Garden Bed Weed Control Tips

Q: What are the best ways to control weeds in planting beds?

A: Controlling weeds in planting beds is a problem as old as gardening. Here are some tips that will help: 

Remove All Existing Weeds

Start with a weed-free planting area by spraying weed killer or manually pulling or tilling.

Add Organic Mulch

Mulch is good way to suppress weeds, retain moisture, and add organic material to the soil. Although mulch is now often used as a landscape feature, this is not it’s original horticultural purpose.

Weed barriers or fabrics under mulch is NEVER recommended. As mentioned above, mulch adds organic matter to the soil and decomposes over time, becoming compost and rendering the weed barrier ineffective as weeds will now grow on top of the fabric in the fresh soil. 

Keeping a two to three inch layer of mulch is adequate to suppress weed growth. After years of mulching there may come a time the layer of mulch has built up and needs to be removed prior to adding more. 

Consider Chemical Treatments

Chemical treatments can also be a useful tool in fighting weeds. There are two classes of chemical controls: pre-emergent and post-emergent. 

Pre-emergent Chemicals

Pre-emergent chemicals are used to suppress seed germination and have little effect on growing plant materials. This means if a weed has been cut off and the root is in the ground the pre-emergent will not be effective. 

However, saying “pre-emergents have little effect on growing plant materials,” is not an absolute statement. You need to read the label of any product you intend to use to check its effect on any sensitive plants you may have in your garden. 

Common pre-emergents are products like Preen, Preen Extended Control, Treflan, and others. ALWAYS READ THE LABEL. Most pre-emergent herbicides are photodegradable and must be “watered in” using a ½” of water to activate and move them down in order to bond with the soil where they do their work. 

The best time to apply a pre-emergent is early in the spring before any growth has occurred. A follow up application may be required, but as always, read the label for the answer. Are you noticing a theme regarding reading the labels on chemicals?

Post-emergent Herbicides

Post-emergent herbicides are the most common products you’ll find on retailers’ shelves. CAUTION AND CARE must be taken when you make your choices. Some products treat the plant (foliar uptake), and some products treat the soil. 

When using around desired plants be sure they are NOT soil treatments or soil uptake products, and that they have no lingering effects. This will cause problems. 

How do you know how a chemical works? That’s right, read the label. When applying near existing plants, care must be taken to only apply the chemical to the weed and not the desirable plant. There are three common ways to fail while applying post-emergent herbicides:

1.The first way to fail is drift. Wind is a frequent cause of drift. There are few days of no wind so let’s talk about how to spray in light (less than 15 mph) of wind. 

High pressure and small droplets of spray are a recipe for drift. Even with a hand trigger sprayer (like many cleaning products have) the pressure and droplet size are enough for drift. 

A tank sprayer with just enough pressure to get the product to flow out of the wand is best. Another method of application could be using a foam paint brush of the diluted chemical to apply directly to the target plant. This is particularly useful when the weed is close to desirable plants. 

2.The second way to fail applying post-emergents is over application. This can happen by mixing more than recommended and/or by soaking or drenching the weed with chemicals. 

When spraying weeds all that is required is just that, a spray. Depending on the weed and size, only a few drops are needed to control a weed. 

3.The third way to fail is volatilization. Volatilization is when products are applied when there are high temperatures and the product evaporates before it dries. This can be caused by even the slightest air movement. 

You’ve probably experienced volatilization when putting gas in your car. You haven’t spilled a drop, but you still smell gas. Different products will undergo volatilization with different conditions. The best practice is to not apply products when temperatures are high. Eighty degrees Fahrenheit should be the maximum, but the lower the better. 

Glyphosate is the most common herbicide used in this application. While there are many manufactures that sell Glyphosate in their products, Roundup is the most common. Read the active ingredients on the label. The single active ingredient should be Glyphosate.   

Glyphosate has a wide range of control and only kills what it touches. This is why we went to great lengths to describe application methods to target weeds that are a problem. 

Please remember chemicals/herbicides are tools and like many tools they can be dangerous. Always read and follow chemical labels. It’s the law, and it will give you directions for safe, effective use.

Grow Plants to Prevent Weeds

Our final method of bed weed control is to have a thick healthy mass of plant material. Weeds seldomly grow through plants. Letting your plants mass together is not only a better use of your plants to fulfill your design intent, but it also helps with weed control.

Remember, even with best practices there is never a guarantee that there will never be weed problems. Weeds are persistent. The most important thing is to monitor your planting beds regularly, and act with an appropriate control method as soon as the problem occurs.   

Good luck!