does cornmeal keep weeds from growing

It is high in protein and nitrogen, which can make it a beneficial and natural lawn fertilizer, but corn gluten meal is more commonly used to control weeds. The oily coating on the corn gluten meal doesn’t allow plant roots to form, so newly germinated seedlings die if it is applied at the right time.

Similarly one may ask, does cornmeal stop weeds from growing?

Corn Gluten is a pre-emergent, which is a fancy way of saying that is it is a seed birth-control. Corn meal scattered around an area will keep any seed in that area from growing into a plant. This means a weed seed or a desirable seed. This method is a good option for areas that you plan on planting grown plants in.

Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County

Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your question about cornmeal and weeds. I am going to assume that you mean corn meal gluten (CGM), a by-product of corn starch manufacturing that is marketed to home gardeners for pre-emergent control of weeds, especially in lawns. Yellow corn meal makes great polenta, but won’t do much for weeds!

CGM will have no effect on already-emerged weeds; it only suppresses some seeds’ ability to sprout. It is sometimes used though where only organic herbicides are permitted, but its effectiveness is still questionable. It should not have adverse effects on soil. Because it is high in nitrogen, it could be beneficial if your soil is deficient in that nutrient.