Weeds make flowers and flowers make seeds—lots of seeds. Although plants don’t have legs or feet to move around, they do have the ability to move their seeds. In fact, there are several seed dispersal mechanisms used by plants to move about. This is the reason why weeds are seemingly a never-ending problem for farms, lawns, and gardens. Eventually, weeds will always find their way back to you.
Some plants produce seeds that are dispersed by wind. There are several classic examples of weeds such as dandelions, thistles, burnweed, and trampweed which have feathery seeds that float in the air and are easily carried by the wind, sometimes traveling for miles. Pine trees and maples have winged seeds that spin like tiny helicopters. Have you ever noticed that thistle weeds seem to congregate along railroad tracks? The reason why is because the seeds of thistles will blow down the tracks as trains pass and often hitch a ride on the train itself.
Another common type of seed dispersal is from animals eating the seeds and fruits of various plants. Poison ivy, Chinese privet, beautyberry, honeysuckle, and eastern redcedars have berries that are attractive to birds, which digest the seeds and then plant them wherever their droppings fall. Birds like to spend time sitting on fence lines and power lines, which is where we frequently see these types of weeds growing.
Many plants have sticky seeds that attach to the fur of animals and hitch a ride. Examples of these include field sandspur, foxtails, creeping beggarweed, hairy beggar-ticks (also known as Spanish needles or devil’s pitchfork), lawn burweed, cocklebur, and catchweed bedstraw. Many grass species also have the ability to stick to fur or clothing. You will often find these types of weeds and grasses along footpaths or animal trails.
Black walnuts and sycamores are examples of native trees that are often found near rivers and streams because their seeds will float. There are many examples of aquatic weeds that are found near swamps, ponds, and creeks. There are also many weeds that thrive in low lying fields and ditches that frequently stay wet. Many of these plants have seeds that can float and survive in water for extended periods. Curly dock is a weed commonly found in ditches that produces tiny fruits with wings that are dispersed by both water and wind. In fact, many wind-dispersed seeds are also good at floating.
Probably the most interesting form of seed dispersal involves ballistic seed capsules. Explosive dehiscent seeds have a spring-like mechanism for shooting seeds when touched or dried out.
Some examples of weeds with explosive seeds include woodsorrel (Oxalis), hairy bittercress, jewelweed (touch-me-not), and wild violets. These types of exploding seeds don’t go as far as other seed dispersal mechanisms; however, it may be that these plants are trying to avoid being eating by animals, which involves moving quickly rather than long distances.
If you are constantly fighting any of these highly mobile weeds in your pasture, lawn, or garden, keep in mind that half the battle is controlling them before they go to flower and produce more seeds. Another important consideration is keeping weeds in check along fence lines, power line rights-of-way, railroad tracks, and roadside ditches—so weeds don’t come back as quickly.
Paul Pugliese is the Extension Coordinator and Agricultural & Natural Resources Agent for Bartow County Cooperative Extension, a partnership of The University of Georgia, The U.S. Department of Agriculture, and Bartow County. For more information and free farm, lawn, or garden publications, call (770) 387-5142 or visit our local website at extension.uga.edu/bartow.
