I like weeding. Well, I like it for about the first five minutes . . . and I like the part where I dump the bucket out in the chicken pen and they have a feeding frenzy over the grass and dandelions. I also like how the finished bed looks – especially after a topdressing of compost. It’s that in-between part I don’t care for: all that kneeling, scrabbling, yanking, cursing at the tap roots that break off just below the soil surface. It’s pretty cold out there this time of year, even in the sunshine, and the soil isn’t warming up too quickly because it’s been typically wet, so I end up with numb fingertips despite my rubber-coated gloves. And while I enjoy triumphing over the really tough weeds (like those damn mallows the previous occupant let loose) weeding by shovel is not my idea of a good time.
I’m sure any gardener is interested in having another tool in their weed-fighting arsenal. I’m an organic gardener, so I won’t touch the pre- or post-emergence herbicides with all the scary warning labels. On top of being so toxic as to be an overwhelming case of overkill, they are usually indiscriminate killers, so if you are trying to sneak in a little weeding this early in the year you can kiss this summer’s columbines and foxgloves goodbye before they’ve even surfaced. What I use instead is corn gluten meal.
Corn gluten meal, a by-product of corn processing, works as a pre-emergence weed control by suppressing germination of most seeds. The Wikipedia article explains it thus: “Proteins in CGM inhibit root formation on newly-germinated seeds, killing the plant. Applications must be timed so that the CGM is present and effective as seeds are germinating.” It also recommends applying corn gluten meal “at least 6 weeks before sowing, or 2 weeks afterwards.” This stuff is completely harmless; it has been traditionally used as animal feed and can even be consumed by humans (although I am given to understand that it is “unpalatable”). As it breaks down it leaves behind some nitrogen, amounting to a 10-0-0 rating of NPK.
I got a large bag of the granules for less than half price at a local nursery because the bag in question had mouse damage. (Speaking of which, I have only found evidence of mice on our property twice in almost five years, and once was when they broke into the corn gluten (again) and made one hell of a mess. Keep this stuff in a plastic or metal bin with a tight-fitting lid.) I sprinkle it liberally over a bed after I have done a really thorough weeding job and lightly rake it in. Water if you aren’t expecting rain in the next five days (i.e. you do not reside in the Pacific Northwest). There are two caveats: 1) Since this stuff suppresses germination don’t apply it anywhere that you want germination, such as an area where you have planted or will be planting within 6 weeks, and 2) You can’t expect perfection – there are some plants this stuff doesn’t effect, and if you left behind pieces of root they will still grow back (because they’ve already germinated). Overall, though, it is a definite work-saver. Most of the weeds do not return, so I have less work to do the next time I come through with my trowel and cultivator.
Another handy application of this product that Matt suggested is to mix it in with topdressings. Our compost bins do not get hot enough to kill most weed seeds, so when I topdress or mulch with our compost I get a lot more weeds than I suppress. Matt suggested that next time I am spreading compost, as long as it is not an area I will be planting (with seed) soon, that I mix the corn gluten with the compost or sprinkle it over the topdressed area and rake it in.
A great site for more information is the Iowa State University Department of Horticulture Corn Gluten Research Page.