Pigweed Control

Identification

Pigweed, also known as redroot amaranth, is a notorious agricultural weed. It is mostly green in color with some reddish streaking in the stems. It is covered with what feels like rough hair. It is grown as a seed crop in some cultures because each plant produces many thousands of seeds.

Pigweed

Pigweed flowers and seeds

Pigweed plant

If you live anywhere near an agricultural area, pasture weeds like pigweed (a.k.a. redroot amaranth or Amaranthus retroflexus) are probably a major problem in your garden—especially if the garden is new. You might notice a red fuzz over the soil in the spring. Upon closer inspection you realize the ground is covered with billions of germinating amaranth seeds. Not all of those seeds will grow into mature plants, but even if a few are allowed to go to seed, they can potentially make millions of more seeds to infest your garden long into the future. So you see why the control of pigweed is so important—we are at war and the weed is winning.

Controlling Pigweed

Cultivate your garden soil. If you are starting your garden in the spring and there are a million little pigweed seedlings sprouting up, running your tiller over them will kill almost all of them very easily. You can do the same thing more accurately and more gingerly with a hoe or a small-forked cultivating tool. As the plants get bigger it becomes more important to ensure that they are upturned, roots exposed, or there is a chance they could reemerge (and you'll double your work).

Apply a preemergent. The thing with new gardens or gardens that have been allowed to lay fallow is that there can be millions of seeds within a couple square yards. Even if you are diligent about cultivating and turning over soil that has sprouted, you will likely just be bringing new seeds to the surface. This is why applying any preemergent product in the area you tilled might be a good idea. Take care that it isn't an area of your garden in which you intend to plant seeds any time soon. Adult garden plants should be unaffected as long as they aren't exposed directly.

Mulch weedy areas. If your garden is small enough or if you can manage it, mulching between your garden plants is a wonderful way to prevent pigweed from making an appearance. There are lots of options for organic mulches. Composted manure and animal bedding works great, as does bagged grass and leaf clippings from your mower. If the grass was longer or contained dandelions, be careful of the seeds. Composting the seedy mulch for a season will take care of that. Shredded straw bales are another cheap mulch that can help prevent weeds. There are a bunch of wood-based mulches commercially available that can work, but often their purposes are more decorative.

Kill it with plastic. This method is technically another type of mulch in that it suffocates the weeds. The first step is to go over the area you want to cover and pick out any sharp rocks or sticks. Then rake it smooth. Decide which areas are going to be your planting areas and which areas will be mulched with plastic. Lay down your drip hose if you are using one. Choose a calm day to lay down your plastic and keep it flush with the ground. Add rocks to hold it in place as you go. You can also stake the plastic or partially cover it with soil or organic mulch to secure it. Cut out holes for planting areas and you're set.

Manually remove plants. If it comes down to it and you've missed your chance to apply a preemergent herbicide, you didn't do a very good job of cultivating the soil when the weeds were small, your mulching skills were lacking, or your plastic cover blew away in a windstorm, then I'm afraid you're just going to have to bend over and pull that weed up with your hands. It is especially important that you do this before it goes to seed or you are shooting yourself in the foot for many years to come. Sometimes pigweed can have a deep taproot, so you might need a shovel to dig down and remove that thing—an ax might also be helpful.

Pigweed Herbicides

Depending on where you live, some wild pigweeds have been found to be resistant to agricultural herbicides like Roundup and Atrazine. This is a real problem for people who grow crops for a living, as it can affect their ability to make a profit. This isn't going to make that much of a difference for home gardens because you should be able to use another control method fairly simply. If you still want to use an herbicide, any broad-leaf herbicide should work assuming there is no resistance. One could worry about contributing to the problem of creating more resistant amaranth, but when you consider how many hundred million pounds of herbicides are spread on fields in the Midwest every year, the problem is way beyond the scope of the home user.

Natural Pigweed Control

Cover crops. One way to combat weeds like redroot amaranth is to plant a cover crop. There are a lot of plants that can fill that role. The main thing is that they need to be able to grow close to one another and thus choke out all competition. Grains like oats, and greens like lettuce, chard, and spinach will all make a stand against pigweed (with a little help from you).

Corn gluten. Corn gluten is a by-product of corn processing that has been shown to prevent seeds from sprouting. Corn gluten is non-toxic and biodegradable and acts as a preemergent herbicide when applied in the spring.

Vinegar. Plants require a certain pH level to live comfortably. If it's too high or too low, the plant will weaken or die. One cheap and widely available source of acid is the white distilled vinegar you can buy in the grocery store. You can use it as an herbicide by spraying it on young pigweed plants, though a stronger acid would be more effective.

Just eat it. Pigweed greens aren't suggested as a forage crop for livestock because of the large amount of nitrogen locked in those leaves, but they are completely edible as long as you aren't eating as much as a cow. Cooking them as a leafy green is usually preferable because of the fuzziness. The seeds are very nutritious and can be dried and used as a grain.