What Is Pigweed and How Do I Get Rid of It?

No one is 100 percent sure, but pigweed may have gotten its name because it was once used as food for pigs. In some places, this weed—also known as amaranth—has served as an important source of nutrition for people. But if you spot this common weed growing in your garden or lawn, you probably just want to learn how to kill it effectively and get rid of it for good.

Here’s what you need to know.

What is Pigweed and Why Is It a Problem?

Pigweed is just that—a weed. Yet that doesn’t tell the entire story.

Did you know there are different types of pigweed? They’re all classified under the species Amaranthus, but that’s where the similarities end. Amaranthus blitoides, AKA prostrate pigweed, is the one we’ll focus on here. It’s the one that shows up in your garden or hides in your lawn.

Prostrate pigweed—AKA mat amaranth, prostrate amaranth or spreading pigweed—is a summer annual that acts like a perennial. Although it completes its life cycle in one growing season, it can come back year after year, seemingly resisting any attempts to eradicate it.

That’s because, in any given year, it produces and disseminates more than 100,000 small black seeds that look like tiny grains of sand. These seeds can lie in the soil dormant for up to 20 years before randomly germinating into problematic weeds when conditions are just right.

Why do lawns get pigweed?

All weeds are opportunistic. If there’s a “crack in the door,” they’ll enter. Lawns that lack turf density have exposed ground where weeds, like prostrate pigweed, can get a foothold.

Like most lawn weeds, the presence of pigweed indicates your lawn lacks something. You can improve lawn health by fertilizing and maintaining proper soil moisture.

How to Identify Pigweed in Your Garden or Field

This lawn and garden adversary is a low-growing plant with alternate, pale-to-shiny dark-green leaves that are oblong to egg-shaped. These leaves can be pointed or rounded to some extent and have a slightly indented leaf tip.

The light green to reddish plant stems hug the ground. Often, they form thick, circular mats via one- to three-foot-long stems when allowed to mature. If you look closely, you may find small, greenish flowers in dense clusters at the leaf axil, where the leaf meets the plant stem.

Types of pigweed

Pigweed species can be difficult to distinguish from each other. However, being able to identify pigweed is key to choosing the right control methods and protecting your garden from it.

• Prostrate pigweed, the one in focus here, hugs the ground and spreads in a circular or star-like pattern, often forming thick mats. This aggressive, low-growing weed can overrun lawns and gardens if not eradicated.
• Rough pigweed (Amaranthus retroflexus), also known as redroot pigweed, redroot amaranth, careless weed or wild beet can be found throughout North America. Surprisingly, besides being an agricultural nuisance, it has a few delightful culinary attributes, which we’ll touch on below.
• Waterhemp and Palmer amaranth are also classified as pigweeds but are not considered a problem in home lawns and gardens. Reaching a towering height of three to eight feet, they are most often found in agricultural crops and along fence lines.

Effective Methods To Kill Pigweed

Manual removal:

Start with the old-fashioned way: Hand-pulling the weeds can be arduous, but it provides the best results and is environmentally friendly and chemical-free. Smaller plants are easier to pull. To make the job easier, water the area first to soften the ground and get as much of the root as you can. And if you compost, throw the pulled weeds into the bin—but only if they haven’t gone to seed.

Pre-emergent herbicide and post-emergent herbicide:

Most conventional broadleaf herbicides will do an effective job. Of course, when using any pesticides, always follow the directions on the product label.

Because pigweed is an annual, it can be effectively controlled with a pre-emergent herbicide in the spring. The same one you use for crabgrass control can help prevent pigweed from sprouting in your lawn. Combination products of pre- and post-emergent herbicides prevent new pigweed plants from germinating and control existing weeds in a single application. You can also use nonselective herbicides containing glufosinate.

Note: Remember, they will kill everything you spray, including your lawn. Be careful!

Preventing Pigweed from Growing Back

Mulching: Apply 2-3 inches of organic mulch, such as compost, shredded bark or hay. This acts as a physical barrier over the soil that blocks sunlight and helps suppress pigweed seed germination.

Soil management: Pigweed thrives in poor, compacted, nutrient-deficient soil. Maintain healthy soil with proper pH and nutrient levels to promote dense turf and reduce space for weeds.

Regular monitoring: Pigweed is a fast grower, going from seedling to seed-producing in just a few weeks. Inspecting your garden thoroughly, especially during warm weather, is essential to catch and remove pigweed early.

Avoid soil disturbance: Seeds can remain dormant for many years. Every time you till or dig the soil, you risk bringing those seeds to the surface where they can germinate. This is especially important in fields or garden beds with known pigweed history.

Crop Rotation: Seasonal rotation of crops disrupts pigweed’s growth cycle, making it more difficult for it to adapt to and dominate the same location year after year. Plants such as corn or soybeans that grow in warmer months should be rotated with cooler-season cereals to help block the pigweed germination window.

Cover cropping: Another potent strategy to deal with pigweed is cover cropping. Seeding close-spaced, rapidly growing cover crops like cereal rye, clover or alfalfa shades out the soil surface, depriving pigweed seedlings of the light they require to germinate. The crops compete fiercely for water and nutrients as well, further inhibiting pigweed growth.

Timely mowing: In pastures, orchards and large fields, timely mowing is essential. Pre-flower mowing of pigweed prevents it from flowering and producing seeds, thereby significantly reducing the possibility of future infestations. Preferably, mow when the plants are shorter than 12 inches tall and seed heads have not yet developed.

Tillage timing: When tillage is incorporated in your management plan, timing is everything. Early spring shallow tillage may dry out young pigweed seedlings exposed to air and sunlight before they establish a deeper root system. Frequent deep tillage, however, can dislodge dormant seeds and move them closer to the surface, where they will germinate more readily.

Are There Benefits to Pigweed?

For those who enjoy foraging for natural foods, pigweed can offer some great opportunities. Almost every part of a pigweed plant is edible. Leaves can be eaten raw as part of a healthy salad, or cooked like spinach and eaten as a vegetable. Pigweed greens are rich in iron, calcium, niacin as well as vitamins A and C.

Pigweed seeds, which contain vitamins A and C plus calcium, can be eaten raw or cooked as a hot cereal. They can also be ground into flour for baking and popped like popcorn for a snack.

Note: Always wash collected plants thoroughly before consuming them in case they were treated with chemicals.

FAQ

Is pigweed poisonous?

Pigweed toxicity is not immediate, and pigs may not show clinical symptoms until about a week after ingesting the plant. About half the exposed animals may be affected, though fatalities are generally low. Pigweed can contain significant levels of nitrate and oxalate, up to 30% or more in the form of oxalic acid.

How common is pigweed?

In the Pacific Northwest (PNW) region of the United States, several pigweed species are prevalent and widely distributed. These include redroot pigweed (Amaranthus retroflexus), Powell’s amaranth (Amaranthus powellii), prostrate pigweed (Amaranthus blitoides), and tumble pigweed (Amaranthus albus).

Sources

• Michigan State University: “Prostrate pigweed–Amaranthus blitoides”
• Cornell CALS: “How to identify pigweeds”