I had an interesting conversation over dinner with my neighbors about weed control and acidifying soil. Compelling dinner conversation, eh? This morning, I needed to do a bit of research on what we discussed. And I found out a few things. So I thought I’d share.

First, to know if you need to treat your soil, you need to test it. Most resources say to get a test kit from your local Extension, follow the instructions, then send it for testing. There may be many instances where it would be advisable to do this. But for rudimentary testing, I found a handy at-home way to do a quickie test. For general info purposes, here in the PNW, I think this way is sufficient. The information came from National Gardening Association.

At-Home Test

All you’ll need to do this at-home test is white vinegar (the regular stuff you have at home for cleaning, etc.), and baking soda. (Ignore the brands in my photo. I’m not endorsing brands here. These are just what I happen to have on hand at this time.)

Here is what to do:

• Collect 2 tablespoons of the soil you wish to test.
• Split it into 2 parts; in 2 separate containers.

• Leave the soil in one container dry; add a few drops of vinegar. If it fizzes, it means the soil’s pH is greater than 7.5 (which is slightly alkaline).
  • Lime is often applied to turf grass lawn not to make the soil alkaline, but to bring acid soil up to neutral (7.0).
  • Grassland prairie plants like Coneflower and Black-eyed Susan thrive in alkaline soil (though they do great in somewhat acid soil as well).

• Moisten the soil (distilled water will ensure your tap water is not influencing the chemical reaction) in the other container just a bit; add a pinch of baking soda. If it fizzes, it means the soil’s pH is less than 5.0 (which is fairly acid).
  • Blueberries will appreciate a pH of 4.0-5.0.
  • Azaleas, Rhododendrons, Camellias, and Pieris all require acid soil.

Back to Dinner, Vinegar and Weeds

So my friend asked if I was having success using vinegar as a weed killer (read update heading of this previous post for more about vinegar as weed killer). Marginal success, I say. The trick when using vinegar is repetition. Essentially, this is an easier form of killing weeks that doesn’t require bending over and using your hands. But it does require that you hit the weeds over and over again. Some guides say that repeated vinegaring (is that a word? :-) to the same weed will eventually kill it. I can’t tell if that is so. I just know that I see more weeds each time I go out there—particularly in the gravel and concrete cracks. My garden areas where it’s well mulched with leaf mold have virtually NO weeds. But that is another post which you may find informative.

Vinegar-Salt-Soap Weedkiller

I had recently heard or read that adding salt and a bit of dish soap to vinegar made a very effective weed killer. I mentioned that last night, but since I didn’t really know how it worked or what it would do, I thought I’d research it. After a bit of reading this morning, I found this chemical blend indeed will kill weeds. But unfortunately, it hurts (or may hurt) the soil as well. It can render it more or less sterile for 3-6 months (I read a variety of durations). Though that may sound like a good thing—to make an area totally inhospitable to weeds—it’s NOT a good thing for the soil and the ecosystem in general.

I’m not sure if it works like Casoron® (weed killer) which affects the soil to inhibit weed seeds’ germination and rooting ability as opposed to Roundup® which affects the plant tissue (and is supposed to be used ON THE PLANT and NOT on the soil). I am opposed to stuff that destroys soil and it’s microbes — the soil food web — which I believe Roundup® may do in some way if it comes into contact with the soil, but the instructions distinctly say not to get it on the soil; it goes on the plant’s green tissue. From what I’ve read, soil microbes regard vinegar as food, and they can deal with some salt in the soil, but they don’t appreciate (and can be killed by) high salt concentration.

After reading everything, I’m inclined to NOT use the vinegar-salt-soap blend on weeds. It would be too close to Casoron®, and I’m not willing to risk that kind of damage to the soil.

How to End Weeding

The bottom line, I believe—at least in the Pacific Northwest—is that there is no way to END weeding here. We have climate and soil conditions in which weeds thrive. But as I mentioned earlier, that is another post which you may find informative. Even if you use chemicals, eventually, the weeds will be back. Have you ever know ANYone who sprayed their garden with herbicide—just once—and never had another weed? Of course not. So chemicals really don’t end weeding either.

Back to Dinner, Vinegar—and Acidifying the Soil

So we’re still talking about vinegar at dinner. My friend said he applied vinegar to the soil around his blueberries this spring as they were just waking up. We marveled at how a chemical (vinegar) which is damaging if not lethal to the foliar growth of plants can be wonderfully beneficial when used as a soil conditioner.

I have not personally used vinegar to acidify the soil in my garden, but again, I did some reading and find it’s quite common, though an expensive overall solution. Yes, adding vinegar (acetic acid) acidifies the soil. I’m not sure for how long, but my friend says he applies it to his blueberry shrubs every 2-3 years. So it seems that it stays in the soil a good long time. I’d love to hear if others use vinegar like this, and how long it works for you.

Another good way to acidify the soil is to apply elemental sulfur. This is perhaps the most accepted way to gently acidify the soil. You can buy a bag of granulated elemental (or garden) sulfur at your local garden store. And I’m seeing application rates ranging between 2 and 6 lbs per 100 sq. ft. area depending on how much pH reduction you want/need. Repetition may be necessary every 60 days or so. Read the package label.

But back to vinegar. How does that translate into how much vinegar to use? I’ve not been able to find anything very definitive online. Here were what some people said they used:

• 1-2 tablespoons vinegar to 1 gallon water
• 1/2 cup  vinegar to 1 gallon water
• 1 cup  vinegar to 1 gallon water

But no one said exactly how to apply. As in just sprinkle over soil? Saturate soil? How much area will a gallon treat? Is repetition necessary? I’m assuming you sprinkle the mixture in the watering can over your soil without touching the foliage (or I’m assuming anything remotely green or living). And as with the elemental sulfur, from a short ways away from the trunk to out just a bit past the drip line is where to apply on the soil.

If someone has personal experience with more exact numbers and quantities, please post here so we can all learn. I’m not sure why one resource said that using vinegar to acidify the soil was an expensive (or more expensive) option. We need to know the vinegar mixture coverage rate to really make a fair comparison. Anyone want to do that? Please post here. :-)

OK. End of the vinegar lesson for today. Get out there and do that fun test at home. I’ll bet it would be a fun kid science project to do this summer. But what do I know. :-)