How to Use Mulches to Control Weeds on your Garden

Suppressing weeds with a layer of mulches is without a doubt one of the best organic weed control tips out there. But, mulching only works if you do it right.

1. Apply mulch early in the season, before annual weed seeds germinate. If you wait too long, weed seeds with already have germinated and they will grow right up through the layer of mulch.

Don’t mulch until you get rid of all existing weeds first. This means taking the time to pull or otherwise remove any and all weeds, not simply dumping the mulch on top of them.

A layer of mulch doesn’t usually smother existing weeds; they’ll just grow up through it as the season progresses.

2. Only use mulches that are weed free and come from a reliable source, otherwise you could end up introducing more weeds to your garden.

We use commercially produced leaf compost in our vegetable garden and perennial beds, and shredded hardwood bark in my shrub beds.

3. Use straw, not hay, for a mulch. Straw is the dried stems of wheat or other grains and is typically weed free, but hay is mixed forage and often contains many weed seeds.

We love to use straw to mulch the paths of our vegetable garden.

4. Never use treated lawn clippings. While collected grass clippings make a great mulch in the vegetable garden, do not use them if the turf was treated with herbicides or chemical fertilizer products.

5. Don’t over-mulch: No matter what type of mulch you use, two to three inches of it is enough. If you pile too much on, you risk inhibiting air exchange with the soil and the roots of your plants.

Read Also: What is Mulching and Importance of Mulching

Different Types of Mulches for Your Garden

There are two basic kinds of mulch: organic and inorganic. Organic mulches include formerly living material such as chopped leaves, straw, grass clippings, compost, wood chips, shredded bark, sawdust, pine needles, and even paper. Inorganic mulches include black plastic and geotextiles (landscape fabrics).

Both types of mulch discourage weeds, but organic mulches also improve the soil as they decompose. Inorganic mulches don’t break down and enrich the soil, but that doesn’t necessarily mean they’re not a smart option for your garden.

Case in point: Black plastic, a popular kind of inorganic mulch, warms the soil and radiates heat during the night, keeping heat-loving vegetables like eggplant and cherry tomatoes cozy and vigorous.

Here are the six most common types of mulch to choose between:

1. Wood Chips or Shredded Leaves

You can purchase bags of decorative wood chips or shredded bark from a local garden center to mulch your flower garden and shrub borders. For a less expensive option, call your local tree-care or utility company to see if they have any extra wood chips on hand. Or if you’re really planning ahead, chip your Christmas tree instead of tossing it to the curb.

If you have trees on your property, shredding the fallen leaves creates a nutrient-rich mulch at no added cost. You don’t need a special machine either: a lawn mower with a bagger will collect leaves and cut them into the perfect size for mulching.

Spread a wood chip or shredded leaf mulch anywhere on your property, but it looks best in flower beds, shrub borders, and garden pathways. Of course, it’s right at home in a woodland or shade garden.

Keep in mind that wood chips aren’t a smart choice for vegetable and annual flower beds, since they’ll get in the way as you dig the beds each year.

2. Grass Clippings

Grass clippings are another readily available mulch, although it’s a good idea to save a portion of the clippings to use as a natural lawn fertilizer. When you have remaining grass clippings, use them as nitrogen-rich mulch in vegetable gardens.

3. Compost

Give your compost another purpose: If you have extra to spare, use it as mulch. It will enrich the soil and make plants happy, but keep in mind that when any kind of mulch is dry, it’s not a hospitable place for plant roots.

That means, you may want to reserve your compost to spread as a thin layer around plants and top it with another mulch, such as chopped leaves. This allows the compost to stay moist and biologically active, providing maximum benefit for your vegetables, fruits, or flowers.

4. Straw or Hay

If you’re planting a vegetable garden, consider covering it with straw, salt hay, or weed-free hay. Not only does it look clean and crisp, but this type of mulch retains soil moisture, prevents weeds, and adds organic matter to the soil when it breaks down.

Just make sure you opt for a weed and seed-free hay, and avoid piling it around stems of vegetable or fruit tree trunks to prevent slug and rodent damage.

Read Also: Mulching of Plantains and it’s Advantages

5. Plastic Mulch

Mulching a vegetable garden with sheets of black plastic film can do wonders. When it’s spread tightly over a smooth soil surface, black plastic transmits the sun’s heat to the soil beneath, creating a microclimate about three degrees warmer than an unmulched garden.

Because the plastic film remains warm and dry, it protects the fruits of vining crops such as strawberries, melons, and cucumbers from rotting. And, of course, the mulch prevents weed growth and retains soil moisture.

Infrared transmitting (IRT) plastics cost more than standard black plastic, but they can result in even higher yields. These plastics warm the soil as well as clear plastic, but also control weeds as effectively as black plastic.

In raised bed gardens, lay down a sheet of plastic over the entire bed. Bury it at the edges or weigh the plastic down with rocks.

Then punch holes in it with a bulb planter, and fill with plants or seeds. Since water can’t permeate plastic, you can’t rely on rainwater to properly hydrate your plants. Instead, lay soaker hoses or drip hoses on the soil surface before you put down the plastic.

Be careful not to use mulch under shrubs, especially since plastic destroys the shrubs’ long-term health. Because water and air cannot penetrate the plastic, roots grow very close to the soil surface sometimes right beneath the plastic seeking moisture and oxygen.

The shallow roots suffer from lack of oxygen and moisture, and extreme temperature changes. Over time, the plants decline and die.

6. Landscape Fabrics

Geotextiles, also called landscape fabrics, let air and water through to the soil beneath while keeping weeds from coming up. But still, there are some drawbacks: When exposed to light, geotextiles degrade over time. To make them last longer, cover them with a second mulch (they’re ugly, so you’d want to, anyway).

Similar to plastic mulch, keep geotextiles away from shrubs. Shrub roots and weeds grow up into the landscape fabric, which means you’ll have to rip the landscape fabric upon their removal.

How to Properly Apply Mulching

There are two cardinal rules for using mulch to combat weeds. First, lay the mulch down on soil that is already weeded, and second, lay down a thick-enough layer to discourage new weeds from coming up through it.

A four-inch layer of mulch will discourage weeds, although a two-inch layer is usually enough in shady spots. If you know that a garden bed is filled with weed seeds or perennial roots, try a double-mulching technique to prevent a weed explosion. To do so, set plants in place, water them well, spread newspaper, and top it with mulch.

Mulches that also retains moisture (like wood chips) can slow soil warming. In spring, pull mulch away from perennials and bulbs for faster growth. A wet mulch piled against the stems of flowers and vegetables can cause them to rot; keep mulch about one inch away from crowns and stems.

Mulch piled up against woody stems of shrubs and trees can also cause rot and encourages rodents (such as voles and mice) to nest there. Keep deep mulch pulled back about six to 12 inches from trunks.

Read Also: The History and Spread of Cultivated Crops