5 Herbs You Can Grow To Help Block Out Weeds In Your Garden (& 7 To Avoid)

Weeds are a pretty pernicious problem for most gardeners, and unless you’re comfortable using herbicides, the growing season probably finds you kneeling in your borders pulling out purslane, portulaca, dandelions, poison ivy, and other pesky intruders. Fortunately, there are some natural weed control methods to try, and growing plants that can shoulder out weeds is one. Herbs can be particularly handy for the task, and some even produce allelopathic chemicals that may support this process. 

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Instead of rehashing the usual recommendations, we dove deep into the research archives of academic and government institutions looking for natural ways to combat weeds in your garden. During our research, we discovered something really cool: There are a few herbs that have some incredible compounds in their makeup, which scientists have used to send weeds running for the hills. However, it’s important to note that these plants weren’t studied growing in the ground, instead, their organic compounds were extracted and tested on weed seedlings. That means planting one of these herbs isn’t going to garner the same level of weed annihilation. After all, there’s no plant that acts as a true herbicide, so you’ll likely still find some stubborn weeds pushing through. But they can help lower the amount you’ll see, so they’re worth experimenting with.

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Here are five herbs whose organic compounds have shown promise in combating weeds, plus tips for how to keep them thriving in your garden. We’ve also included seven herbs that are sometimes recommended for suppressing weeds, but which you might want to think twice about adding to your garden. So break out the beakers and lab coats and buckle up for a science-backed guide on growing herbs to block out weeds in the garden.

Behold the zesty power of ginger (Zingiber). Used worldwide for centuries for medicinal, culinary, and cosmetic purposes, scientists are now testing to see how weeds fare against its oil. It turns out that some compounds in ginger are pretty good herbicides. A 2019 study published in (where else) “Plants” found that ginger essential oil had “significant” abilities to prevent seed germination and root development for three pesky weeds: Common purslane (Portulaca oleracea), ryegrass (Lolium multiflorum), and pampas grass (Cortaderia selloana). 

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Ginger is slow-growing. However, once established, it produces a nice mat of knobbly rhizomes, which can also prevent weeds from germinating around its vicinity. This action of the rhizomes is one reason why wild ginger can be such a pest in some countries. 

Given that established ginger has a chance at helping to keep weed growth down, let’s talk about how to avoid the common mistakes everyone makes growing ginger so that yours thrives. Ginger needs humidity, moist soil, and around five hours of light daily. To prevent weeds germinating around freshly planted rhizomes, apply mulch. Expect to dig up the rhizomes in the winter if you’re in a colder climate. Don’t have the right conditions to grow ginger? You can also try using ginger as an ingredient when watering garden plants.

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Turmeric is part of the ginger family and was also found to be a powerful herbicide in the study mentioned above. Researchers noted, in particular, that turmeric’s essential oil contained properties that made it effective as a post-emergent bioherbicide, while ginger’s was more potent during the pre-emergence or seed germination phase. So, in theory, planting both turmeric and ginger in your garden could create a one-two-punch combination that tackles weeds at multiple stages of their lifecycle. In addition, once grown tall, turmeric plants can help suppress weed growth another way. The leaves will prevent light from reaching the ground, killing the weed seeds, and the rhizome system could further help muscle out unwanted plants.

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Turmeric is great for lazy gardeners because it has a very low chance of getting out of control. While it has thick rhizomes that could outcompete plants with more delicate root systems, its flowers are sterile, so it can’t self-seed or spread aggressively. Like ginger, turmeric needs heat and humidity to thrive. It also prefers its soil to be slightly acidic and consistently moist. To give you an idea of its ideal growing conditions, farmers in India report that turmeric grows best during their monsoon season. Mulching the young rhizomes can help stop weed competition at this stage and give them the warm, moist conditions turmeric loves. It does okay-ish in containers but will need a lot of water, so consider using self-watering pots to keep it happy. Side note: If you don’t want to shell out upwards of $100 on one, you can also DIY a self-watering planter for cheap. 

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In extracted forms, rosemary is a weed-controlling powerhouse. It’s full of allelochemicals, which are basically compounds that prevent competing plants from outgrowing it and taking all of the nutrients before our main character plant can get its share. Allelopathy is a fascinating world, and researchers are looking for ways to harness it in herbicides. A 2022 study in “Plants” found rosemary essential oil became the garden version of Thanos, destroying germination and seedling growth in Indian goosegrass (Eleusine indica), Bermuda grass (Cynodon dactylon), hairy crabgrass (Digitaria sanguinalis), redroot pigweed (Amaranthus retroflexus); do you want us to go on? Because we can. Suffice it to say, rosemary essential oil seems to significantly help stamp out germination in many weed seeds.

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However, results from growing a rosemary bush compared to applying isolated compounds to the soil are far less certain. But luckily, besides its potential allelopathic properties, rosemary also forms dense, bushy growth, and a robust but fine network of roots, both of which are perfect for outcompeting weeds.

Caring for a rosemary herb plant is relatively easy, and once established, the bushes will give you a steady supply of rosemary sprigs. Rosemary is drought-tolerant but likes well-draining soil that’s not heavy with clay. Plants prefer full sun but will live in partial shade if that’s what you’ve got. Rosemary does not like overwatering or excessive humidity, and consistently wet or moist environments can make it susceptible to powdery mildew and root rot. These tough shrubs are not only great in herb gardens, but pollinators love rosemary, and they’re also one of the plants to grow if you want to have goldfinches flocking to your yard. 

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Marjoram (Origanum majorana) isn’t as popular as some of the other herbs on this list, but its potential for being a powerful weed inhibitor should make you take note. A 2021 study published in “Molecules” explored the possibilities of using marjoram as an herbicide, isolating its various compounds to determine what, if any, viable options there might be. The study found marjoram had 25 compounds, including some that had never been identified before, and at least three of these were strong candidates for being turned into natural weed killers. These compounds were put up against a commercially available herbicide, Logran, and found to be as, if not more, potent.

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Of course, simply growing a marjoram plant in a bed is not going to annihilate all weeds in your yard. But you might find that this spreading perennial has somewhat fewer weeds popping up beneath its creeping stems. Whether that’s because it’s a groundcover (which are great for smothering weed seedlings) or because of the compounds within the plant, we’re not sure. But either way, this aromatic herb is worthy of a place in your garden. Marjoram likes being planted in areas that have full sun and neutral or slightly alkaline soil. It’s hardy once established, handling drought and heat like a champ, but you may want to bring it inside if you live somewhere that gets really cold during the winter. Harvest the leaves before the flowers bloom to get the best flavor, which is described as sweet and spicy but still a little milder than oregano. 

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Lavender’s essential oil has been tested for years for its herbicidal efficacy since it’s chock full of allelopathic compounds like linalool, 1,8-cineole, and camphor. A 2022 study in “Plants” found its extracts and essential oils were particularly potent against nettle-leaf goosefoot (Chenopodium murale) and redroot pigweed (Amaranthus retroflexus), while a 2019 study in “Molecules” found the Angustifolia cultivar (commonly known as English lavender) reduced germination of ryegrass (Lolium multiflorum) by 87.8%. While a lavender bush is unlikely to “kill” weeds in the way an essential oil can, established plants can hold their own against less aggressive weeds. Their growth habits alone make lavender bushes one of the best plants to try for naturally keeping weeds out the garden. They grow thick and dense, blocking most weeds from popping up in their vicinity.

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Growing lavender takes some strategy as it can be a bit of a prima donna. It absolutely hates sitting in moisture and will rot quickly in clay-heavy soil. Lavender loves full sun and only wants a drink of water here and there. Overwatering is one of the easy mistakes to avoid when growing lavender for the first time. Do not mulch around lavender, as this can retain moisture near the base, which may, again, lead to rot. A happy, mature lavender plant will get about 3 feet wide so make sure you’ve got enough space around it for the bush to grow into its final form. The leaves, flowers, and seeds can all be used, so cut back whatever you need once the flowers fade and feel free to go crazy; a mature lavender plant can handle it. 

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During our research, we initially hoped that garlic might be a powerful ally for allelopathically warding off barnyard grass. A 2023 study published in “PLOS One” found garlic’s essential oil was the most successful out of 12 tested, stopping barnyard grass from developing roots and depleting its chlorophyll supplies. This is quite impressive, given that barnyard grass (Echinochloa crus-galli) is no joke of a weed. However, we had to boot this allium onto the “don’t plant to stop weeds” list, because the results don’t translate to garlic growing in the ground. Barnyard grass is an ongoing problem in garlic fields, along with many other weeds. Thanks to its thin, shoot-like leaves and slow growth, garlic can quickly get outcompeted by germinating weeds. And as any experienced vegetable gardener knows, weeding garlic can be an ongoing, painstaking task. 

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While we wouldn’t tell anybody to plant garlic for weed suppression, this doesn’t mean you shouldn’t grow it. Garlic is a great addition to any vegetable patch, and there are even unexpected benefits of planting garlic by your roses. Garlic needs loose soil that’s well-draining so its cloves can grow easily. Plant your garlic somewhere that gets full sun and watch for bulb rot, especially when you’re getting close to harvesting. Mulching and removing weeds by hand is important to make sure the garlic plants don’t get choked out. Cut off the flower and stem; this will ensure energy stores go to growing the bulb, instead of seed production. 

Comfrey (Symphytum officinale) has an interesting history. Its scientific name roughly translates to “a plant that heals injuries,” thanks to its tradition as a medicinal herb despite it being somewhat toxic. Still, the reason (well, besides the whole “might poison you” part) you might want to skip adding it to your garden is because comfrey, like life in “Jurassic Park,” finds a way. It will easily regenerate from the tiniest of pieces left over in the soil, making it nearly impossible to eradicate. Plus, it grows aggressively and can spread over neighboring plants, suffocating them and shutting out the light they need to photosynthesize. 

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This enthusiastic growth on the part of comfrey does mean it can block out weeds, and the leaves can be used as a nutritious mulch or fertilizer. If you live somewhere like Northern Montana or North Dakota (areas outside its hardiness zone) and have an unused area in the garden that merely acts as a breeding ground for weeds, filling it up with comfrey could be an option. But be aware that if you ever want to remove the patch, you could still have a serious undertaking on your hands. And do not plant comfrey under any circumstances if you’re located in a state where it is categorized as invasive, such as the eastern U.S. 

Catnip (Nepeta cataria) is tough to add to this list because it has a lot of beneficial properties. It’s one of the best plants to use as a form of natural pest control in your garden, it’s great for attracting pollinators, and let’s face it, your cats are big fans. Those are pros; now let’s talk about the cons.

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 Catnip grows so fast and is so prolific a spreader that it’s considered a weed by some agricultural departments. Also, while your cat may like the smell, some people aren’t as enamored. Its aroma has been called a cross between thyme and oregano, which doesn’t sound so bad, but others refer to it less delicately as a bit “skunky.” 

Chives (Allium schoenoprasum) are surprisingly fast-growing herbs to cultivate in the garden, which is why we caution against planting them. On one hand, they’re super hardy and don’t really have many fungal or pest problems. Their flowers are so pretty that they’d do well as ornamental additions to your garden even if you never cook with them a day in your life (but they do complement many recipes). They can also grow thickly, squeezing out weeds in the process. 

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However, chives are crazy good at self-seeding and will spread quickly without you noticing. If you’re able to stay vigilant and remove spent blooms, you may be able to keep them under control, but we’re not making any promises. 

Man, we wish we didn’t have to put mint on the “No” list because it has significant allelopathic properties, but it can quickly become a problem plant. The 2019 study in “Plants” that focused on garlic and turmeric essential oils gave a look at peppermint (Mentha piperita L.) essential oil, too, and found that it could completely prevent seed germination of ryegrass while significantly hampering germination for barnyard grass and common purslane. 

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However, most mints are just way too aggressive to control because they use underground rhizomes, spreading right under your feet where you least expect it. Mint will climb, crawl, and do whatever it needs to become the dictator of your garden bed, so don’t give it a chance. Some garden experts say you can try to control it by confining it to a container in your garden, so if you need fresh mint in your life, this might be the best way to go. 

Lemon balm (Melissa officinalis) is part of the mint family but has a fresh, lemony scent that adds a little something to salads, soups, and sauces, and can also make a great herbal tea. But, like its mintier cousins, lemon balm won’t be contained, and its aggressive growth tendencies can make it a pain to control in certain areas. It self-seeds easily and spreads via rhizomes, so you’ve got to tackle it from above and below ground. 

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It’s also incredibly hardy and adaptable. So good, in fact, that it escaped its native habitat of southern Europe and naturalized in many of the northern states of the U.S. Save yourself the headache and either put it in solitary confinement (aka a plant pot) or opt for something else. That said, lemon balm is a less aggressive grower than mint, easier to get rid of, and isn’t invasive in all areas. So if you live in a colder region, you might be able to get away with growing it, but be sure to remove the flowers to prevent reseeding (and subsequent weeding).

Amaranth is one of those “if you know it, you know it” plants that aren’t very mainstream, but it’s an ancient genus used by the Aztecs, and may have even been a staple of Thomas Jefferson’s gardens. Some strains are considered grains, others are grown as potherbs or leafy greens in certain countries, and some have ornamental value (we’re partial to the ever-so-goth “Love Lies Bleeding” variety). So, with all of this good stuff, why are we saying you should avoid planting amaranth? Because some of its family members are invasive, and while they can outcompete other weeds, quickly become a problem plant themselves. 

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Redroot pigweed (Amaranthus retroflexus, but often simply called “amaranth”) is a prolific grower that causes devastating crop loss due to its aggressiveness and ability to thrive anywhere. Even ornamental varieties can spread easily (we keep our Love Lies Bleeding in a pot, for the record) and produce lots of seed. These are far less risky to plant, but be aware that you might have to pull out young seedlings each year, which, if you’re looking to reduce weeding, isn’t ideal.