July is for water parks and fireworks. And summer weeds.
Spring beds, once freshly mulched, are now struggling to keep out the green invaders.
The simplest definition of a weed is a plant growing where you don’t want it. Depending on when and where the unwanted plant is growing, there are a variety of solutions.
An annual weed germinates and dies in one growing season. To come back the following year, it produces significant amounts of seed in hopes some will find the right conditions to germinate.
Annual weeds such as chamberbitter and henbit are shallow rooted and easy to pull, burn or spray, but there tends to be a lot of them.
A perennial weed produces seed that will germinate, but it primarily reproduces vegetatively via tubers or roots. Pulling perennial weeds such as dollarweed and Florida betony are short-term solutions at best.
Pre-emergent herbicides, such as Dimension or Halts, kill weed seeds as they germinate and are only effective on annual weeds that depend on seeds to reproduce. Post-emergent herbicides, such as Roundup, kill weeds that are already established. They are effective on annual and perennial weeds.
Organic post-emergents such as vinegar and essential oils are only effective against annual weeds since perennials will grow back.
Grassy weeds are grasses. Broadleaf weeds have broad leaves. Those are horrible definitions, but they cut to the chase. I could say grassy weeds are monocots and broadleaves are dicots but that probably wouldn’t mean much to you. However, it does mean they have distinct biochemical differences that can be distinguished by selective herbicides.
Broadleaf herbicides, such as Speedzone and Three-way, are products that will selectively kill broadleaf weeds only. Grassy herbicides, such as Vantage, will only control grassy weeds.
There are several weed control options besides herbicides. In beds, mulch should be kept four inches deep. This is especially effective against annual weeds.
Additional weed control can be obtained with a weed barrier under mulch. This is a physical barrier that blocks annual and perennial weeds. Be sure to use a porous product such as non-woven fabric or newspaper. Avoid plastic. A weed barrier will be effective for three to five years, after which weeds grow on top of it or, in the case of nutsedge, puncture through it.
Competitive plantings smother weeds. Proper spacing of shrubs will fill an area over several years. Groundcovers such as Algerian ivy can monopolize open bed space in a few years and reduce weed pressure as well as mulching needs.
If herbicides are needed in beds, non-selective herbicides such as Roundup are effective on annual and perennial weeds. Weeds absorb the herbicide through the leaves, so only spray what needs to be controlled.
Keeping lawns dense and vigorous leaves little room for crabgrass in the summer. Zoysia is especially effective due to its dense growth habit. Mow lawns as high as possible.
Broadleaf weeds, both annual and perennial, are the main problem in lawns and can be controlled with selective herbicides such as Speedzone and Weed-B-Gone. Grassy weeds are a bit more difficult to control since they also are a grass. Bahiagrass, also called peacegrass due to the peace sign seedhead, is a perennial lawn weed. However, Vantage is a selective post-emergent herbicide that will control it in centipede grass lawns.
There are two weed seasons in the Lowcountry: winter and summer. Crabgrass is the major lawn weed in the summer. Annual bluegrass is predominate in the winter. Both are annual weeds.
Pre-emergent herbicides may not be necessary in competitive lawns. Save your money and time if this is the case. However, if needed, a pre-emergent herbicide should be applied on Valentine’s Day for summer weeds and early October for winter weeds. Another application may be necessary two months later.
Avoid weed-and-feed products at this time. This is combination of fertilizer and herbicide. Lawns should not be fertilized with nitrogen until late April and not at all after August.
Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, e-mail him at tony. firstname.lastname@example.org.