Organic Weed Control with Jean-Martin Fortier

Farming with organic weed control requires a bit more attention at crucial times in the growing season, but it doesn't have to mean hours of hand-weeding.

Weeding

Hand-weeding is tiring and time-consuming. Instead, focus on cultivating weed-free plots from the start, and organic weed control becomes a much more reasonable goal.

Photo by Fotolia/Maksud

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Local organic agriculture depends on innovative ideas for its success, and The Market Gardener, (New Society Publishers, 2014) by Jean-Martin Fortier, is full of low-tech, high-yield methods of production proven on the grounds of Les Jardins de la Grelinette. From organic weed control to systematic crop growth and realistic marketing plans, Fortier explains how he and his wife have made a good living on only 1.5 acres of cultivated land. The following excerpt is from chapter 9, "Weed Management."

You can purchase this book from the MOTHER EARTH NEWS store: The Market Gardener.


Too many growers consider hoeing to be a treatment for weeds, and thus they start too late. Hoeing should be understood as a means of prevention. In other words: Don’t weed, cultivate... Large weeds are competition for both the crops and the grower. — Eliot Coleman,

The New Organic Grower, 1989

As the laborious task of transplanting the seedlings into the garden begins to wind down, another job raises its head: weed control. Anyone who has grown a backyard garden knows all too well that vegetables can quickly disappear in a jungle of weeds. So how do you keep a one-acre garden weed-free? And can it be done effectively using hand tools?

Above all, it is important to acknowledge that weeds compete with vegetables for water, nutrients, and growing space. Despite the views advanced in some “natural” gardening circles, the idea that it’s possible to grow beautiful vegetables in harmony with weeds is simply untrue; just as seeking a cropping system that would not require weeding in some form or another is unrealistic.

So-called natural organic herbicides claiming to control weeds may do so in the short term, but they destroy the long-term biological health of the soil. For weed management practices to be both ecological and sustainable, a market gardener should rather look into careful planning for weed prevention and follow with effective and efficient weed control strategies. Dealing with weeds the organic way also takes persistence, the right tools, and innovative techniques.

At Les Jardins de la Grelinette, we tightly space our crop to maximize the yields but also to reduce weed growth. Closely spaced plants growing together quickly form a leafy canopy that shades out weeds. This benefit alone is perhaps the best reason for adopting an intensive approach to growing vegetables. We also work with weed-free compost and have adopted tillage tools that don’t invert the soil. The fact that we transplant as many crops as possible also contributes to keeping our weeds in check. All of these preventive measures help us fend off invasions of garden weeds, yet they are not enough to keep them at bay indefinitely. We do always have to deal with ground popping weeds attempting to take over our crops.

Our primary weed control strategy is pretty simple: hoe the gardens as often as possible and never let weeds in any plot go to seed. This is easier said than done, but focusing on efficiency everywhere else in our operation creates enough time to see this job through. We have also adopted different weeding techniques, here discussed, which make this objective manageable. All in all, keeping our whole garden weed-free is no easy task, of course — especially once the markets begin, and the time available for garden maintenance diminishes at the same time that weed pressure is increasing. But diligence pays off, so the effort is worth it. While weeds still do establish themselves in our gardens, they are noticeably less persistent than in the past. We won’t be declaring a permanent victory any time soon, but each season we can spend less time weeding and more time concentrating on other aspects of the garden. Weeding has even become an enjoyable task.

Cultivating with Hoes

The bigger the weeds get, the more difficult they are to control. Therefore, the most effective way to deal with weeds is to get to them before they get established, at the stage when lightly disturbing the soil is enough to kill them. For the market garden, the best tool for this job is the hoe.

There are many different kinds of hoes and different names for similar tools. Our favorite hoes are long-handled stirrup hoes with a swiveling, double-sided cutting blade. These oscillating hoes (the ones we prefer are Swiss made) cut through weeds just below the soil surface, both on the push-and-pull motion, so hoeing is very fast, efficient, and ergonomic — which over the long run prevents stiffness and bodily wear and tear. We use the narrower stirrup hoes (3-1/4 inches) for crops planted in four or five rows per bed and the wider ones (5 inches) for crops grown in two or three rows. We also use a wheel hoe with a very wide blade (12 inches) to hoe crops grown in just one row and to weed the pathways. In addition to stirrup hoes, we also use the collinear hoe developed by Eliot Coleman. This tool is useful for weeding mature crops because its blade can reach right around the base of the plant stems without damaging the leaves.

In an ideal maintenance schedule, gardens are hoed every 10 to 15 days, especially during the months of June and July, when weeds are persistent and in direct competition with crops. It’s also important to cultivate under good circumstances; if the soil is wet, any weeds hoed may re-root and the job will have accomplished little. The best time is on a dry, sunny day — and so that’s when we plan this chore. In times of prolonged wet weather, it may be tempting to go out and cultivate anyway, but we’ve learned that it serves no purpose. One might as well advance other jobs ahead of time and be ready when the sun comes out. We’ve also learned to keep our hoes well sharpened. Doing so makes a big difference in terms of efficiency, especially when hoeing perennial weeds past the cotyledon stage. You want the hoe not only to disturb the weed, but to slice the roots of the uprooted plants. We sharpen our blades once a week with an electric grinder and carry a handheld carbide sharpener (the best hoe-sharpening tool we have come across) with us to the garden when cultivating.

Many people have trouble believing that weeding with hand tools is efficient and productive on a commercial scale, but we can vouch for this low-tech approach. With a good hoe and some practice, a market gardener can become very agile and swiftly cultivate the soil without damaging the crops. The flexibility afforded by manual hoeing is the main reason why we are able to space our crops, not according to standardized weeding implements, but however tightly we want to space them. The tools adjust to our practice, they don’t define it.

But beyond the goal of eliminating weeds, spending time hoeing the crops also allows for an intimate contact with the soil and the vegetables. I find that this chore helps us get a good feel for what is happening in the garden, encouraging the development of botanical acuteness and sensitivity. Over many years, I have been able to watch vegetables go through every stage of development — and have learned a lot about plant biology in the process. All things considered, I believe hand hoeing not to be a step backward, but a simple and appropriate tool for the needs of a market garden. I have never envied vegetable growers who use mechanical weeding techniques, nor have I tried to find a better way to cultivate.

Weeding with Tarps

The main factor in keeping a garden weed-free is how much space is to be kept under control. Our 10 plots have a total area of 1-1/2 acres, and if we had to cultivate the whole garden every week, I doubt we would manage. This is where the opaque UV-treated tarps come in handy. Not only are they useful for smothering weedy ground and preparing the soil before planting, but when covering unused beds, the tarp limits the surface area on which weeds can establish themselves. Even more interestingly, we have also observed that black tarps do an especially good job of diminishing weed pressure on subsequent crops. The explanation is simple: weeds germinate in the warm, moist conditions created by the tarp but are then killed by the absence of light. This weeding technique, described as “occultation,” is widely use by organic growers in Europe.

We have been using 6 mm black silage tarps in the garden for almost a decade now, and I can say without hesitation that their usefulness is one of the reasons behind the overall success of our operation. This passive and efficient practice takes care of part of the weeding chores while we are getting work done elsewhere in the garden. Besides being a petroleum product, the only difficulty we face using these bulky tarps is that they are heavy to move around. Our solution to this has been to buy more of them every year, with the intended goal of having one for every plot, thus eliminating the need to carry them from one garden to another. This minor challenge aside, the overall advantages far outweigh the drawbacks.

The Stale Seedbed Technique

The stale seedbed technique (also called false seed planting) consists of preparing seedbeds a few weeks prior to the seeding date, allowing weed seeds in the top 2 inches of the soil to germinate. When ready to seed, whether directly or by transplanting, the soil surface is then shallowly worked again, effectively destroying emerging weeds. The result is that the crop can get a head start over the weeds yet to come, and the difference between beds that have received the treatment and those that have not is striking.

For this technique to be effective, a few things must be considered. Firstly, it’s important to let the beds go stale long enough for the weed seeds to germinate. In our gardens, we prepare them 10 to 15 days in advance and cover the bed with floating row covers. Secondly, the destruction of the emerging weeds must be done in such a way as to not bring up weed seeds that haven’t germinated. A quick surface passage with our power harrow does a great job, but using a wheel hoe works just as well. To avoid any stirring of the soil and guarantee that buried weed seeds will not come up, a flame-weeder can also be used.

Since this simple technique gives tangible results, we try to use it as much as possible, especially for direct-seeded crops. To ensure proper results, we have systemized the practice by integrating bed preparation into our crop planning calendar. This isn’t always possible for early spring seedings, and it doesn’t always work out according to plan. For instance, double cropping doesn’t always allow for an extra two weeks between both plantings, but adding it to our weekly schedules whenever possible certainly helps.

The stale seedbed technique is mandatory for our mesclun mix crop. When seeded at such a high density, this crop leaves almost no room for hoeing. We therefore plan to seed this salad mix every two weeks on new beds, leaving us enough time to effectively stale the seedbeds. We pay just as much attention to our false seedbeds as we do to the mesclun mix since we want to ensure optimal growth in both cases. We irrigate the weeds as needed and protect them with floating row covers to keep the soil moist at all times. When you think about how much easier it then is to harvest a weed-free crop of mesclun mix, growing a thick carpet of weeds can be almost as satisfying as growing the greens themselves.

Flame Weeding

Flame weeding is a technique in which weeds are killed by burning them with a blowtorch. Actually, the term “burning” is a bit misleading: the weeds are not burned to a crisp but rather subjected to a form of heat shock that causes damage at the cellular level. In order for flame weeding to be successful, two conditions must be present: the flames of the torch must actually make contact with the soil, and the weeds must be small enough that a single second of flame exposure is enough to kill them (i.e., between the cotyledon stage and the first true leaf). It’s also important to flame over a very smooth seedbed, since irregularities in the surface of the soil can sometimes deflect heat from the flame weeder, giving some protection to weed seedlings.

Flame weeding nicely complements the stale seedbed technique. Burning the weeds avoids the need for the stirring action of a harrow, thus preventing buried seeds from being worked up to the surface. However, we rely on flame weeding mostly for burning weeds in the pre-emergence stage of direct-seeded crops. This approach is somewhat like the stale seedbed technique: seedbeds are prepared 2 weeks in advance to give weeds a head start, but instead of seeding after the destruction of the weeds, you seed into the stale bed halfway through the process. Then, just before the vegetable plants emerge from the soil, the flame weeder is run over the ground, leaving the crop to emerge into an essentially weed-free bed.

Pre-emergence burning is the ultimate way of providing weed-free beds for slow germinating crops that are direct seeded such as carrots, beets, and parsnips. However, this technique must be practiced with diligence. If you wait too long to burn the weeds and the vegetable begins to emerge, the vegetable crop will be totally invaded by weeds. If this happens, you will need to spend many hours weeding by hand or quite possibly have to reseed altogether, thus delaying the crop by a few weeks. To avoid missing the boat, we always throw on a handful of seeds that are known to germinate earlier than the main crop at the head of the seedbed. A patch of tiny radish plants signals that beets are about to pop up, while tiny beet tips indicate that the carrot crop is imminent. The appearance of the indicator crop tells us exactly when to flame weed so that we can do so with confidence. We also make sure to write a note on our crop calendar to remind us to check on the plants five days after the main crops have been direct-seeded. It’s better to burn too early than too late.

Mulching

Mulching the garden with soil-covering material is another great way to keep weeds under control. Many home gardening books extol the virtues of using organic material such as straw, leaves, wood shavings, cardboard, etc. as ideal mulching material, but my experience leads me to advise against relying on them. Not only does plant-based mulch cover attract slugs, but weeds always seem to find their way up through them. This means you still have to weed — and weed by hand, because the mulch makes hoeing impossible. On a commercial scale, the cost and time required to spread thick amounts of organic mulch are too high, in my view. The one plant-based mulch cover that doesn’t have all this inconvenience is grass clippings. We can easily produce it onsite (we mow our headways every other week), and its fine texture makes it easily digestible by soil organisms in the event that hoeing is required and we have to mix it into the soil. We’ve had interesting results working with 1/2-inch grass clipping mulches, but not to the extent of making it a systematic measure for weed control.

We’ve always found inorganic mulches to be more effective. We rely on both landscape fabric and biodegradable film to cover the beds of certain vegetables that stay in the garden for a long time, such as tomatoes, peppers, zucchinis, and melons. These mulches not only smother weeds, but also provide a highly beneficial environment for these crops, which prefer hot and humid conditions.

Both products have their advantages and disadvantages.

Landscape fabric (we refer to it as “geotextile”) is reusable and durable. Ours are in their sixth season and show little or no wear. They come in rolls of a width that will cover both beds and pathways — we use 16-foot-wide rolls that can cover 4 beds — and into which we’ve burned round holes according to the crop we intend to cover, in our case eggplants and melons. To make the holes, we use a small propane torch (it works best with a fine-tipped nozzle). We locate the holes by following a plywood template of the proper spacing. Burning more than 100 holes in such a way is a messy job (it almost made us reconsider this approach...), but once done, the work remains useful for many years to come. If landscape fabric is cut, the new ends should be burned to avoid unraveling of the fabric. Be sure to purchase a professional grade of landscape cloth, since the thickness of the fabric and tightness of the weave will affect how long it lasts.

The biodegradable plastic film that we also rely upon is a lot less expensive and more versatile, as it allows us to punch holes at any desired spacing. The one we use is 100% biodegradable and made of compostable genetically unmodified cornstarch resin. Since it leaves no toxic residue, we can mix it into the soil with a clear conscience at the end of the season. It comes in a 500-foot roll and is 36 inches wide, which is enough to bury the edge and still cover the width of our 30-inch beds. Although this plastic mulch is relatively fragile, we still prefer it to conventional plastic mulch, which ends up in the garbage after the crop has been harvested.

Organic Weed Control Technology

I believe too many growers emphasize mechanical weed control as the solution to their weed problems. Most of the organic vegetable producers I know are always looking out for new cultivating tools: finger weeders, flex tine harrow weeders, torsion weeders, computer-controlled, and even robot cultivators (for real!). Upon first glance, it seems that having all of these tools or machines would be ideal, given that each one works precisely and effectively under very specific field conditions. Trade shows I attend are always lined up with growers eager to acquire new technologies for their farms. For the market gardener, such sophisticated tools are not currently available (at least not to my knowledge), and this might be a good thing as it enables us to look elsewhere for weed control solutions.

I have laid out different techniques that help protect our gardens from weed invasions. Intensive spacing, transplanting, not turning the soil, never letting weeds go to seed, making sure not to import weed seeds from manure and mulches, and depleting the seed bank by stimulating germination are all solutions that are basically cost free. They do require, however, forethought and reflection in the planning and organizing stages of the cropping system. I firmly believe this is where a market gardener should concentrate his or her focus in order to effectively deal with the weeds in the garden. It’s also important to understand and apply the difference between weeding and cultivating.

I was once at an organic farming conference where an experienced grower with more than 20 seasons under his belt was asked to name the top five most problematic weeds on his farm. After quickly naming two, he stalled for some time, causing an awkward silence in the room. After a few moments, he admitted that he didn’t know the names of his weeds because he never let them grow big enough to make them out. I thought that said it all.


Further Tips for Organic Weed Control

Don’t Turn the Soil Over When You Can Avoid It

Every square inch of your garden contains weed seeds, but only those in the top inch or two of soil get enough light to trigger germination. Rototilling and digging brings hidden weed seeds to the surface. If you need to invert the soil, then be prepared for an invasion of weeds about a month later!

Soil Solarization

You can let the sun help you get rid of weeds by leaving clear plastic in place for 6 weeks during the summer. This is an effective strategy for depleting the seed bank and is a solution for weed management in hoophouses, or during early spring planting when stale seed bed techniques are not possible. Aside from requiring beds to be free during the growing season, the main drawback of this technique is that you don’t destroy only weed seeds, but soil organisms and microbial life in the garden as well. Under certain circumstances, however, such an effective strategy is worthwhile.

Straw Mulch

Mulching with straw can be problematic. Most grain farmers who sell straw use herbicides to control weeds in their fields. This means straw mulch can carry herbicidal residues into your garden. Unfortunately, organic straw is hard to find in some areas—and if you find it, it may contain large amounts of weed seeds that you’ll be importing into your garden. The straw we use to cover our garlic during the winter is made from first-cut fall rye. This straw is harvested at the beginning of the summer, when few weeds have gone to flower; it’s therefore more likely to be clean and free of herbicides, even if produced by a conventional farmer.


Reprinted with permission from The Market Gardener: A Successful Grower’s Handbook for Small-Scale Organic Gardening by Jean-Martin Fortier and published by New Society Publishers, 2014. Buy this book from our store: The Market Gardener.