One of the inevitabilities of gardening is the presence of weeds. There are lots of poor weed management approaches out there, many of which have been used for decades. So, I thought it was high time to explore the not-so-wonderful world of weeds, and I invited Dr. Andrew Smith to share his expertise on the subject of managing weeds organically, along with Rodale Institute’s Latest Research, Prevention, and Control.
Drew is a member of the research team at the prestigious Rodale Institute. Not only does he have degrees in agronomy and entomology, but he earned his doctorate in environmental science, focusing on molecular and population ecology. Heady stuff. So when it comes to understanding how to do battle against weeds, Drew is a go-to guy.
What are weeds?
First things first – what you think of as a weed, other gardeners may think of as a desirable plant. Dandelions are a great example. Many homeowners loathe the sight of them, but others enjoy their edible properties. Some gardeners appreciate blooming weeds as an early-season nectar source for pollinators.
All plants play a role in the ecology as a whole. We just might not want certain species to show up in the middle of our lawn or garden. In fact, a weed is defined as just that – a plant out of place. Those plants become a pest – just as some insects are pests, but how we deal with them depends somewhat on our tolerance level.
Most gardeners just don’t like the look of them, but weeds can be more than an aesthetics problem.
Undesired plants on your property are competing with other plants for water, light, and nutrients. Weeds can also harbor or encourage plant diseases. An insect feeding on a weed with bacterial disease can carry the bacteria to your tomato plant or hosta, infecting those plants too. When left unchecked, weeds can reduce airflow around desirable plants and create the stagnant, moist conditions where fungal diseases proliferate.
A weed here and there is nearly inevitable – especially in an organic garden, but we can take steps to prevent weeds from getting out of hand.
Putting the Soil Food Web to Work
It’s true that weeds can create problems for our plants, but scientists have been learning that healthy soil and organic practices can offset or even prevent some issues. The diverse microbial population found in healthy soil works to protect plants from disease infiltration. Soil rich in organic matter and nutrients also strengthens plants, making them less susceptible to disease or pressure from competition.
A study at Penn State University compared the yield of crops grown among weeds in two fields. One field was managed organically, while the other was not. Both fields had been intentionally seeded with the same density of weeds. The study found that the conventionally-managed field produced less. The healthier soil in the organically-managed field counteracted some of the detrimental effects of the weeds, so the crop could continue to produce.
Another study put organically-grown seeds to the test. Seed crops grown by organic methods experience greater weed pressure than seed crops grown in an area treated with an herbicide. The study focused on non-organic and organic oat seeds. Each was grown in containers with weeds and weed-free containers.
The second-generation weed-free oat seed, when grown among weeds, produced only a few seed heads. The seeds from the plants which had been grown among weeds grew well and produced a normal crop of seed heads whether they were grown with weeds or not. It’s thought that plants grown in organic conditions tend to be required to develop some resistance to weed competition. This study leads researchers to believe those plants pass on that resistance to their seeds. My friend Tom Stearns of High Mowing Seeds would probably agree.
What Lies Beneath
Have you ever wondered how those weeds wound up on your property in the first place? Some – like those dreaded dandelions – obviously blew in on the wind. Weed seeds travel for miles on a breeze. They can also be carried by birds or other wildlife – or even water.
Yet even if you could create a barrier against wind and wildlife, weeds would still pop up one place or another in your landscape. According to Drew, weed seeds under the surface of the soil can persist for decades. So, seeds produced by weeds on your property years ago are lurking in the depths, just waiting for an opportunity to spring to life.
Like the seeds of all plants, weed seeds require light and moisture for germination. As long as it remains buried beneath the surface – what Drew calls the “weed seed bank”, the seed won’t be a problem. The less you disturb the soil, the more weed seeds remain buried harmless and asleep under the surface.
When you dig or till, you’re bringing seeds into the light. Sometimes, that can’t be avoided – like when you’re digging a planting hole. Tilling, on the other hand, can be avoided. Although it’s still a right of passage each season for many gardeners, it’s just not necessary, and it can cause more harm than good.
I’ve shared a number of podcasts and videos on the benefits of the no-till approach. So, I encourage you to check those out, but suffice it to say that tilling doesn’t just create more weeds, it also damages the health and structure of your soil.
The no-till approach is so effective against weeds that we filmed an episode of my show, Growing a Greener World®, in the weed-free garden of my friend and fellow gardening expert, Dr. Lee Reich. Lee has been gardening this way for years and rarely finds a weed among his edible and landscape plants.
When it’s easier and better for your garden to avoid disturbing the soil – and it cuts back dramatically on your weed population, what’s not to love about that?
There are other steps you can take to prevent weeds from ever taking hold in your garden. Drew and the folks at Rodale have been working with farmers in what they call a Zero-Sum rain approach to weed management. It’s a principle founded on a goal of never allowing weeds to go to seed.
If a weed germinates somewhere in your landscape, get rid of it before it has a chance to set seed. Even if all you have time for is to cut off the seed head itself, you’ll be making progress. Drew says Rodale’s studies have found that, by preventing weeds from going to seed, the weed population – and the time spent managing it – will plummet.
This is one of the ways my friend, Margaret Roach, approaches weeds too. She manages a large property on her own in upstate New York. She can’t tackle all the weeds at once, so she prioritizes them based on where they are in their reproductive state. It’s the weeds in bloom or forming seed heads that get her attention first. This is the approach I take at the GardenFarm™ too, and it cuts my weed management time significantly.
Zero-Sum rain can apply to your compost too. If you’re a home composter, it’s a good idea to avoid adding weeds which have gone to seed to the heap. You don’t want to go to all the trouble to remove seed heads, only to spread them around your garden when you amend with your compost.
Odds are good that some weed seeds will still make their way into the compost bin, but if you maintain the pile at 140 degrees Fahrenheit (or hotter), the seeds will lose their viability.
Creating a Barrier
The Zero-Sum rain approach doesn’t work for everyone, and Rodale has been working with farmers to study results from other weed prevention or management methods.
Some farms are using what’s referred to as a stale seedbed approach. Fields are tilled with the intent of bringing weed seeds up to the surface. The seeds are allowed to germinate but are removed before they have an opportunity to set new seed.
The use of cover crops prevents weeds by outcompeting them for light, nutrients, and moisture. While some farmers till cover crops into the surface, others wanted to avoid this practice and the weed seeds it inevitably brought to light.
Drew and the staff realized that the no-till farmers were spending quite a bit of time cutting the mature cover crop, baling it, and laying it over the surface of a field before a new crop was planted. Rodale developed what they call a roller-crimper to do the work in one step.
This machine rolls over the cover crop and crimps it at the surface. The crimped stem is no longer able to take up moisture and nutrients, so the cover crop dies in place – forming a natural barrier over the soil. It shades out weed seeds from receiving light for germination and, eventually, breaks down to feed the soil and improve fertility. The field remains weed-free and becomes healthier than the tilled fields as a result.
In our home garden, we don’t need to bring in the heavy equipment to create a soil barrier. We can grow cover crops for the same weed barrier and fertility benefits in our garden beds, but that’s not a viable option for some gardeners. Fortunately, we have an easier option – mulch.
A 2-4” layer of natural mulch over any exposed soil surface will prevent weed germination as it slowly breaks down to add organic matter to the soil. As a bonus – just like the cover crop barrier used by those farmers – the layer of mulch protects your soil against erosion from wind and rain.
Trust me, mulch is simply one of the best things you can do for your garden.
Weed Treatment Options
Mulch is great stuff – really great stuff – but it can’t prevent weeds entirely. Their seeds will still blow in, drop in (thanks to the birds) or hitchhike in on pets or wildlife. In fact, you’re probably bringing in weed seeds too – on your car or your clothes, in your shoes, etc. Trying to eliminate weeds is like trying to stop the flow of water. They will come on relentlessly.
So, what’s the best way to treat them when they do show up? If you’re like me, you avoid chemical treatments. They can be harmful to the soil food web, to my desirable plants, and to the pollinators and other garden visitors. What many conscientious gardeners don’t realize is that organic treatments can cause unintended consequences too.
Just because a product is natural doesn’t mean it’s harmless. Vinegar is a great example of that. It can work as an effective post-emergence weed treatment, but it can do as much damage to surrounding plants. More importantly, it can kill amphibious and other creatures on contact.
Horticultural vinegar is significantly more powerful and dangerous than household vinegar. I recommend against using either on your property. Even when diluted with water, vinegar can be lethal.
Will it kill weeds too? Yes – it can kill the foliage above ground, but it rarely kills the root. So, expect new growth to pop up from that root to cause you more grief. You could achieve the same effect – without the potential harm – by cutting off the top of the weed using shears or a string trimmer. If you keep at it, the lack of foliage will starve the root of energy, and it can eventually die.
Horticultural oils – like garlic, clove or citrus – are sometimes recommended as a post-emergence treatment. Drew says citrus oils can be effective. They work similarly to vinegar. Their acidic property strips the cuticle of the weed, which is what kills the foliage. These oils don’t kill the weed’s root either, but they carry the same risks of damage to desirable plant foliage.
Manuka oil is a new treatment on the market. According to Drew, it has been found to be as effective against weeds as a chemical herbicide, and it’s thought to be fairly safe. I’m looking forward to learning more about this potential option in the war on weeds.
Flame weeders are effective for treating the above-ground growth. Contrary to what you might think, these tools don’t work by burning the weed completely. A light touch of the flame damages the plant’s cell structure. The foliage dies, but you’ll need to treat the weed over and over again as new growth emerges from the root.
Drew says that steam treatment and even electrocution are new options on the market. Electrocution has been shown to kill the root, however there are plenty of risks from that option. How do you zap the weed without zapping the gardener? That detail is still being worked out. For now, this isn’t a good choice for the home garden, but I’ll be on the lookout for advances in safety and practicality.
When you have an area that’s full of weeds, you can let the sun do the zapping for you. Solarization takes a little time, but it’s a safe and effective method for killing weedy areas. An area is solarized when covered with clear plastic which has been sealed against the ground around all the edges. Over a few weeks, the warmth of the sun heats the air and the soil surface trapped underneath the plastic to literally cook weeds to death.
This method works best during the hottest months of the year. It won’t kill weed seeds much deeper than an inch or so beneath the surface, but you could opt to follow up with a layer of black plastic or a black tarp to block the light. That would prevent new weeds from germinating.
Weed Management in the Lawn
Most of the treatments mentioned so far just aren’t practical for your lawn. A good choice for keeping weeds out of your lawn is corn gluten.
It won’t kill existing weeds. Corn gluten works as an effective pre-emergence, inhibiting the germination of weed seeds. As a side benefit, it also provides nutrients to the soil. This option is the safest and best choice for the organic gardener, but it will require some patience. It can take a few seasons for corn gluten to show full effect.
I have a confession. I used to be one of those guys who fought tooth and nail to keep my lawn pristine and weed-free. Over the course of a season, I would devote hours in the pursuit of perfectly-manicured turf, and I was known for doing it very successfully. It only took one mistake with a chemical treatment to show me the harm those conventional lawn products hold.
That mistake is a big reason I became an organic gardener; and why, ever since, I view the occasional weed or two with a little more tolerance. I make sure to go after any culprit before a seed head forms, but I don’t let the imperfect aesthetic get under my skin.
I also mow my lawn at the highest end of its recommended length to shade out weed seeds at the surface. That height also puts less stress on the grass, so it’s better able to outcompete the weeds that do sprout.
Take it from a guy who always prided himself on immaculate turf – a shift away from the traditional norms of lawn care will bring a big improvement in the amount of weeds you’ll see and the time you’ll have to spend managing them.
Get Your Hands Dirty
All in all, the single best weapon against weeds in the home garden is the hand of the gardener. Removing weeds by hand is the most effective and safest option there is. It takes time, but if you combine hand-weeding with other methods – like mulch, no-till and corn gluten – your weed population will decline season after season.
Learn what type of weed you’re dealing with. When you understand how it grows and, more importantly how it reproduces; you can stop it in its tracks. A good garden trowel or soil knife can come in handy to help dig up tap-rooted weeds or cut it off an inch or two under the surface.
When you’re ready to dive even deeper on managing weeds – along with the pests and diseases that make their way into the garden – check out my online course, Master Pests, Diseases, and Weeds. These issues can feel overwhelming, but this class will equip you with the knowledge you need to get ahead of the game. You’ll have lifetime access too, so you can check back season after season – anytime new problems pop up.
Weeding time has become zen time for me. There’s something about pulling weeds early in the morning, when my only company is the birds, that has become one of my favorite garden tasks. That’s especially true just after a rain, when the soil is soft and the roots come up with a satisfying pop. I love every minute of that.
How about you? Are you a lover or a hater of weeding? Let me know which camp you’re in by sharing in the Comments section below. Either way, I hope this episode has given you some new tools for your weed management arsenal. Be sure to listen in by clicking the Play icon in the green bar under the page title too. I think you’ll enjoy my conversation with Drew as much as I did.
Links & Resources
joegardener Online Academy Three popular online courses on gardening fundamentals; managing pests, diseases & weeds; and seed starting!
joegardener Online Academy: Master Pests, Diseases and Weeds – Just $47 for lifetime access!
joegardener Online Academy: Master Seed Starting – My newest online course teaching you how to master the art of starting your own plants from seed and seeding care! Registration closing soon, so don’t miss out!