Identifying Annual And Perennial Weeds: The Biggest Differences And Why It Matters

Getting rid of weeds in your garden and yard is an important task in any homeowner's quest to maintain a healthy landscape. These often hardy plants often pop up in unwanted places, competing with desirable plants for space, nutrients, water, and light. To deal with these invaders effectively, you have to understand their life cycles and how they reproduce. That knowledge starts with identifying whether the plants are annual or perennial weeds. In a nutshell, annuals live out their entire life cycles in a single year and spread by seeds, while perennials come back year after year. You may also run into biennials, which go from seed to flowering to seed production over two years.

Not only are weeds categorized in a similar manner to the welcome plants in your outdoor space, but there are subcategories within those delineations as well. For instance, some annuals grow in different seasons and certain perennials spread via seed while others do so underground. Zeroing in on the weeds you're dealing with will help you develop an effective strategy for eliminating them from your lawn and garden. There are several ways to identify what type of weed you're dealing with, including watching how they grow, looking at their roots, and observing their seed production.

Of the different weed types, annuals are largely the easiest to identify and control. While summer annuals grow in the spring as soon as the weather starts to warm, and winter annuals pop up at the end of summer, you can identify both types with the same approach. In contrast with perennials, these weeds have a short window of time to germinate, grow, flower, and go to seed before they die. Given that they go through these phases quickly, observing swift lifecycle changes can indicate you're dealing with an annual weed. 

Unlike perennials, annual weeds also tend to have shallow roots, so it's easy to spot them when you pull them out of the ground. In fact, hand pulling is one effective way to rid your lawn or garden of these plants. You want to catch these annuals as soon as possible and definitely before they go to seed, as that's how they all spread. Annual weeds also tend to like parts of your landscape where the soil is disturbed and otherwise unestablished, such as new lawns or gardens, making their location a possible identifying factor. Annual weeds include crabgrass, purslane, chickweed, prostrate knotweed, henbit, hairy bittercress, and creeping wood sorrel, among others.

Two different kinds of perennial weeds may invade your outdoor space — simple and spreading. Both live significantly longer than annuals, with multi-year cycles that span more than three years. Simple perennials grow independently, so if you dig one up, you'll see a single root system. You need to remove these roots completely from the soil when weeding so the plants don't keep returning for several years in a row. Even so, simple perennial weeds are easier to banish from the yard than their spreading cousins because they spread by seed. Some examples of simple perennials you may know well are dandelions and plantains.

Spreading perennial weeds, like white clover, yellow nutsedge, and ground ivy, don't proliferate by solely by seeding like the other weed types on this list. Instead, these persistent plants send out runners either over the ground or underneath the soil to spread. Look at the unwelcome plants in your garden or yard. If they are connected to one another by stems running above the ground, called stolons, you're likely dealing with a spreading perennial weed. 

Other times, the connection isn't obvious until you attempt to pull up the weeds and notice they are tethered together by rhizomes under the ground. These stolons and rhizomes reach out to a neighboring portion of your outdoor space and develop new plants that grow and spread in the same way. Spreading perennial weeds are the hardest to control.

Annuals and perennials aren't the only weed types that can become a nuisance in your yard. Biennials like bull thistle, common burdock, and wild carrot have a two-year life cycle and are also a threat. You can identify these weeds by their above-ground appearance and roots. During the first year of a biennial weed's life, it will germinate and grow but won't flower. Instead, you'll see a cluster of leaves close to the ground, referred to as basal rosettes. Seeing these rosettes pop up in your yard is a good indication that biennials are calling your property home. 

Likewise, while biennial weeds reproduce through seed like annuals, their roots systems are different. Instead of shallow ones like annuals, biennial weeds usually have taproots, much like simple perennials do. Along with the rosettes, these deep roots are a biennial's telltale signs. You must remove these roots completely or kill them when pulling the weeds to prevent the continuation of the plant's life cycle. 

In their second year of life, these unwanted plants bolt, flower, and go to seed. When ridding your lawn of these weeds, you want to catch them in the first year when they form their rosette foliage or during the second year before they seed and spread. If you wait until year two, the flower stalk that develops can make hand-pulling and removing the taproot a bit easier.

Properly identifying the weed you're dealing with gives you the best chance at eliminating the invader from your lawn. For instance, you want to remove annuals as soon as you notice them, since they will quickly go to seed and spread, creating a bigger problem. You can keep annual weeds under control by pulling them out of the ground by hand, treating them with herbicides, or covering and smothering them with mulch. Their shallow root systems make them easy to remove. 

Perennials mistaken for other types of weeds will persist in your yard, especially if you treat them as individual plants. The spreading variety of these weeds is either connected above or below the ground, and removing this type effectively requires you to understand its growth habit. You can do this by hand, but beware that completing this task is labor intensive. Be sure to dig around the plant, follow the rhizomes or stolons, and remove all parts of the plant.

Determining which invaders are biennial is also crucial. If you mistake one for an annual, you might not think to remove the taproot, allowing the weed to return. While you essentially have two years to deal with these types of weeds, removing them and their deep roots as soon as you see them will give you the best chance for success. If you miss the basal rosettes and only see them when they bolt, be sure to remove the plant and root before they seed in the second year.

While there are viable strategies for ridding your lawn and garden of weeds once they emerge, the best course of action is prevention. That's because keeping on top of unwelcome visitors in your outdoor space can be a daunting task once they start to grow, depending on the size of your yard or the scale of your problem. Applying a pre-emergent herbicide to your lawn in the spring can stop summer annual weeds from germinating. Meanwhile, doing so in the fall can protect your yard from winter annuals. But nothing is foolproof, and some annual weeds may still break through. To deal with these, treat them with a post-emergent herbicide, pull them hand, mow regularly, seed any bald patches, and mulch where needed. Biennials can also be prevented through mulching or, for breakthroughs, with post-emergent herbicides.

You can prevent the most challenging weeds — perennials — with pre-emergent herbicides and mowing regularly to maintain a robust carpet of grass. Landscaping fabrics and filling in any bare spots in your lawn can also keep perennial weeds at bay. For prevention in gardens, mulching is an effective prevention method. Be sure to choose the best type of mulch; ideally, one that will prevent weeds while adding nutrients to the soil. Growing ground cover plants in your lawn and garden can also help block weed growth.

For weeds that break through in the lawn, try herbicides containing glyphosate. That said, there are safer store-bought weed-killer alternatives you could use instead, as glyphosate might harm your soil. Some of those options include vinegar, glufosinate, and pelargonic acid.