Are weeds bad for your soil, or are they just a cosmetic issue?

I remember as a child being confused why adults would dig up dandelions and consider them to be a nuisance. "They're not weeds, they're flowers!" In fact, there are some plants that are considered weeds simply due to personal preference and their ability to sap nutrients away from the plants you're intending to grown. However, some plants can be truly detrimental to other plants in your yard and to the environment--some of them are weeds, and some of them are planted intentionally, but can still spread out of control!

What makes a weed a weed?

In general, a weed simply means a plant growing where it's not wanted. This means that the same plant might or might not be a weed depending on where it's growing: the same grass can be a weed in your flower bed that you're intentionally growing in your lawn. 

Can't we all just get along?

A monoculture, which refers to growing a single variety of plants in an area by itself, is actually quite difficult to maintain since plants naturally spread themselves by seeds or runners and intermingle with each other (think of the diversity a native forest or prairie environment). All gardeners know the uphill battle of pulling weeds that are constantly infringing on their vegetable patches or flower beds, and many homeowners invest in pre- and post-emergent herbicides to keep their lawns looking well-kept. So is all the effort of weed removal and prevention worth it?

The issue with weeds is that unwanted sturdy plants can allocate nutrients, water, sunlight, and other resources for themselves at the expense of whatever you are trying to grow, especially if your desired plants are more slow-growing than the weeds. And some weeds release chemical compounds from their roots that inhibit the growth of other plants, an ability known as allelopathy (for example chickweed and creeping thistle). In the case of a lawn or ornamental garden where your main intention is a specific aesthetic goal, you may have no other option but to keep battling it out against the weeds to achieve your desired results.

However, in gardens with more flexibility in choosing plant varieties and placement, you have more strategies to transform plant diversity into an asset rather than a nuisance. Instead of monocultures, some farms and gardens utilize strategies such as companion planting (growing multiple plant varieties in the same area) and cover cropping (growing a plant to cover the soil rather than for harvesting) to cover bare soil and beat the weeds at their own game. Taking a cue from diverse natural ecosystems, traditional agriculture intermingles complementary crops with each other, such as the classic Three Sisters combination of corn, squash, and beans. When grown together, the corn stalks provide a trellis for the beans, the beans add nitrogen to the soil though specialized bacteria in their roots, and the squash grow large leaves that block out sunlight and suppress weeds. Over the winter, cover crops like clover, mustards, or even oats can guard your soil from being overtaken with weeds between regular growing seasons. (Did you know clover adds nitrogen to your soil?) Instead of isolated plants growing in bare soil, a garden can be a community of plant varieties working together to fill in the gaps and block out harmful weeds.

Invasive species

While some plants are weeds because people have arbitrarily labeled them "out of place," invasive species are plants that truly do not belong and will grow out of control to the point of harming the ecosystem. Invasive species are typically introduced by humans from a faraway place to a new environment were they have no natural predators keeping them in check. Common examples in North America include kudzu vines, bamboo, and English ivy. These plants might seem like obvious examples of weeds when they reproduce rapidly and spread dramatically, but some invasives go under the radar when people plant them intentionally in their yards. These include plants like the Bradford pear, the butterfly bush, and Japanese honeysuckles. Plants in this category might have pretty flowers and might not seem like weeds, but they require very close attention because of their high risk of spreading, becoming a nuisance, and threatening the survival of other plant species. Click here to learn more about some native alternatives to invasive plants (and remember that whether or not a plant is invasive depends on your specific location). 

To sum up, if you find unwanted plants in your yard, or wanted plants growing in unexpected places, you might want to do some research. Is it a plant that causes harm to your other plants or to the broader ecosystem? Some plants are labeled weeds although they can be beneficial (or even edible in the case of dandelions!), and other plants aren't perceived as weeds although they can be harmful to the ecosystem (like Bradford pear). It's hard work digging up weeds in your yard -- it's worth considering the species you choose to plant and making sure they work well together to not make more work for yourself!

Learn more about weeds with a fact sheet from the Weed Science Society of America: click here.