How much did you put down? My understanding is that it takes quite a bit for it to inhibit germination. I remember reading an excerpt from the original study at ISU and being pretty shocked when I extrapolated the amount they used in the pots to represent lbs per sq ft.

I had a thin layer. It was definitely covering it, though, not just spread across it lightly. I would say that I put down as much as you could expect any homeowner to apply.

I think you have just "busted" the myth of CGM as an effective pre-emergent.

If nothing else, this proved to me that CGM is not a wonder organic product. Perhaps I didn't apply enough. Perhaps I applied too much. Either way, it shouldn't have to be THAT hard to see results. The fact that the CGM tubs grew much more grass tells me that something is wrong. If you didn't know what I was trying to do, you would have declared that CGM was "Miracle Grow."

I don't want to play conspiracy theorist, but since this point has been made here before, I will make it again. Some think that some tests with corn gluten meal might work "long term" (since they usually say results are best after YEARS of applications) because they fertilize the lawn and therefore cause it to fill in thicker than before. As we all know, the thicker the lawn, the more weed-resistant.

I am open to other variations on the experiment. I will be the first to admit that my first shot was less than laboratory conditions. Then again, all of our lawns are less than laboratory conditions.

Before I start this reply, I want to say that I've never used a preemergent of any kind, organic or chemical, so I really don't have a dog in this fight.

I did some reading on this a long time ago, but I never kept the links.

The original research was done in laboratory conditions and they found that CGM applied at pretty high rates acted as a preemergent. I think I've seen 20-40 lbs per 1000 sq ft touted as the rate for CGM, but if I recall correctly, the rates used in the lab were much higher than that. If you used CGM at a lower rate, you'd be providing the fertilizer benefit without the preemergent effect.

If you're open to variations on the experiment, I would suggest calculating the surface area of the test plot and then figuring out how much CGM to apply to be the equivalent of 20 lbs per 1000 sq ft and apply that much. On another test plot, apply at twice that. On another test plot, apply at 4 times the first plot.

I used CGM this spring for the first time. I started organic last summer. I put it down HEAVY, not sure of the rate. I must say I'm disappointed. I have more crabgrass than I've ever had. I mow high, water deep etc. Just my 2 cents. I may go to a synthetic pre-emergent next year. Sorry guys....

As of right now, my plan is to use a synthetic preemergent and then go organic for the rest of the year. I know it is cheating somewhat, but until my grass is SO thick that weeds can't get a foothold, I have to use some outside help.

Last spring ('06) marked my third straight spring of applying CGM at roughly 30-40 lbs per 1,000 sf. All last summer and straight thru last fall I didn't have even ONE blade of crabgrass (If I ever sign on to one of those photo hosting sites I could show you a great picture). This spring ('07) I skipped the CGM (b/c of the 3 year mark and due to cost). Starting about a month ago the crabgrass began to sprout. It is by no means taking over the lawn, but it is definitely intruding and noticeable (and irritating).

I'm not saying this proves or disproves anything. Just my real world experience.

dantis and rutgers1,

I am with you on this one. I switched to completely organic this past year and have had a horrible time with weeds (not just crabgrass). I think for my particular area and grass (SE PA and zoysia) I need a chemical non-organic pre-M to prevent the weeds from getting a jumpstart while my dormant zoysia slowly wakes up. This is definately pretty far north for this type of grass to be present (I purchased the house 3 1/2 years ago), and so the typical pre-M application of CGM probably does more harm than good since existing weeds from the fall get a wonderful fert boost while the grass is still dormant.

I think next spring around the time the forsythia blooms (early-mid march normally) I'll use a chemical pre-M (with NO fertilizer), and then wait until my grass actually needs a fertilizer to switch back to the organic method (probably mid-April or early May). This past year I put down ~25lbs/1000sq ft. of CGM about a week before the forsythia bloomed and probably hurt my goal of a healthy, weed-free lawn.

I'm happy my 1 yr old can play in the front yard without worry of harmful chemicals, but March is still early enough that we shouldn't be outside much in the lawn anyway.

This is my first year organic and I too have plenty of weeds/crabgrass. So I was thinking a pre-emergent wo a chemical also. What would you guys reccommend. BTW Rutgers. Thanks for the test and the results.

You mean without a fertilizer? Pre-M without a chemical wouldn't do much.... :)

I think this is the wrong forum to find out our answer to that question though... :p

But if you find out post it here since I'm very interested. I seem to remember Preen is a commonly recommended Pre-M with no fertilizer (they sell both with and without), but I'm sure there are others that are recommended as well.

"You mean without a fertilizer? Pre-M without a chemical wouldn't do much.... :)"

I think enigma meant without a chemical. Corn Gluten Meal (CGM) has some pre emergent qualities, but some people have had poor results with it. Others have reported good results, but even they say it takes several years.

Three things need to happen for CGM to work properly:

First you need to have the timing down. If your timing is off by a couple of weeks there's a possibility it will not be activated before the first weeds start germinating. These will survive.

Second (as was already mentioned) you need to have a drying period. The CGM will allow the seed to germinate but it will not allow it to form the the tiny hair roots it needs for proper nutrient and water uptake. Without these roots as soon as the plant is stressed it will die.

Third, and this is the most important, you need to have the right set of organisms present in the soil for the CGM to work. Has anyone ever thought why the trials stated it most effective after three years of use? It's due to the repeated bi-yearly cycles of feeding the organisms that allow it to work. Without them the CGM remains just an amendment with lots of protein.

Applied over a three year period, and even sooner if good ACT is used, and applied at 20lbs./k when the forsythia blooms and mid-August (for my area anyway, other warmer climates will have different Fall application schedules), it WILL drastically reduce the number of weeds in your lawn. Others can speculate what they want but the trials weren't set up to be made up. CGM is not a myth.

If you feel compelled to apply chem's to your lawn I believe there's another forum that addresses that, but this isn't it.

Greenjeans