I get asked about corn gluten quite often, so this article will describe it's uses.
Before I do that though, there are several ways you can control weeds on lawns and I've written an entire series of articles about the need for a broad program of fertility and management of the organic lawn to effectively control weeds.
First bit of advice
There is no magic bullet. This product does stop weeds from germinating. It works.
But just like the chemical stuff, if you don't grow a great lawn to stop weeds from starting up again, you're just wasting your money applying anything. The first and most important thing you can do is grow a great lawn.
Applying a weed preventer is only one part of that process.
What is this stuff?
Corn gluten is a by-product of corn milling to make corn useable in baking. It is totally edible and is, in fact, often used in commercial baking. It is also used in a wide variety of commercial food applications.
So it's food grade material that's safe to use an an organic weed control.
How Does It Work?
When a seed germinates, the small root turns and heads for the soil (most weed seeds sit on the surface of the soil - nobody plants them). Corn gluten works almost exactly the way that chemical alternatives do - it stops the root from growing.
So the root hits the soil surface where a layer of corn gluten is waiting and the root stops growing. This pretty much takes care of the weed because if the root can't grow, neither can the top.
How Long Does It Work?
You get about 60 days of totally organic weed control before the corn gluten wears off and disappears back into the soil (to be eaten by microorganisms that in turn make the soil better)
How Can I Make it Work Better
You can make corn gluten work better by thoroughly watering the soil before you apply it and then immediately after you apply it. A moist soil will help the active ingredients spread equally through the garden soil.
Feed and Weed Your Lawn
It also contains 10% nitrogen by weight. This means if you put 20 pounds of the meal on your lawn in the spring, you're applying 2 pounds of nitrogen.
This is all the nitrogen your lawn requires at this time so you can eliminate the use of a spring fertilizer if you use this material to eliminate weed seeds.
If you apply a mid-summer application to control late germinating weeds, you'll have applied 4 pounds of N to the lawn and this is more than enough to feed the average lawn.
What seed does it kill?
It stops darn near any small seed from germinating. Bigger seed such as corn or beans can grow through it but small seed such as dandelion, crab grass (and most vegetable seed so don't think about broadcasting it on the vegetable garden) are killed. It's a superb organic weed control product.
Can I Use it on Flower Beds?
Yes you can because it won't kill existing plants but if you're sowing seed, it will stop flower seeds from germinating as fast as it stops weed seed.
Can I Use it on Vegetable Beds?
The answer is the same as above - but - if you're sowing vegetable seeds, then corn gluten will kill them too (except for the big beans and corn seed that will possibly outgrow the effects)
I wouldn't recommend you use it in the vegetable garden for this reason
Does it Kill Transplants
No - it does not kill vegetable transplants so you can spread it around purchased tomato plants with no problem. It only works on seeds.
Doe it Kill Existing Weeds or Plants?
No, it doesn't kill any existing foliage.
Dangerous to Humans or Pets?
Is it dangerous? Humans have been eating it as a staple food source for a millennium. Need I say more?
What's the downside?
On cold springs it doesn't work as well as warmer springs and in dry years it can have reduced effectiveness as well
Timing of Application
For lawns, you have to time your application of corn gluten and grass seed to avoid each other. As an organic weed and feed for the lawn, I usually recommend spreading the corn gluten in the early spring (that takes care of crab grass and newly germinating dandelions) and spreading grass seed in the fall so it's well established by spring.
For other garden areas, about the same time because that's when a lot of other seeds are germinating but it's not as critical for these areas (remember in the lawn, we're really trying to kill crab grass seedlings)
I normally suggest applying this product when the forsythia bloom
How Much Do I Put On?
Apply 20 pounds per 1000 square feet for best results. Do not skimp trying to save money on organic weed and feed systems by applying it at less than recommended rates, it's penny-wise and pound-foolish (you'll get weeds). But do look for the best deals on it. :-)
Problems with Corn Gluten
You have to water it in thoroughly to get it to spread across the surface of the soil. Failure to water it in is a big cause of disappointment in the product.
Having said that, if it rains a lot in the first two weeks after application, it will be dissolved (so would most chemical applications) and it will be less effective.
In organic soils with high levels of beneficial bacteria (or if you're applying lots of compost) the corn gluten meal will be attacked by the bacteria because it contains 10% nitrogen (nitrogen being a prime food source of bacteria).
So the active time might be somewhat shorter on really good soils. But I note that the better your garden soil- the fewer the weeds you're going to have anyway.