NEVER till Johnson Grass! I was baptized into Johnson Grass 12 years ago this coming December. I had never dealt with it when I lived in California. I moved to OK, and I was like a babe drawn to the slaughter. Previously, Burmuda, had been my most hated enemy in the garden, but Johnson Grass is Burmuda's big hairy ape of a brother, and now I fight them both! I just had the most disasterous garden ever, after growing an entire plot in turnips for two years, and the fallowing same plot for two more. Thought I had got rid of Mr. Johnson Grass, but No, he was trying to get rid of me. I planted an 80x80 Patch of everything from Tomatoes to goji berries, but it was hopeless. The only thing that did well against the Johnson Grass was its nicer, and infinitely more useful cousin milo! I broadcast the milo, and not a Johnson Grass Plant grew there. Seriously considering growing milo on the whole plot next year! Oh and did I mention I made the mistake of Tilling this year!
So lessons I've learned in my fight: 1) NO TILLING EVER 2) If you have clay soil like mine, forget digging it out! 3) Burning it off helps 4) Add calcium to soil. Johnson Grass tends to grow in low calcium soils. 5) Mega mulching works best! The best is sheet mulching like Back To Eden. Heavy cardboard down in Fall, try two inches thick at least. Massive amounts of wood mulch on top, top dressed with lots of manure, grass clippings, hay, straw, leaves and whatever else you can find! More added in Spring, particularly manure. 6)I got a decent squash crop by clipping Johnson Grass shoots with a hand clipper, everytime I saw one. Finally gave up when heat and squash bugs beat me back!!! 7) Early spring plantings are the mainstay! Cool weather crops beat Johnson Grass by being harvested before it gets a foothold. Crops like Fava beans, peas, and the brassicas are fantastically successful!
Consider drip watered containers for tomatoes. They just don't fight the chemicals in Johnson Grass roots well!
Little Bit Farm