Vinegar Herbicide Update

So it's been 10 days since I sprayed the 30% vinegar. Initially I got a good response. Everything turned brown. But I was curious about the long term effects. I've got my answer......

Two classification of my weeds really died back, almost 100%-- certain tender type grasses and all non-grass weeds (excepting honohono, which I will discuss later). To date, these haven't shown signs of growing back. But the mature, aggressive tropical grasses are now sending out new leaves and new shots (kikuyu grass, St. Augustine grass, hilo grass, and bermuda grass). I didn't spray any molasses or california grasses, so I have nothing to report.  I'm not surprised by this. Some tropical grasses are ultra tough. Also of note, all the mosses on the concrete walkway are totally dead. 

No grass regrowth and the tender young honohono grass is dead.
Only the weeds that I failed to spray show any green color.

A couple of people have voiced concern about the vinegar changing the soil pH. I was curious about that too. First keep in mind that I didn't saturate the soil with vinegar. I simply wet the leaf surface. I didn't even spray enough that the vinegar was dripping off the leaves. So today I tested the soil. To date there has been no change in the soil pH. In a way I wasn't surprised. You see, I live downwind from a volcano that has been spewing SO2 for decades, which results in acidic rain. The two of those years most recently, my rain pH has been fluctuating between 4 and 6. Even with this, my soil pH hasn't changed much, most likely due to the constant decomposition of organic material in the soil and the availability of calcium carbonate (via bone and coral sand added to the compost). All those soil microbes and compost help moderate the soil pH.

This area completely browned out, but it's starting
to show some green. 

New grass leaves....a variety that I don't know the name of.
Lots of brown dead leaves in this photo. 

The before photo, where the St Augustine grass
was burned brown by the vinegar. 

The St Augustine grass is growing new shoots. 

The mature tropical grasses survived the initial spraying of 30% vinegar. But I bet that timely repeated spraying would cause the plant to run out of energy and die back. Timeliness is probably the key. In my own situation, I have another weapon.....mulch. After spraying the vinegar, I will be applying a layer of fresh mulch. That will help prevent the grasses from growing back. And any that put up shoots through the mulch will get resprayed and remulched. I think I've hit upon a way to control most of my weeds in the gardens. Now my next experiment will be on that dratted bermuda grass! I have a gut feeling that bermuda grass isn't going to be that easy to vanquish. We shall see. 

Now for honohono. The spray quickly killed the leaves. And the tender non-rooted tips also died. But some, not all, of the mature rooted stems survived. I plan to spray any new growth that I see. And I'm guessing that the honohono grass will be defeated! Again, we shall see.

No regrowth where it was sprayed.