GoodSeed Farm > Weeds - Prevention & Control

Weeds - Prevention & Control


Gardening is much easier if you take steps early in the season to control weeds in your garden or landscape beds. This is a hot topic with us since we all hate to pull weeds, particularly in the summer when we’d rather relax in the shade. It helps to understand a few things about weeds. 

There are basically three kinds of weeds: Annual weeds that sprout from seed each year, and biennial and perennial weeds that are growing already. Crabgrass is a good example of an annual weed. Since weed seeds won’t sprout in complete darkness, mulching your garden early in the season (or anytime the ground is disturbed) will prevent most annual weeds by preventing the sunlight from reaching the weed seeds in your soil. More and thicker mulch does this better, skimpy mulching helps but not as much. Once mulch is down, avoid sweeping or blowing dirt or clippings onto it. 

Annual and biennial weeds may already have roots established, and they can fight their way through mulch and come up anyway. Thistle and ironweed are good examples of perennial weeds. Wild onion and dandelion are biennial weeds. Mulching helps prevent them from sprouting from seed, but existing weed plants must be dug out or killed. 

Before making new beds we like to apply Roundup to kill the existing grasses and weeds. This saves a lot of work later, because tilling perennial weeds just spreads them around. Putting down weed barrier fabric under your mulch helps prevent perennial weeds from taking over your beds, but makes it harder to till and plant them later. 

Chemical weed control has two steps: Pre-emergent control (preventing weed seeds from sprouting) and post-emergent control (killing weed plants that are already growing). Most pre-emergent weed products (like Preen) are based on the same active ingredient: Treflan. Treflan forms an invisible barrier that kills annual weeds just after they sprout from seed. OSU studies show that Treflan works best when it’s mixed into the top ¼ inch of soil or mulch.  

This is why the best way to apply Treflan is in liquid form, soaking it into the mulch right after you spread it. If the mulch is disturbed later you’ll need to reapply. Our favorite pre-emergent is Monterey “Weed Impede Hose-Em” in hose-end sprayer packaging. This works far better than powdered Preen and is easier to use (and cheaper since there’s no “filler”). Just screw the bottle of concentrate to the end of a hose and spray. 

Killing established weeds in garden beds with a chemical like Roundup is usually more effective than trying to pull them. It’s hard to get all the roots, and when you do you’ll scatter soil on top of your mulch, leading to more weeds. The active ingredient in Roundup is Glyphosate, which kills by being absorbed into leaves and traveling down to the root system. It takes about a week, and the weed needs to be actively growing for it to work. Glyphosate doesn’t linger in the soil and won’t kill anything unless it’s applied to the leaves or stems. Using a pump sprayer works well for applying Glyphosate products as long as there’s no wind to cause spray drift onto other plants. 

When buying Roundup or other Glyphosate products, pay attention to the label where it says “active ingredients”. Often the product is mostly water, with as little as 2% Glyphosate. The stronger the concentration the more effective it will be. We like Remuda concentrate (41% Glyphosate) because we can dilute it to whatever strength we need; stronger for brush or woody plants like Poison Ivy or weak for annual weeds in the vegetable garden. Painting Remuda full-strength on the cut-off stumps will kill locust, mulberry or other nuisance woody plants. 

Here’s a trick for killing weeds among other plants without harming them: we call it the “Roundup Glove”. Wear a cotton glove over a rubber glove. Mix up Roundup (or Remuda) in a small bucket or pail. Dip your gloved fingers in the solution and then wet the weeds with the soaked glove. Everything you touch will die, and the plants around it will be fine. No spray drift to worry about.