Corn MEAL does not act as a pre-emergent herbicide. That's the job of corn GLUTEN. Corn meal has fungicidal properties.

Thanks guys. I've been confused about this Preen stuff and was afraid to ask and look dumb.

Now I got to go research corn GLUTEN. I didn't know that was different than using corn meal.

You've probably saved me time and $$$$.

Huge thanks. :)

Don't forget that gluten is an integral part of the corn seed. The seed must be specifically milled to remove the gluten; often done during the same process which removes the oil.

As I accidentally learned, if you use *whole* ground corn, there will be pre-emergent properties as well as the anti-fungal properties. I don't want to say how long it took me to figure out *why* the roses didn't need weeding!! But I did carry the idea onward and mid-summer treated a portion of the 'lawn' (which was quite filled with dandelions and other weedy annuals) with whole corn meal. The following year found only a couple dandelions in that area. During one early spring, DH used the whole meal slightly uphill from the veg garden, only to discover later that *none* of the spinach or lettuce sprouted in the rows closest to the mealed area. I would guess that some of the meal washed downhill during a heavy rain, and the preemergent effect remained in the garden soil long enough to affect the mid-spring sowing; it did not affect nearby transplants. I have been using whole ground corn on the lawn for the past three years now, and have almost forgotten what it is like to dig up dandelions, in spite of being surrounded by the neighbors' untreated (read dandelion-filled) lawns.

How long must one wait after spreading pre-emergent before planting seeds? Days? Weeks? Or can't it be done at all? Does one have to make a choice between planting seeds in the garden and having to weed by hand - or having a weed free garden and only using transplants?

Also does one put down pre-emergent and then wait a while and then plant the seeds or plant seeds and then when they sprout put down pre-emergent?

bud_wi - Waiting period depends on which pre-emergent you use; commercial ones will have the info on the label; just remember that no chemical knows the difference between a sprout you want and a sprout that you don't want. A lot of time variance is caused by climate - days of rain or heavy irrigation can shorten the length of time the preemergent is effect, vice versa, a long dry spell can extend the time. For CGM, the recommended wait period (before seeding) is usually 4 to 6 weeks - that's the period the gluten is effective. I use whole cornmeal only on already sprouted lawns, but from DH's experiences I would guess it has the timeframe as commercial CGM.

One either waits until the seeds sprout before using the preemergent, or waits until the chemically effective period is past. The point of the pre-emergent is to prevent seeds from sprouting, irregardless of whether you want that seed to sprout or not.

And re weeds in the garden, I'd recommend using any organic mulch -which would give you both a superb weed-barrier and *improve* the soil; all without worries about what chemical pollution may be doing to the environment. A variation of lasagna-gardening works marvelously to keep the areas weed-free: put down 10 to 20 overlapping sheets (or up to 1/4") of sopping wet newspaper and cover all visible paper with 2" shredded leaves or 5-6" straw or hay or 2-4" mown grass or whatever is handy that will decompose. The paper smothers the weeds; the mulch prevents the paper from wicking moisture - and looks nicer; and the worms will be thrilled and they leave castings which your plants will adore. I mulch all paths heavily, leaving rows or beds open until the seedlings are about 4" tall, when I then tuck mulch around each plant. Tomatoes and peppers get the path
lasagna to within an inch of the stem; carrots, lettuce and similar bedders get dry shredded leaves sprinkled over them weekly (I just run my hand across the plant tops to uncover them and brush the dry leaves to the soil). Beans seem to be very fond of lasagna so I plant them in high-hilled rows and make an on-going lasagna with paper and mowings in the paths between rows. And I rarely have a weedling to pull.

Thanks. I think I got it. Knowing corn meal has the 4-6 weeks is VERY helpful.

This is all great info...my follow up question is this:
I put down wildflower seeds and then put preen weed preventer on the soil immediately after. I know now after reading the directions that I was not supposed to do this. oops! However, I was wondering if anyone knows whether or not my seeds are now destroyed. Will the seeds sprout after the preen has worn off after several weeks or will I have to put down new seed>?

The seeds you put in already with the Preen won't sprout. You probably have to use transplants now.