A growing minority of people are becoming more tolerant of weeds. Those who appreciate nature realize certain weeds have admirable qualities. For example, if you can stand to let a little creeping Charlie (Glechoma hederacea) grow in your lawn, you'll be rewarded with attractive flowers and a wonderful aroma whenever you mow. But if you're in the majority, you'd love to kill weeds permanently if you could.
Is It Possible to Kill Weeds Permanently?
"Permanently" is a grandiose word. If there's one thing gardening teaches us, it's humility. Technically, we can answer the question, yes, but we must follow it up with two further questions: What do you mean by "kill weeds," and what price are you willing to pay?
You can kill individual weeds permanently, but not weeds as a class. No plot of open, fertile earth is likely ever to be exempt from having new weeds emerge in it without your continually practicing weed prevention. So, whatever method you used to kill the individual weeds that were already there, you'll have to use that (or an equally effective) method again to kill any new ones that emerge.
Price must be considered on two levels: In terms of killing existing weeds, what kinds of drawbacks are you willing to tolerate? The unwanted effects of chemical herbicides is just one example. And prevention also has its price. Eternal vigilance consumes time and energy.
Methods for Killing Weeds Permanently
Both chemical and natural methods for killing weeds are available. In addition to simple hand-pulling, let's first consider two natural ways to kill weeds:
Soil solarization kills weeds before they have a chance to emerge. It attacks them at the seed stage of the cycle.
To prepare for the procedure, rake the area thoroughly so that nothing sharp is protruding. Moisten the soil. Lay down a clear polyethylene sheet. For soil solarization to work best, you need extended sunny periods, so June or July is a great time. Keep the sheet of plastic in place for two months. The intense heat will cook the weed seeds before they have a chance to sprout.
Soil solarization can be considered "natural" in the sense that no chemicals are introduced to the soil. But there are also natural substances that plants, including weeds, dislike. Salt is one, but the drawbacks are too severe to consider using it. But vinegar is becoming a popular natural herbicide.
Vinegar works best on annuals. Learn when annual weeds set seed and target them before they produce a new generation. Spray when the forecast indicates a sunny period is ahead. Rain would wash off the vinegar before it could take effect. Plus, the real damage to the weeds starts in the days after spraying when the sun hits the leaves. Strong vinegar works best for this as most grocery store vinegars are not strong enough to act as great weed killers. That being said, be mindful of nearby plantings to ensure you do not accidently take out a plant you enjoy!
There are also non-natural methods. The chemicals used can be applied in different ways. For some large, perennial weeds, injection may make the most sense. For example, Japanese knotweed (Polygonum cuspidatum) produces canes large enough that it's easy to inject the needle of an injection tool into them and discharge the herbicide directly into the plant. With non-selective herbicides, this is important: It means you don't have to worry about getting the harmful chemical on surrounding plants you wish to keep.
Spraying Herbicides or Applying Granules
But herbicide is more typically applied in spray or granular form. You're familiar with the latter if you've treated your lawn in spring with a pre-emergent for crabgrass (Digitaria spp.) seed. For existing weeds, you can apply a spray to their foliage (avoid spraying on windy days).
Preventing Weeds Before They Happen
Prevention is the best method, especially if you want to stay natural. Two of the most popular items used in prevention are often used in tandem: landscape fabric and mulch.
Landscape fabric is rolled out across the surface of garden areas where weeds might grow. It acts as a barrier against weeds. To protect your fabric from UV rays, apply mulch on top of it. Mulch can also be used as a standalone product for weed suppression.
Every weed control method has its drawbacks, ranging in seriousness from merely taking up a portion of your time to actually risking health problems. Where you draw the line along this spectrum is a personal matter. To decide if a drawback is a deal-breaker for you, take stock of such factors as your environmental philosophy, health status, and what you plan to grow on your land in the future.
Even applying natural substances can have risks; some are so risky that they're almost never used. For example, while salting a patch of ground in sufficient quantities will kill the weeds there, there's almost no set of circumstances that would justify taking such an extreme approach. One reason why too much salt makes land infertile is that it causes a reduction in the rate and amount of water a plant's roots can draw up out of the soil.
The drawbacks in using chemical herbicides are, of course, legendary, especially when it comes to health. Some chemicals are more dangerous than others. You probably won't be able to acquire the most toxic ones (indicated by a skull and crossbones on the label) without a license.
Nor are all application methods created equal. The drawback of granular applications is that you must broadcast them across a large space, portions of which don't really need it.
A growing concern with the use of herbicides is their negative impact on pollinator populations. If you share this concern, the best methods to use are soil solarization and preventive methods.
Herbicide Options for Managing Common Lawn Weeds in Maryland | University of Maryland Extension.
Basics of Salinity and Sodicity Effects on Soil Physical Properties. Montana State University.
Introduction to Weeds and Herbicides. PennState Extension.