How Do Weeds Spread?

Dandelion Ready to Spread

When spring rolls around, weeds in the lawn, garden, and landscaping become prevalent in many yards. “How do weeds spread?” is a common question asked by many homeowners as they look for ways to solve this pesky problem. 

In order to combat weeds, the source of the weeds needs to be revealed to help eliminate them in the future. This article will discuss the various ways that weeds spread to help reduce the number of weeds you have to battle each year.  

Lawn Mowers 

Many people likely do not suspect the lawn mower to be a weed spreading culprit. However, it is the one machine that routinely comes in direct contact with weeds. When the lawn mower is set to mulch or side discharge, the weeds that hold seeds are chopped up by the mower blade and redistributed back into the lawn. The seeds that make it to the soil have an opportunity to produce more weeds. 

Additionally, the weed seeds have the ability to stick to the mower and eventually indiscriminately fall back into the yard . For example, if a weed filled backyard is mulched first, it has the ability to contaminant the weed-free front yard from the weed seed transfer on the mower. 

Commercial lawn mowers are not immune to spreading weed seeds. The typical lawn mowing service cuts several lawns per day. The odds are that a portion of these lawns are not remotely close to being free of weeds. Of course, the lawn service is likely not going to thoroughly clean the mower after each lawn they mow with weeds. Therefore, the weed seed has the ability to transfer from one lawn to the next through the commercial mower. 

If you are serious about preventing weeds, we recommend mowing your own lawn. Use the bag option on your mower to collect the weeds when they are most prevalent (i.e. the spring), instead of mulching or side discarding them back into the lawn. 

Other Equipment

The lawn mower is not the only machine that is guilty of spreading weed seed. There are numerous pieces of equipment and tools that can contribute to the spread of weed. Essentially, anything that comes in contact with the weeds has the ability to spread them. 

Grass Seed

If you look at a bag of grass seed at a store such as a home improvement center, you will likely notice it provides an overview of the seed contents. Surprisingly, it is not all grass seed in these bags. A certain portion of the seed, particularly in cheap seed, will contain fillers and weed seed.

As we have stressed in previous articles, it is important to purchase high-quality seed that is very close to being 99.99% weed free. Also, look for a high germination rate of at least 85% for the grass seed. Pennington provides an excellent guide on how to read a grass seed label if you are confused on what to look for in a quality seed. 

The Wind

While it is often fun for kids to blow the white headed dandelions all over the yard, this is effectively spreading seed. This process occurs naturally with the wind with many types of weeds. It is very difficult to prevent weeds that transfer into a yard from the wind. Barriers such as fences or tall landscaping can help, but weed seed often makes it beyond these barriers. 


The rain, sprinklers, rivers, or other water producing objects have the ability to spread weed seed. For example, a heavy rain may pool on your neighbors grass and then eventually drain onto your lawn while carrying the weed seed. Some weed seeds and roots float, such as the pepperweed, which grows near water, explains the University of South Dakota

Humans and Pets

A friendly game of football in the backyard, for example, can do an excellent job at transferring weed seed via shoes, clothing, hair, or other areas of the body.

Animals are another culprit in the spread of weeds. Seeds can latch onto fur and later drop off in another location. Additionally, an animal can eat weeds and pass them through its digestive system to later produce waste which contains seeds. 

Controlling Weeds

Here are some tips to control lawn, garden, and landscape weeds:

  • Mulch – mulch provides a blanket of material such as wood or pine straw that smoothers the weeds. It should be about 2 to 3 inches deep to eliminate the sunlight that allows weeds to flourish in the soil. Do not exceed 4 inches of mulch since this can deprive the landscape plants and trees of water and other nutrients. 
  •  Mow High – Weeds love the sunlight. If you mow at a taller height, you will help shade out weeds and assist in keeping the soil moist. 
  • Thicken Lawn – A thicker lawn will crowd out weeds. A lawn renovation should be considered if your grass is thin and/or has a decent amount of weeds. Bare spots should be patched with a quality grass seed. Additionally, thin lawns often benefit from overseeding in the fall or spring. A fertilizer program should be followed to keep the lawn growing healthy.
  • Identify & Take Action – Determine the type of weeds growing in your yard and use an appropriate weed control product. For example, dandelions and clover can be eliminated with a broadleaf weed spray or a weed and feed product. Crabgrass can be controlled by using a pre-emergent in the spring. Preen has a state-by-state weed identification database which is useful  to determine the types of weeds you may have growing in your yard. Once you identify the weeds, you can find products that control these weeds. 
  • Manually Pull Weeds – There is nothing wrong with pulling weeds by hand or using a weed removal tool. This is not just reserved for the garden or landscaping beds. It can also be done in the lawn if the weeds are minimal. Pull the weeds before they begin to seed to avoid them spreading.