Why do weeds grow? They often colonize empty or bare soils with recent disturbances, as some need constantly shifting environments to survive. Most are primary plants, meaning they fill soils before other, larger, and woody specimens. Their seeds, rhizomes, or rooting stems find empty soils and fill them with foliage.
As we cultivate our gardens, we create spaces for weeds to germinate. Any disturbance invites them, whether it be transplanting seedlings or applying compost. The best way to combat their spread is to catch them while young. Immature weeds often have weak root systems, and they pull away easily from the soil.
I like to look at weeds as blessings in disguise. They grow fresh green leaves that turn into compost or mulch. Take your weeds and recycle them for a consistent flow of nutrients that you can apply freely to garden soils. Weeds are plants, and they contain nutrients that feed other plants when they decay.
Let’s learn how to identify common weeds and find how they spread to prevent them from roaming further. Here are 11 aggressive fall weeds to watch for—they’ll take over your garden if you leave them to grow!
Lemon balm is a common garden herb, but it’s also a rampant spreader. Individual clumps reach two to three feet wide when mature and grow hundreds of seeds. They germinate readily in gardens, forests, and parks. Some states in the Pacific Northwest label lemon balm an aggressive weed because of its self-spreading nature, particularly in the fall.
Keep lemon balm in a container to limit root growth, and cut spent flowers before they produce seedheads. These two actions limit lemon balm’s weedy nature, allowing you to enjoy its aromatic leaves without dealing with its aggressive nature.
Lemon balm seedlings come out of the soil easily. Pull them when they’re young, and they won’t grow into hardy adults. Once they establish themselves, lemon balm specimens are difficult to eradicate. Pull them repeatedly until they stop sprouting new stems.
Like lemon balm, mint is a self-spreading herb that escapes from backyards. It uses seeds, rhizomes, and rooting stems to creep into other perennials and snuff them out. If you grow mint in your yard, you’re well aware of its weedy nature!
Use similar techniques for limiting lemon balm for mint. Grow it in raised beds or containers, and cut spent flowers before they mature into seedheads. Any stem that touches the soil may root, so ensure they stay away from your precious garden soil.
Mint seedlings are short and aromatic, resembling larger plants with smaller leaves. Pull them while they’re young and transplant them into new containers, or throw them in the compost if you already have enough mint.
European self-heal can be an aggressively spreading fall weed due to its rooting stems and underground rhizomes. You’ll find it in lawns, garden beds, and cultivated fields. It thrives with disturbance, rooting freely from broken stems.
European self-heal is a close relative of the American native species lance leaf self-heal. Remove European plants, then place native ones in their place. They appreciate similar conditions and will cover bare soil, so the weedy versions can’t get a good footing.
Remove self-heal effectively by pulling young seedlings. When immature, their root ball is small and weak, and the perennials will come right out of the soil. Keep pulling until no seedlings remain–annual attention ensures they stay away.
Hairy cat’s ears resemble dandelions, with clusters of yellow aster flowers atop slender stems. They grow rosettes of hairy, green leaves that lack white liquid sap. They aren’t common in wild landscapes but are in cultivated gardens and disturbed land. When left to flower, the blossoms morph into dandelion-like seed heads that blow in the wind.
Hairy cat’s ears typically spread from lawns into gardens. Their seeds waft onto fresh soil, germinate, and form a thick taproot. Pull up plants in fall or spring to limit their spread. You may also leave them in the ground and mow or prune the flowers before they form seed heads. They’ll continue growing but won’t sprout in new sites.
Hairy cat’s ears grow edible leaves, flowers, and taproots. Harvest and cook the plants, as they are tough and bitter fresh. These weeds are poisonous to horses, so remove them in areas where horses roam freely.
Creeping wood sorrel is a common garden weed with a worldwide distribution. It sprouts red-green shamrock leaves and yellow flowers. With successful pollination, the blossoms mature into pods that spread viable seeds. Creeping wood sorrel also sneaks underground, using rooting rhizomes to pop up in new locations.
This weed often arrives from potting soil or compost in other gardens or potted plants. Inspect incoming soil for the perennial, and pull it when you see it. If creeping wood sorrel establishes itself, dig up the entire plant. Root fragments sprout new plants—if they grow leaves, pull them up. They’ll disappear as you remove their roots and seeds annually.
Watch for this aggressive weed’s growth in fall and spring. The plants speed up their growth during these mild seasons, as ample sunshine and water encourage their survival. Pull them while they’re small to avoid their hostile takeover.
Spotted spurge is the bane of many a gardener! It invades cultivated spaces, but it also survives in sidewalk cracks, roadsides, and clay soil. Spotted spurge sprouts with warm summer temperatures, sows seeds, and dies. It’s an annual weed that plagues bare soils during the growing season.
This weed leaks a milky, skin-irritating sap when its stems break. Wear protective gloves to keep your skin safe while pulling. Remove this weed with a hoe or your fingers, loosening the roots from the soil. If root fragments stay behind, try to dig them out. They’ll sprout new plants. You can also leave them and pull new stems as they grow.
Spotted spurge disappears from backyard spaces with repeated removals. It needs to sow seeds to sprout the next year, and fall is a prime time for seed formation. If you remove plants early in summer, you prevent them from self-seeding during autumn.
Purslane, like spotted spurge, sprouts annually from seeds in the summer months. Roots grow from thick, fleshy stems, meaning broken stems can form new plants! Look for green succulent leaves, purple stems, and small, yellow flowers. The flowers form fruit capsules that drop seeds when they’re ripe.
Purslane dominates as a summer weed and sows seeds during late summer and fall. Pull plants before the flowers form fruits, and remove any broken stems from the soil. Purslane is less invasive than spotted spurge, but still hardy enough to survive on sidewalks, driveways, and abandoned lots.
This weedy succulent is edible! Prepare the leaves like nopales cactus, cutting them up and sautéing them in oil with salt and pepper. Add some leaves to smoothies for a smooth, mucousy texture with beneficial vitamins and minerals.
Hairy bittercress also goes by the name popweed because it pops seeds everywhere! This aggressive weed has hairy green leaves sprout in a rosette, and small white flowers in late summer or early fall. They emerge from the center on short stems. They form slender pods that explode with ripe seeds on contact.
Hairy bittercress is edible, fresh or cooked. It tastes like a mixture of broccoli and bok choy. Use it in salads, smoothies, or sauteed greens recipes. Seeds sprout readily during the fall, so you’ll have ample weedy greens during cool, mild months.
Hairy bittercress thrives in cool, wet weather. It’s a common weed throughout hardiness zones four to eight in spring and fall. Seeds stay dormant in soils until they sense optimal conditions. Pluck them before they sprout seeds to avoid future infestations.
Chickweed is another edible weed that takes over gardens. It sprouts small, fleshy green leaves and white flowers in star shapes. They morph into seeds that sprout during fall or spring. Although this weed is more aggressive in spring than fall, it may still spread while it’s cool, wet, and sunny.
Remove chickweed seedlings from your garden by pulling them at their base. They grow shallow roots that easily come out of tender soils. Chickweed sprouts from stem fragments with roots, so be sure to remove any scraps from the site. Compost chickweed, or prepare it to eat.
Use chickweed in smoothies, salads, and casseroles. The tender leaves are palatable fresh or cooked, and are abundant in hardiness zones four through eleven. Find chickweed around rivers, meadows, and moist gardens.
Purple dead nettle doesn’t sting like other nettles, but it does quickly spread in garden settings. Look for mint-like plants that emerge in the fall with green, fuzzy leaves. They grow taller throughout winter and spring, with red leaves at their stem tips. Purple flowers bloom in spring and fall, followed by seeds that ripen.
Reduce purple dead nettle by cutting its life cycle short during autumn. Yank up any seedlings as you see them. This weed sprouts shallow roots, making removing it with your bare hands a simple task. Throw the pulled plants back on top of the soil as mulch, or put them in your compost for free nutrients.
Purple dead nettle appreciates cool, wet conditions during its lifetime. It often hitchikes in with container plants. Inspect any new plants you bring into your garden during autumn for young purple dead nettles because a single specimen can create dozens more.
Annual bluegrass is a non-native weedy grass from parts of Africa, Europe, and Asia. It thrives in cool fall weather, germinating readily and growing rapidly. Seedlings quickly mature into adults, who then sow hundreds of viable seeds. The seeds stay in the soil for years, meaning a single plant can multiply exponentially for years to come.
Although this annual is extremely aggressive, it also sprouts weak shallow roots. Pull plants easily in the fall when soils are moist. With repeated pullings every fall and spring, annual bluegrass populations will decline and disappear. Watch for small, needlelike grass leaves poking up out of bare soil. Seeds sprout in borders, raised beds, and near other perennials’ stems.
Annual bluegrass seeds are hardy, so you’ll want to keep mature specimens with viable seeds out of your compost. Dispose of them away from your garden, or bury them at least six inches below the soil to decompose.
