Weed control on ornamental beds can be difficult, because there are commonly a variety of plant
species, including annuals and perennials all in one bed.
Like with most things, a little bit of knowledge and preparation can go a long way in helping
you tackle these situations.
Most landscape maintenance contractors depend on a combination of landscape fabric, mulches,
and good old fashioned hand pulling to control weeds in the planter beds.
In addition, they help minimize weed growth by following a pre and post-emergent herbicide
program.
Your weed management program depends on the species of plants used in the bed and the
weeds you want to control.
Pre-emergent herbicides used for weed control and turf are not always suited for use in
beds, so it's important to always read the label to verify that the product is safe for
your application.
You can also contact your local county cooperative extension office to determine the tolerance
of an ornamental plant species to a given herbicide.
Some of these herbicides can be combined to increase the spectrum of weeds controlled
and provide effective control of annual grasses and many broad leaf weeds.
A few of these combinations can currently be found in premixed formulations from the
manufacturer.
Available in both liquid and granular forms, pre-emergents work by forming a barrier above
the seeds that can last for several months.
As the seedlings come into contact with the barriers, they absorb some of the herbicide,
which inhibits root growth.
As an added benefit, weeds that are pre-emergently controlled do not have the opportunity to
produce new seed.
Keep in mind, when choosing your product form, that granular herbicides have less drift and
are often more acceptable to the public than spraying.
They also pose less risk of crop damage than post-emergents.
Knowing the life cycle of the weeds you're contending with will help you determine the
most effective time to treat the bed.
For summer annuals, like crabgrass that begin germinating in the spring, applications of
pre-emergents are most successful when done in late winter or early spring.
A good rule of thumb is to treat the area when the temperature of the top 2 inches of
soil averages 55 degrees over several days.
In addition to managing crabgrass, these treatments will also help prevent perennial seedlings
from germinating.
To manage weeds that grow in the winter months such as annual bluegrass, late summer or early
fall applications will work best.
Unfortunately, weed seeds don't all germinate on the same day, so you may need to make multiple
applications or use an herbicide that can persist throughout your growing season.
It is important to note that most pre-emergents need to be watered in so that they can spread
out and create a barrier.
The sooner you get the pre-emergent out of the sun and elements, the longer it'll last.
Be careful not to irrigate too excessively, though.
Doing so can dilute the product's effectiveness.
When applying to beds with mulch, be aware that the mulch my hinder the pre-emergent
activity.
For pre-emergents to be effective, they need to reach the surface of the soil.
The deeper the mulch, the more likely the pre-emergent won't be able to reach the soil
and form a complete barrier.
If you do need to treat a mulched area, research has shown that oxadiazon, the active ingredient
in Ronstar, does provide good control in the situation.
The bulk of weed control in beds can be done through pre-emergent herbicides.
However, landscape professionals don't always have the opportunity to apply a pre-emergent
control.
In these situations, they will use a post-emergent to eliminate existing perennial weeds.
Post-emergents will not prevent new weeds from emerging and have no effect on weed germination,
so you may need to make multiple applications during the season.
The biggest advantage of post-emergent herbicides is that you can spot spray with them, rather
than covering the entire bed.
The most common post-emergent herbicide used for weed control in beds is glyphosate, the
active ingredient in Roundup, but there are other non-selective and selective herbicides
to choose from.
To get the best results from your application, keep these tips in mind.
Always read the label and follow the manufacturer's instructions for use.
Monitor your spray pressure, as excess pressure results in misting and drift.
Spray when the air is calm.
In the confines of a planter bed, wind can quickly increase the chance of damage to other
plants.
Lastly, avoid walking through the areas you've just treated, or you risk contaminating other
areas with your shoes.
Now, this is just a general overview of weed control in planter beds.
If you would like to learn more about pre and post-emergent herbicides or other turf
related topics, please attend one of our live education seminars.
For more information, stop into your local Ewing branch, or visit us online at ewingirrigation.com.