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Garden Help Desk: What’s the best way to get rid of weeds?

By USU Extension - | Jun 18, 2022

Courtesy photo

Regular mowing, an important part of good lawn care, can slow down the growth of some weeds. When lawns and weeds are ignored, the problem will only get worse.

I was told that if you want to get rid of weeds in your lawn, scrape the existing lawn off. Then put weed barrier down, put 3 inches of topsoil on top of the weed barrier. Then sod on top of that. Will that work?

No. That will just give you an unhealthy lawn. A 3-inch root zone is nowhere near enough rooting depth for a healthy lawn. Some lawns squeak by with just 4-to-5-inches of good root zone, but a 6-to-8-inch root zone is a better goal. Not only will you have a lawn that struggles and needs extra attention, you’ll also still have weeds.

Weeds get into lawns when seeds get into the lawn, so underlaying your lawn with weed barrier won’t stop weeds from showing up; the seeds will float in on a breeze, be tracked in on shoes, blown in by winds, and dropped in by birds and other critter. It’s true there are some weeds that develop underground rhizomes (runners) once their seeds get into the lawn but using weed barrier won’t stop them from getting back up into the lawn either, as they easily find their way between the overlapping edges of the weed barrier.

Think through the project you’re considering. Removing your existing lawn, plus several inches of soil so that you can lay weed barrier and top that with topsoil, would be a lot of work. That’s a lot of hard work, but the project would also be expensive. You’d save some money by putting back the soil you removed instead of buying new topsoil, but a project like this always includes surprise expenses. Considering all the work and expense for a project that ultimately wouldn’t give you the weed-free lawn you hope for, I think you’d be happier using more convention weed-control methods for your lawn.

There’s a better, more reliable way to manage weeds in lawns — good lawn care. A healthy, dense lawn makes it difficult for weeds to get established. Good lawn care includes:

  • Applying adequate fertilizer (usually just nitrogen, and not too much)
  • Watering deeply, but not frequently, to promote a robust root system
  • Mowing taller (3-3.5 inches) to shade weed seeds
  • Using a mulching mower, if possible, to “smother” any eager weed seeds that want to germinate
  • Use organic or conventional herbicides if you have stubborn weeds in your lawn. Both pre-emergent products and post-emergent products can be helpful.

Courtesy photo

Unhealthy lawns thin out easily, compete poorly and make it possible for weeds to establish and spread easily. Good, routine lawn care can prevent many weed problems.

I’m going to start using mulch in my garden and flower beds what is the best kind?

There are lots of options when it comes to choosing mulch for a garden, flower bed or shrub bed. Each kind of mulch has its pros and cons. The best mulch for you depends on where you’re using it and what you expect the mulch to do for you.

Black plastic is a common mulch choice in vegetable gardens

Advantages — It helps warm up the soil in the spring, conserves moisture and helps to reduce weeds.

Disadvantages — it needs to be removed at the end of the season, it needs to be disposed of once it’s worn out, and it doesn’t do anything to improve the quality and structure of your soil.

Courtesy photo

Whenever weeds get a chance to bloom, they can drop seeds, making it easy for the weeds to spread.

Grass clippings are readily available for many gardeners.

Advantages — they’re a no-cost option, they can add organic matter to the soil, can help to cool the soil during the summer, can keep down weeds and conserve moisture.

Disadvantages — must be added in thin layers, week-by-week; can’t be used for a couple of mowings after the lawn has been treated with a weed killer, will become a slimy mat if applied to thickly before it’s dry.

Shredded leaves saved from autumn collecting.

Advantages — good for flower beds and shrub beds, helps to improve the soil, conserves moisture, can help to cool the soil during the summer, and controls weeds when applied properly.

Disadvantages — can be expensive if used in large areas, needs to be topped off every few years.

Compost can be used as a 1-1.5″ mulch layer, in addition to being used as a soil amendment.

Advantages — good for vegetable gardens and annual flower beds, good for weed control, conserves moisture, can help to cool the soil during the summer, improves soil quality, can be turned under or simply left in place at the end of the season.

Disadvantages — only lasts for one year, so must be replaced annually, not decorative.

Gravel, pebbles, and river stones are becoming more popular.

Advantages — doesn’t break down, so doesn’t need replacement every few years; stays put, if properly installed.

Disadvantages — doesn’t improve the soil, can heat up during the day and stay hot into the night, can reflect heat up onto trees and shrubs and keep soil too warm in the summer, contributing to plant stress; is very difficult to remove when new plantings are needed, so should be considered permanent.

Newspaper and shredded office paper are very economical.

Advantages — free, conserve moisture, helps to keep soil cool during the summer, and controls weeds.

Disadvantages — not attractive, can be blown out of place if not weighed down.

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