds you can't control with pre-emergent herbicides. But most of those can be easily removed by hand.
'Established'All of these products are meant to be used on established pansies. The plants have to be in the ground for some time, and the soil has to be settled around the root ball. You can settle the soil by firmly pressing it around the root ball as you plant and then watering the plants in.
Labels often stress that word "established." The key is to avoid letting pre-emergent herbicides reach the roots of plants.
Once weed grasses have emerged in pansy beds, only one product is labeled to control them: Vantage (sethoxydim).
Vantage is mixed with water and sprayed over the top of pansies to control emerged and actively growing grasses. It won't keep seeds from germinating.
Don't apply Vantage on hot, sunny days. It can cause minor damage to pansy plants then.
But wait...All of these herbicides were labeled for use on pansies when this article was written. But labeling can change. Make sure you read and understand the label before using any pesticide.
As herbicides go off patent, many third-party manufacturers may market them under different trade names. Glyphosate, the active ingredient in Roundup, for instance, is now available in more than 50 formulations.
Before using any herbicide, always consider the health of the plant. Make sure to consider the plants' cultural requirements, too. A quick canopy of pansy flowers and foliage will help outcompete the weeds.
Plant pansies where they'll get only 4 to 6 hours of direct sunlight. Make sure the site drains well and the soil is amended with some organic matter. Test the soil. Make sure the pansies are getting adequate fertilization.
Most important, make sure the pansy bed is mulched after you plant. Besides adding organic matter and maintaining soil moisture and temperature, mulches help keep weeds from germinating.
A good 2-inch layer of pine bark, pine straw, or shredded hardwood bark should help make for healthy, happy pansies.
(Mark Czarnota is an ornamental weed control specialist with the University of Georgia College of Agricultural and Environmental Sciences.)
(Mark Czarnota is an extension horticulturist with the University of Georgia College of Agricultural and Environmental Sciences.)