Weeds in South Florida all have one thing in common: They are all considered warm-season plants. Unlike warm-season plants that die off or at least go dormant in the winter, the cool season in South Florida may not kill them and, in some years, may not even do much to stunt their growth. Understanding the nature of these weeds, identifying them and ridding your South Florida lawn of them may, therefore, be harder.
Basically, two types of weeds infect South Florida lawns: broadleaf plants and undesirable grasses. Killing them requires different strategies, or you may hurt your entire lawn. In most cases, broadleaf herbicides leave grass unharmed and kill the target weeds, but broadleaf weeds are sometimes resistant to herbicides. Conversely, if you have a problem with grassy weeds, then you may have a more difficult challenge to eliminate them.
Determining a grass weed from a broadleaf weed is generally not too difficult. Typically, broadleaf weeds have leaves similar to most plants, growing from a recognizable stem. Most likely, you'll have no problem identifying grass. Depending on how well you inspect your lawn, however, weeds may become well established before you even realize a problem exists.
Whether you have a lawn of St. Augustine (Stenotaphrum secundatum) or Bermuda (Cynodon spp.), two of the most common types of grasses in South Florida, crabgrass (Digitaria ischaemum) and quackgrass (Elytrigia repens) can make your lawn look like a tangled mix of grass. Controlling crabgrass in the north, where it dies out every year, is easier. The occasional frost may kill it in South Florida, but more aggressive tactics such as shading the area, using a herbicide or even baking soda, followed by re-sodding, is often the only way to get rid of it. Quackgrass is a perennial, meaning it will come back every year whether it has seeded properly the year before or not. Control methods are the same for crabgrass in South Florida.
A number of species commonly known as pennywort or dollarweed are found in South Florida, with the most prevalent being largeleaf pennywort (Hydrocotyle bonariensis). They thrive in warm, moist conditions. Also, better drainage prevents recurrences of the weed. Spotted spurge (Euphorbia maculate) also is problematic because it produces a milky substance that causes skin irritation. It has small green leaves with a deep purple spot in the center. Both weeds are killed with a broadleaf herbicide.
The prevention of warm-season weeds is difficult, especially in an area that does not get cold enough to kill them in the winter. After determining what specific weed is the problem, do research. Crabgrass, for example, cannot take shade well. Keeping your lawn at a proper height helps choke out some of these weeds. Also make sure your lawn is watered and fertilized properly to ensure a healthy lawn.