A website from UGA Cooperative Extension

What makes a weed? – Jessica Warren, ANR Agent Camden County

What is a weed? Much like beauty, a weed is in the eye of the beholder. The definition of a weed is any plant that is growing where you don’t want it. Today I’ll discuss the characteristics of weeds, uses and benefits of some of them, ones to really watch out for, and what your weeds might be telling you about your landscaping practices.

There are some characteristics that plants that are considered weedy share. Weedy plants tend to produce lots of seed — sometimes tens of thousands of seeds per plant. Their seed can often survive for a long time in the soil, staying dormant but then sprouting just as soon as conditions are right. Sometimes mildly disturbing the soil is often enough to trigger new growth. Weedy plants are able to establish themselves quickly. Sometimes they seem to pop up overnight (especially in rainy weather). Weedy plants often have mechanisms that enable them to spread easily, such as the ability to reproduce vegetatively without seeds. They can grow in inhospitable environments where more desirable plants typically wouldn’t survive.

Often your weeds are telling you something about your landscape, or your landscape management habits. Red sorrel prefers soil with a low (acidic) pH. You can raise the pH of your soil by adding liming materials as directed by a soil test. Add lime with caution; it is very difficult to lower the pH of your soil if you accidentally raise it too high. Alternatively, you can install plants which prefer acidic soil, like blackberries, gardenias, azaleas, and blueberries. Broadleaf plantain, on the other hand, prefers soil with a high (alkaline) pH. Unlike raising pH, lowering the pH of soil is very difficult, even impossible. Many of Georgia’s soils are formed from calcium-containing materials like limestone, which keep the pH high. Routine applications of amendments with elemental sulfur or organic material should lower the pH for a time, but repeated application will be necessary. Instead, I suggest embracing your alkaline soil and choosing plants that prefer a high pH environment. Clovers and other legumes are often an indication of soil with low nitrogen. These plants fix nitrogen in their roots, making them less dependent on the soil’s available nitrogen and the last survivors in a nitrogen-poor landscape. Because nitrogen levels change rapidly, soil tests don’t normally report nitrogen levels. A good soil test report will include nitrogen application rates for turf and ornamentals, so it is still recommended if you suspect low nitrogen. Add nitrogen to your soil responsibly by following recommended nitrogen fertilizer rates. This will help to prevent plant injury and to protect water quality. Too much nitrogen can be damaging to your landscape and the environment. Annual bluegrass and chickweed are winter weeds that are symptoms of a lawn regularly mown too low. Check the recommended mowing height for your turfgrass. You should also avoid removing more than a third of the blade at one time, so don’t let the grass get too long between mowings. Healthy turf will fight off these weeds with ease. Goosegrass, also called silver crabgrass or crowfoot, is a turfgrass weed that thrives in compacted and wet soils. Soil compaction is usually the result of heavy foot or vehicle traffic and is common in newly constructed homes. Loosen soil with a hoe, pitchfork, or tiller and consider adding organic matter before landscaping. Aerating your lawn can also help correct soil compaction in high traffic areas. If you’re repeatedly walking or driving over the same part of your landscape, install mulch or permeable pavers to serve as paths or driveways. Sedges, doveweed, dollarweed, and eclipta all prefer soggy, wet soil. It is possible that your landscape is overwatered, but these plants may also be a sign of leaks in your irrigation system or of poor drainage. You can also embrace the sogginess and turn the area into a rain garden.

As discussed in a previous article on edible landscaping, many of the plants that we often consider weeds are edible and quite tasty and nutritious. This includes greenbriar species, dandelion, Florida betony, dollarweed, purslane, yellow nutsedge, common blue violet, sheep’s sorrel, Asiatic hawksbeard, and Virginia spiderwort. As always, never consume any plant without doing your own research using credible sources and being 100% confident in your plant identification skills. Do not consume any plant that has been treated with lawn or landscape pesticides as these are not usually safe for use on food plants.  

Another benefit of many “weeds” is their use as wildflowers – for aesthetics, for pollinators and beneficial insects, and for wildlife. Many “weeds” are actually native wildflowers that are resilient in the landscape and valuable in the ecosystem. These wild plants are often important nectar and host plants for native pollinators and other insects. Most flowering plants provide pollen and/or nectar resources to pollinators and other wildlife – including other insects that form the base of the foodchain. Weeds can also provide shelter, forage and nesting materials for various insects and wildlife. I always like to say, one man’s weed is another man’s wildflower.

While there are weeds with great benefits, there are also weeds that do great harm. Invasive plants are truly weeds whether they are plants that we typically think of as weeds or not. Invasive plants are non-native plants that displace native plants, reproduce prolifically, and cause environmental and/or economic harm. Among these are vinca, chinaberry, camphor tree, Chinese tallow, asparagus fern, sweet autumn clematis, pampas grass, liriope, mimosa tree, Japanese honeysuckle, nandina, lantana, air potato, wisteria, wild taro (elephant ear), Mexican petunia, sword fern, coral ardisia, and English ivy.

If you’re someone who follows landscape trends you may know that monoculture lawns are quickly falling out of favor across the country (and the world). Lawns are being minimized for flowering, often native, plants, and the mowable areas are incorporating more species than just one turfgrass species. There are many reasons for this from building pollinator and wildlife habitat, to reducing pollution, expense, and labor. Ecologically, the traditional lawn is a dead zone that is not conducive to butterflies, bees, or any other lifeform. We know that monoculture lawns are impractical and unsustainable, but what if we take the good in a lawn and toss out the parts that contribute to waste? What if we use our lawns and weeds to build habitat and reduce our labor and expense? Other plants and “weeds” can fill in the gaps where turfgrasses struggle, preventing soil erosion and water pollution. This builds a resilient and low-maintenance lawn that doesn’t require pesticides – making it safer for people, pets, and pollinators. For years I’ve promoted this idea to clients that are open to it, calling it a biodiverse lawn. I was very excited to recently read an article out of the University of Florida promoting the same concept but coining it “mixed mowable species lawns.” Benefits of a mixed mowable species lawn include increasing the overall turf quality under drought, increased carbon sequestration, decreased non-point source water pollution due to minimal to non-existent fertilizer needs, better performance in problem areas, water conservation, species diversity, habit for beneficial insects, savings in time and money (due to eliminating the need for fertilizers and various pesticides), flowers that increase aesthetic value while attracting and supporting pollinators including butterflies, and added nitrogen to the soil through the use of legume species. Some mixed mowable species to consider are creeping beggarweed, southern pencil flower, clover species, Florida pusley, turkey tangle frog fruit, crabgrass, sedges, spurges, sorrel, purslane, powderpuff, and blue-eyed grass. Many of these species may already be in your lawn if they are allowed to grow where the turfgrass is struggling.

I realize that the ideas that I’ve proposed in this article will seem radical to some of my readers, and you may not be prepared for this kind of change. Don’t worry, I have something for you too. If weeds are, and will always be, your nemesis, here’s some advice for you. If you are treating the weeds in your landscape, it’s important to know what you have and the appropriate treatment. Herbicides have different efficacies against different weeds and may be safe for use in/near some turf or ornamentals but not others. Your local extension agent can identify your weeds and make a treatment recommendation based on where it is growing. The safest solution for you, your desired plants, pets, children and the environment is, and will always be, to pull your weeds. Keep in mind that it is illegal (and dangerous) to use any pesticide differently than the label directs. The best defense against weeds is a healthy lawn. Healthy turf blocks sunlight from reaching the soil – preventing weed seed germination and limits the physical space for weeds to occupy. Proper turfgrass selection is critical – consider pH, nutrient, and light requirements before planting. If turf is over- or underwatered, over- or underfertilized, or mowed too low or too infrequently, the turf is weakened and weeds move in. Many annual weeds can be eliminated if proper mowing height and frequency are maintained. Mowing prior to weed seedhead formation also reduces weed seed reserves. As a rule of thumb, when mowing, remove only a third of the turf’s leaf blade at a time. This maintains a turf canopy that can grow vigorously while shading weeds and suppressing their growth. Sharpening the mower blades can reduce turf damage and the chances for weed invasion. It is very important to understand that weeds don’t create a void; they fill a void.

Ralph Waldo Emerson described a weed as a plant whose virtue has not yet been discovered. He may have been on to something.