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I've got some weeds growing up between the flagstones in our backyard -- is there something natural and okay environmentally that I can use to kill the weeds? Obviously, I don't want anything growing at all there, so it doesn't matter if it kills everything.

An internet search has turned up varied suggestions (vinegar, salt, boiling water) but nothing that seems definitive. Anyone have more concrete advice?

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@Noah, do you want to mix your own (takes a little knowledge, but can be done fairly easily by following recipes found in organic gardening books & websites) or buy an already mixed organic herbicide off the shelf? –  Mike Perry Jul 15 '11 at 23:42

2 Answers 2

up vote 7 down vote accepted

Below are comments (that have now been removed from underneath the original question) I believe contain helpful and useful information that relate directly to the question asked.

@wax eagle comment from above:

For sure don't use salt. Too much salt will make it so nothing grows. But it also dissolves in water and can therefore travel into areas where you do want plants to grow.

Salt also isn't a good answer in your case ie hard landscape, due to erosive effect it can have on concrete, stone, etc. For a drastic image, think about the damage salt (especially old school salt) has on roads, bridges, etc each winter when it's putdown to clear ice & snow.

@Mike Perry comment from above:

Stay away from vinegar based herbicides where concrete, stone, etc will come into contact with it. Why? The acidity in those types of herbicides will eat into the concrete, stone, therefore having a negative affect on them.

Below are 3 organic options that will not have a negative effect on your hard landscape:

  1. Herbicidal soap sprays (a quick internet search will turn up homemade recipes & off the shelf products).
  2. Hand-pulling, cheap (basically free, apart from your time), effective, and very easy to pull them up after a good downpour.
  3. A small propane-powered flame weeder.

If you want to go with a herbicidal soap and would like some more information, report back, and I'll (and I am sure others can/will) add in more information on that option.

Home made Herbicidal soap recipe (for use in a hard landscape):

  • Warm water
  • (Eco-Friendly) Liquid dish detergent, from 0 to 20% (do NOT use dishwasher or hand soap)

Seeing as you are not too concerned about what you kill within the joints of your flagstone, I would start out with a 5 to 10% concentrated mixture, and see if that works (it should do). If it doesn't, you can always mix up a higher concentration and try again.

I would apply the mixture with a spray bottle, so that you can specifically target the weeds you want to get ride of. I personally wouldn't go about just spraying "anyway & everywhere".

Spray the weeds, then 3 or 4 days later go out again and spray them, then again 3 or 4 days after that.

Bear in mind, you will mostly likely have to apply a few application of your mixture before you start seeing any results (hence the above statement).

You might then find, at least for the first year, you will have to go out they and spray your mixture once every 2 or 3 weeks.

But eventually, so long as you keep on top of it, you will most definitely start winning the weed battle. You could end up only having to spray your mixture 2 or 3 times a year (your actual mileage will vary depending on the weeds you have to deal with).

Good luck, and please keep us posted on how it works out for you.

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wow, thanks for the great answers. Yes, I was looking for something I could mix myself -- obviously the salt isn't great for the environment, but I hadn't thought of the effect vinegar would have on the stones. If you have a recipe for the soap spray, I'd love to have it. (I've done the hand-pulling for the last 6 weeks since I moved in, and thought there might be an easier way to prolong the time between....) –  Noah Jul 16 '11 at 4:50

You might try corn gluten meal. It's a natural corn by-product. But there are some caveats:

  1. It won't work against established weeds. It only prevents germination. And in fact it will act as fertilizer for them -- so you'll first need to remove the weeds that are there.

  2. It won't work against perennial weeds. So no help on the dandelions, though it will prevent any seeds that blow in from germinating.

Further reading:

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sorry "corn gluten meal" isn't a good answer in this situation. Yes, "corn gluten meal" suppress the germination of seeds (it is non-selective), but there a number of gotchas to consider when using it. I personally use "corn gluten meal" on my lawn as its Spring time feed & have been reliably informed by the Missouri Botanical Gardens it can take a few years of continuous (recommended) application before seeing results - so far that has proved to be my personal experience. –  Mike Perry Jul 16 '11 at 1:45
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@Mike - Thanks for the feedback. I've seen ok results in garden bed-type applications, but haven't tried hard landscapes. Maybe it's the undisturbed soil? (Would be the same on a lawn.) –  bstpierre Jul 16 '11 at 2:39

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