Thanks for your additional options

Is glyphosate organic? I am in the organic section of the garden so I have to only use OMRI products

The people directly around me are good about keeping weeds short. This year i'm going to buy a string trimmer to keep cutting it down.

Glyphosate is NOT organic and if you are restricted in your products then this is a big no-no!

I think your best options are either solarization or smothering. FWIW, solarization is best effected by using clear plastic sheeting, not the blue tarps. The clear intensifies the sunlight into considerable heat and it is the heat you want to "cook" the weeds or Johnson grass away. Black plastic should work as well, as it also collects and retains heat.

Both of these processes take time, however - 4-6 weeks of pretty much unobstructed sunlight for the solarization and several months to a full growing season for the smothering with cardboard. Since now is not an ideal time of year in your area to attempt either, you may get a very late start to your planting season or miss it altogether, although for future growing success, weed control may well take priority.

When I first took over my allotment over 25 years ago it was entirely full of couch grass, which I imagine is similar to Johnson grass. I dug the whole plot deeply and thoroughly over a period of two years. Sometimes I was only achieving one row in a whole hour's digging. The areas I wasn't working on were covered with black plastic or old carpet (now frowned upon) to eliminate light. Under the plastic all annuals and many perennials died off. It took ages but it worked and no chemicals were involved. Since then the plot has needed only shallow cultivation or none at all.

Not to complicate the issue, but if I may I ask; how big is the entire community garden?

I'm curious because 20' x 60' is a fairly-large size piece. Is it expensive? Wouldn't everyone be facing the same deer problem? I wonder if everyone would chip in, if a fence surrounding the whole garden wouldn't be more cost effective... as well as having everyone share in the work.

I would till the entire space, remove as much of the grass as possible, and mulch it thickly. Instead of compost (would require quite a bit) I would get straw, leaves, grass clippings, wood chips, and whatever other organic matter I could find to mulch about 6" - 8" deep. Yes, the grass can survive under that much mulch, but it will be hindered and it will keep it from getting away from you like last year.

As you clear the grass, move the thicker of the mulch to the uncleared areas - leaving at least 2" and preferably about 4". If you can collect enough mixed organic materials, keep it 6" - 8" thick. By the end of the season the mulch will be a lot less thick, and your soil will be the better for the effort. The grass under the thick mulch will pull much easier than from bare, dry soil.

Using this method it can take a few years to clear grass from land under production, but you won't lose any time. You won't get it all the first (or 2nd, maybe 3rd lol) year without TOTAL devotion to the task, and I don't know about you, but I like to eat and sleep now and again.

I wouldn't till the soil. That is likely to make the grass problem worse if the grass is anything like the Bermuda Grass that grows in my garden. All of the roots you chop off will be mixed into the soil then germinate and grow along with the weed seeds you bring to the surface. I found that out the hard way in my community garden plot. I was new to gardening and tilled everything into my soil and when I was finished my garden looked weedless and I thought, okay no more weeds, now to plant. In a week or so and after I had planted a few tomatoes and squash, my garden was a huge weed patch, much worse then it had been, and I could not keep up with the weeds even if I weeded every day for hours, which of course I did not have time to do. You have a nice big plot by the way, mine is 15' by 30'. If it were my plot I would thoroughly weed small areas at a time and make raised beds of soil where you can plant seeds or plants starting with your earliest vegetables and so on. Cover the rest with a thick layer of cardboard or a heavy plastic or both, until all the grass is killed. Apparently, you can cut holes in the cardboard or plastic and plant plants as well but I've never done that. The deer problem is difficult. A 6ft fence would keep them out more or less but in the meantime you could get light weight mesh cloth or agri-cloth and tent your crops. Make sure the stakes and cloth are secure and the deer might move on if they can't easily get your plants. I use tulle cloth from the fabric store, just make sure to leave an opening or two so pollinating insects can get to your plants that aren't self pollinating. Garden centers sell black mesh to keep deer out but I don't like it since it tangles and they seem to be able to get through it anyway. I know it does seem like a big expense and is taking you a lot of time and energy but after a few seasons of growing and improving the structure of your garden the hard work will be done.... Just work on small areas at a time so it doesn't get to be too big of a job.

Johnson grass spreads by its rhizomes and tilling just makes more of them to produce more grass, tilling the soil is not a way to control Johnson grass.

Glyphosate products are not acceptable to any organic grower.

Cardboard, or newspaper, may inhibit the growth for a year but then there will be those rhizomes that will produce new plants next year, been there, done that.

Solarizing might work, for a year or two. However, solarizing must be done with clear plastic sheeting, not an opaque material, so the sunlight reaches the soil to heat it up.

A video produced by PBS Nature, "The Private Life of Deer", shows the buggers jumping a 9 foot fence.

The only truly effective method of controlling Johnson Grass, Quack Grass (aka Couch Grass) or other similar invasive grasses is to dig out their rhizomes, every bit and piece. I have gardened with the stuff by staking out an area to work on removing the rhizomes each year and covering the remaining parts of the bed with newspaper, or cardboard to suppress the growth and moving that section to be dug each year until the whole bed was dug. It takes time.

kimmq is kimmsr

I agree with kimmq. I am very aware that how rhizomatous grasses increase. But I can only describe what has worked for me on an allotment I have gardened for over a quarter of a century. The key is that the initial digging has to be clinically thorough. 'All of the roots you chop off will be mixed into the soil ...' Not if you don't chop any. I use a garden fork, not a spade, so nothing gets chopped. Every forkful of soil is sifted through the tines and every root is picked out by hand. It has to be slow, methodical and thorough. But it really does work. Kimmq's technique of covering the areas you are not working on is also what I did. But I used black plastic and old carpet which purists would frown upon. Cardboard disappears in my wet climate too fast, although I do use it now the soil is clear of couch.

I am not entirely sure what the term 'tilling' means in US English. It appears to cover everything from ploughing to hand digging with a shovel. Certainly tilling with a rotavator is disastrous with such grasses. But hand digging works if combined with removal of every rhizome.

I asked some local growers - Johnson Grass spreads by rhizomes, so chopping it up or tilling in a cover crop just spreads it around - it's not as aggressive that way as bermuda grass but it's persistent.

It is CRITICAL to keep the tops from doing what yours
did, which is thrive and set seed. In fertile uncompacted soil, you have tertiary
roots 20-30 inches down which are capable of sending up sprouts all
summer.

The vineyards use geese, which may be organic as heck, but impractical in a shared garden. They leave NOTHING behind that they think is edible.

A "flame weeder" might work if you repeatedly use it on the new sprouts - the idea is to exhaust the root's stores of energy by forcing them to grow leaves faster than the leaves can resupply the roots storage.

====================

This OLD research explains the root development cycle and where to interrupt it:

http://naldc.nal.usda.gov/download/ORC00000094/PDF

They are in favor of repeated SHALLOW cultivation to force the roots to resprout to the point of exhaustion, and even (if you have repeated freeze-thaw cycles) shallow cultuvation in winter to expose and freeze the roots.

They are also in favor of close mowing or grazing to keep the plants too small to support the big, deep problem roots, what they call the tertiary roots. =========================

If you are in the "organic" section, that limits your chemical options. You might kill it with repeated applications of "horticultural" vinegar (the 20% stuff, or a minimum of 10%) but it's nasty to use. Be sure to read the MSDS and wear appropriate skin, eye and lung protection.

http://www.groworganic.com/organic-gardening/articles/help-johnson-grass 

http://www.gardenguides.com/139610-organic-control-johnson-grass.html

They claim this works: http://www.homedepot.com/p/Avenger-Weed-Killer-128-oz-Organic-Weed-Killer-Herbicide-Concentrated-AVGR-Conct-128oz/204336249

NOTE: the "organic" solution you see on Pinterest and other blogs, with vinegar, dish soap and salt is really bad for your soil and doesn't work worth a darn.

"I am not entirely sure what the term 'tilling' means in US English. It
appears to cover everything from ploughing to hand digging with a
shovel."

Yeah... unfortunately it's true, I can be a bit too lazy with my language. I often use 'till' interchangeably with 'turn'.

Then again, I'm also too lazy (read: old :-P ) to think about fork-turning a 20' x 60' plot that doesn't belong to me, and will never belong to me. How much effort would I put into a space that I was paying for season to season? Anything can happen, and that much work to clear that much land is a serious investment in time, energy, and fallow land.

There's no way I would pay for an unproductive garden spot. There are many ways to skin the cat, but above you have the basics. Get the soil turned, tilled --- friable... in any way you can. Mulch it in any efficient, effective, and organic manner possible. Plant it, and consider the weeding an on-going effort. Either that or find another (rhizome-free) space to rent.

As far as the weeds - keep 'em mulched, keep 'em managed, work at ridding them, and learn to live with them. The worst... is that in a shared space, even as you battle to not let seeds form... will your ever-changing neighbors be that diligent?

You expressed a desire to go 'no-till' (which often, also means 'no-turn')... get organic matter into that soil and you'll soon be able to move in that direction.

Thanks everyone for your comments!

Tilling soil is to plow, turn, harrow, cultivate, or otherwise work the soil to ready it for planting.

kimmq is kimmsr

kimmq - I do understand that. But the term is non-specific and it is not possible to tell the precise operation. In my brand of English 'tilling' specifically means cultivating with machinery. So when people in these forums talk about 'tilling' their gardens I still don't know what exactly they mean unless they specify the method. My garden has never been tilled but it has been dug.

The difference between English English and American English. The meanings are the same but different.

kimmq is kimmsr

Last spring I was asked to oversee a community garden with similar problems. Deer, woodchuck damage and heavy weed growth had discouraged ardent gardeners from renting plots. During last summer's growing period I studied the situation, renting one of the plots to try some experiments. We are dealing with nut grass which is a major problem, also. An easy way to solve the problem is to weed whack the weed growth, spread a layer of landscape fabric, which is permeable, over the bed securing it with bricks and then cover the cloth with a fine pine bark mulch known as soil conditioner. Some weeds will sprout through but are easy to control. And then, for several years only plant 'starts' that you can insert through slits in the fabric, adding a starter fertilizer to each as you plant. Then set up an organic liquid spray schedule.

Take advantage of the permeability of landscape fabric to spread compost, fertilizers and liquid fertilizers over the fabric. This leaves the soil beneath undisturbed, encouraging development of various beneficials.

Also, look for a paper product named Weed-Ex. 125' rolls. Expensive! Look for bargains at one of box stores in garden department. Use this as a single layer under a layer of landscape fabric for stubborn weed growth. Those growing in raised box gardens can use just one layer by itself to plant through and also to install in late fall. Great weed stopping product for some situations. Really works. Again, cover the paper with a soil conditioner product which can be worked into the soil later.

The paper and/or landscape fabric will create ideal conditions for invasive grass species like Johnson and Quack (Couch) grass to grow and spread. Been there, done that.

kimmq is kimmsr

Your answer was expected, Kim. Have you honestly tried installing Weed-Ex paper first, then covering it with landscape fabric and soil conditioner mulch? This method is working for us. I would encourage our OP to try the method on a garden section.

Nandina, if you have ever had to deal with Johnson and Quack grass, as
I have, you would know what I am talking abou8t. The only way to eliminate these invasive grasses is to dig themj out.

Been there, done that.

kimmq is kimmsr