Recently I came across a bag of old, badly stored flour in the back of a cabinet, sprinkled it over a renovated vegetable bed, and posted a picture on Facebook. A tidal wave of questions, stories and jokes followed, for several reasons. Many people have leftover flour from their pandemic baking days they no longer find appetizing, and free garden fertilizer is always the best kind. But before using flour in the garden, it’s important to have a plan that makes sense.
You can use old flour as fertilizer, to bulk up your compost, or to mark off the edges of a new bed. Or you can do like Jan Z did: “I wrote in flour BIG 40 on my neighbor’s lawn for their birthday, and it made the grass grow 10 times faster and so much greener. It lasted pretty much all summer.”
Using Flour to Enrich Soil
All flours contain nitrogen, the most important growth nutrient for plants, along with a long list of micronutrients including calcium and magnesium. The chart above shows the nitrogen content of five cooking flours you might find forgotten on a shelf. Chickpea (gram) flour leads the pack, but popular whole wheat flour is a definite player at 2.5 percent nitrogen. Nitrogen content aside, all flours feed soil microbes with active organic matter.
To use old flour as a fertilizer, it’s important to use only a little at a time, as in a moderate dusting, and to mix it in well. Then water thoroughly and keep the soil moist for a week before replanting the space. Expect to see a few light fungal patches here and there for the first few days. Because of the small size of flour particles, soil microbes can immediately make use of them. Research from the University of Arkansas suggests that the proteins in flour are completely degraded within 30 days under normal soil conditions.
Using flour in the garden may come with a small chance that germination and growth might be inhibited by the gluten in the flour, but I have not found this to be the case. I planted 5 different fall vegetables in soil amended with flour after a one week wait – spinach, radish, beets, bok choy and spinach mustard, and they all came up like little soldiers along with plenty of little weeds.
My fear of compromised germination was based on a false belief that corn gluten is a potent germination inhibitor because it is sold for that use in lawns. The initial research suggested a herbicidal effect from corn gluten, but now it is thought that corn gluten benefits turf mostly by feeding it. In my experience, using flour in the garden enriches soil but does not inhibit the emergence of veggies or weeds.
Using Flour in Compost
You can add old flour to your compost by sprinkling it between layers of coarse organic matter. The little particles disappear quickly when scattered into the crevices of decaying plants, and do not give off odors that attract pests.
The US Centers for Disease Control says to Say No to Raw Dough because uncooked flour may contain salmonella, E. coli, and other bacteria that can make you very sick. The heat of cooking kills these and other pathogens, but don’t worry that putting flour in your compost introduces these microbes, because they are already there. All the little animals that pass through the garden, be they birds, mice or rabbits, spread small amounts of bacteria you don’t want on your food. This is why we compost funky things, wash our garden produce, and don’t eat dirt.
Use Flour to Mark Off Lines
When laying out a new bed, walkway, or other landscape feature, use a line of flour or corn meal to mark off the edges. Stakes and string become a tripping hazard, while flour creates dark green lines in grass that often persist through a season. Story in point as related by Hunaybun H: “I grew up in a small, poor town. Our baseball team would make our lines on the field with flour instead of chalk because it was cheaper. We never had to wonder where to make the lines, we just followed the green, green line.”
Ready for the jokes about using flour in the garden? Bill P was the first to point out that adding a bit of yeast would make a raised bed, while others said why bother? Just use self-rising flour. Corrie J asked if the veggies came coated with flour, ready to fry straight out of the garden? Geneveive G said to enrich a bed with flour and plant flowers and have a flour flower bed. Meanwhile, Caleb G poured some old cake mix into his compost pile, and Anne E noted that “Someone left his cake out in the rain, and we’ll never have that recipe again.” Never let it be said that gardeners don’t have a sense of humor.