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https://hgic.clemson.edu/factsheet/controlling-weeds-by-cultivating-mulching/

Controlling Weeds by Cultivating & Mulching

Factsheet | HGIC 1253 | Revised: Sep 1, 2016 | Print

A stirrup hoe can be used to cultivate in-between rows of direct seeded crops.
Zack Snipes, 2020, Clemson Extension

Consider your weed control strategy prior to establishing a vegetable garden in the spring. Weeds compete with vegetables for water, nutrients and light. They also harbor insects and diseases, which may then spread to vegetables. Efforts made early in the growing season will reduce the time required for hand-weeding later in the season. The weed control program may require a combination of methods to manage all weed species.

In a large garden with widely spaced rows, a rotary tiller will make weed control easy and fast.
Barbara H. Smith, 2016, HGIC, Clemson Extension

The most common weeds found in the garden can be divided into summer annuals, winter annuals and perennials. There are a few biennial weeds in South Carolina, but these are generally not a problem in gardens.

Summer Annual Weeds

Summer annuals are weeds that germinate in spring or early summer and flower in the summer or fall. This is the most common type of weed found in the garden. This group can be further divided into summer annual grasses and summer annual broadleaf weeds.

Common summer annual grasses include large crabgrass, goosegrass and giant foxtail. Annual grasses are easy to control if appropriate measures are taken early in the growing season but can quickly become a severe problem if not controlled when small. Large crabgrass, for example, will root into the soil at the places where the nodes of the stem contact soil, allowing this plant to quickly cover open ground. The fibrous root system of grasses makes them more difficult to pull out of the ground.

Common summer annual broadleaf weeds include smooth pigweed, common lambsquarters, purslane, galinsoga, common ragweed and tall morningglory. When controlling purslane through hoeing, remove all stems from the garden because purslane can reroot if allowed to remain on the soil surface due to the thick, succulent stem that can survive a period of drought. Galinsoga is often called quickweed, perhaps because it develops quickly and flowers while still a small plant. It seems that most gardens contain purslane, galinsoga or both. Small-seeded broadleaf weeds like pigweed are easier to control than large-seeded broadleaf weeds like morningglory. Larger-seeded weeds can germinate from a greater soil depth and can push through a shallow layer of mulch.

Winter Annual Weeds

Winter annuals are weeds that germinate in fall and flower in the spring. These weeds are often present at the time the garden soil is prepared in the spring prior to planting. Tilling the soil will kill existing stands of common chickweed and other winter annuals. Annual bluegrass is a common winter annual grass, while henbit, common chickweed and wild mustard are common winter annual broadleaf weeds. Weeds in this category are generally not as troublesome in the garden as summer annuals.

Perennial Weeds

Herbaceous perennial weeds can be especially difficult to manage in a garden. These plants are killed back to the ground by a hard frost and overwinter through underground plant parts, such as tubers or rhizomes. Tilling the garden may spread these weeds by fragmenting and moving root pieces. Each of the root pieces may develop into a complete plant. The most common perennial weeds are common bermudagrass and yellow nutsedge. Bermudagrass, often called wiregrass, spreads by creeping stolons and rhizomes. Thoroughly remove all plant parts from the garden when hand-weeding because bermudagrass can reroot into the soil. Yellow nutsedge is often called nutgrass, but this plant is a member of the sedge and not the grass family. Yellow nutsedge reproduces by underground tubers.

Mulches

Mulches can be divided into organic, such as grass clippings, and inorganic, such as black plastic. Mulches can be the easiest and most effective way to control annual weeds in the garden. Mulches may also suppress perennial weeds. Mulches control weeds by preventing sunlight from reaching the soil surface. Light is required for the germination of certain weeds, and light is required for the growth of all green plants.

Organic Mulches: Organic mulches include grass clippings, pine bark, straw or similar materials (see table, page 3). Organic mulches cool the soil surface, which is beneficial during hot summer days, but may reduce crop growth in the spring. Do not use grass clippings from a lawn that has been treated with a broadleaf herbicide such as 2,4-D. Tomatoes, peppers and most other vegetables are very sensitive to 2,4-D and could absorb residues of the compound from the treated grass clippings.

Avoid over mulching, which can reduce oxygen levels in the soil. Crop roots require oxygen for growth, so limit the mulch layer to a maximum of about 3 inches. Organic mulches provide good control of annual weeds, but perennial weeds may be able to push through the mulch layer. Also, annual weeds may germinate and grow in the mulch layer.

When using an organic mulch, make sure that the source is not contaminated with weed seed, rhizomes or tubers. Weeds are often spread by contaminated mulch, making weed control harder than if no mulch was used.

https://scotts.com/en-us/how-to/how-to-control-weeds-naturally-with-mulch.html
How to Use Mulch to Keep Weeds out

Weeds need light and warm soil to survive. To use mulch as a natural weed barrier, you need to put down a 2- to 3-inch layer. That's enough to keep most weed seeds from sprouting. Because you block their access to sunlight, they won't have enough energy to push through the mulch.

Control Weeds Naturally

Weeds are a nuisance, ugly, and can even be invasive. They steal water and nutrients from the plants you love. If you pull them out, they often grow right back. They hog the sun, and act like garden bullies. Even so, you can't bring yourself to spray them into oblivion with week killers. So, how do you naturally help keep them out of your garden? Simple. With mulch.

What Kind of Mulch to Use

Different mulches have different uses. Pebbles and small stones can be considered mulch, but don't break down and amend the soil. Straw is often used in vegetable gardens, but it tends to contain many weed seeds. Grass clippings are also popular, but they lack aesthetic appeal. Your best bet is bark mulch, such asScotts Nature Scapes Color Enhanced Mulch orScotts Nature Scapes Triple Shred Mulch. It gives your garden a clean, finished look while holding down weeds. Also, since it's a natural product, it amends your soil as it breaks down over time.

Mulching around your Garden

If you have a bed of perennials, wait until the flowers push through, then lay down a 2- to 3-inch layer of mulch all around them. When planting annual flowers, plant them first and then mulch the surrounding area. If you're mulching around trees, shrubs or roses, avoid piling the mulch against the bases of the trunks and stems. Because Scotts Nature Scapes Mulches are a natural wood product that breaks down over time, you will need to replenish the mulch annually to maintain a 2- to 3-inch layer.