Handy Homemade Weed Killers

Free or Cheap (And Safe) Herbicides

As summer kicks in, weeds go into overdrive. Tiny seedlings that required tweezer removal last time you looked are suddenly a yard high and wide. The formerly pristine driveway gravel is turning a lovely shade of green. The bird feeder has a jungle under it (some birds really are slobs). Pathways are vanishing, veggie beds are choking, and even the kids’ sandbox is infested with unwanted baby trees. What’s a mindful gardener to do?

For starters, put the tea pot on. Why? A tip of the teapot will kill off many weeds, especially small ones in paving cracks and crannies. Boiling water can penetrate to the roots of many weeds, and of course becomes totally harmless as it cools down. This works beautifully on soft tissue like leaves and basal rosettes, less well on sturdy blackberries or woody seedlings. It works weeding wonders on gravel driveways and in ornamental, stone-lined, dry stream beds. However, in cold weather, boiling water can cause brittle terra cotta or glazed pots to crack and may make soft, old bricks crack, chip, or flake apart, so this treatment is best reserved for warmer weather.

Leaves Of Grass

Grass is another great freebie weed controller. Really? Yup: Fresh grass clippings get hot enough to kill seeds and seedlings and can burn established plants if piled deeply, especially in hot weather. As clippings dry out, they cool down and make a fine mulch for the veggie bed (as long as the grass wasn’t treated with weed-and-feed or other toxins). Remember too that fresh grass clippings can overheat wetland plants, and can kill eggs and spawn of fish, frogs, and other aquatic life if dumped too close to streams or ponds.

Come autumn, leaves can transform weedy beds. A foot or more of autumn foliage, piled between ornamental plants, can smother weeds and prevent many weed seeds from germinating. To prep a new bed, sheet mulch generously with fallen leaves, heaping them as high as possible. Come spring, you can brush them aside to make planting holes, then add more leaves each autumn to keep the  weed-free groove going.  As a bonus, when the leaves break down, they’ll nourish your plants, help open tight soil, and assist in retaining soil moisture in hot summers to come. Huge leaves like bigleaf maple take a while to break down, so don’t heap them over young plants, but they are great for mulching the big guys at the back of a border or anywhere you need serious weed suppression.

Into The Woods

When establishing new gardens in less than ideal soil or hard to maintain places, I rely on wood chips. I’m not talking ground bark, but arborists’s chips, which involve the entire tree, including foliage, lichens, etc. They are also very useful weed killers: Deep wood chip mulches (12-18 inches) can kill off 80% of an established mat of ivy in about 3 months. Even shallower layers will help suppress this noxious weed, but the more you use, the better this technique works. Inexpensive hog fuel, which consists of various coarse grades of arborists’s wood chips, is an excellent tool for cleaning up weed-infested woodlands without harm to existing trees and shrubs, and any excess can be raked into walking paths once the weeds are gone.

I’ve been involved with designing, planting, and maintaining some really fun public spaces, including beds consisting of 5,000-10,000 square feet. These very prominent spaces are maintained by a handful of middle aged women working a few hours a month, and since the imported soil was weed infested, the first few years were a weeding nightmare. We finally got smart and applied thick wood chip carpets, topping them off annually where they wear thin, and now these extensive beds are far more manageable, if not utterly weed free (but what garden is?).

Natural, Non-Toxic Lawn Weed-&-Feed

One of the best herbicides for natural care lawns is corn gluten. This natural byproduct of corn meal manufacturing is Nature’s own weed-and-feed treatment. It prevents seeds from sprouting by drying out the tiny emerging plant. When a seed sheath cracks open, zap, the corn gluten dries the emergent seedling fatally out. To work this magic, the corn gluten must be thoroughly wetted down, since adding water releases an alelopathic substance that affects any kind of seeds (weed or otherwise). Wetting corn gluten also reduces losses to birds (crows and ducks love the stuff). You spread it with a whirly bird or drop seeder, coating the lawn (or bare garden soil) as evenly as possible. Flower and vegetable beds may need up to 30 pounds of corn gluten per 1,000 square feet. Well filled beds need less than emptier ones and row crops need heavier coverage than plants grown in dense patches or swales. Heavily watered gardens may need monthly treatment in summer.

Corn gluten is a tip-top fertilizer (9-1-0), making it as valuable in the vegetable patch or flower bed as on the lawn. It’s great for new lawns, but you don’t apply it until the seeds have sprouted, since…you get the picture. When the seed is well up, spread corn gluten thickly to keep the lawn weed free until it is well established. For established lawns, treat with corn gluten in fall (20 pounds/1,000 square feet), when the rains return and you’ll soon have lush, dense turf that crowds out dandelions (really). When you remove weeds in the lawn or anywhere, cover the bare patch with a handful of corn gluten and water it in well. Not only will new weeds be prevented, but the surrounding grass or plants will rebound with vigor.

Kitchen Killers

Plain old baking soda is the safest and most lastingly effective treatment for mossy roofs, sidewalks, decks and other hardscape areas. Sprinkle thickly over the moss and let it do its thing. When the moss turns rusty brown, rake it away and repeat the treatment to get at the roots, which can penetrate quite deeply into brick and concrete. Once a roof is clean, just spread baking soda in spring and fall to keep moss from colonizing again. On lawns, mossy patches may need several treatments, but if there is more moss than grass, quite different treatment is required (and that’s a tale for another time).

I hear lots of hype about vinegar these days, and some of it is true, but not much. Though cheap white household vinegar (5% acetic acid) can work on seedlings and infant weeds, especially in hot, dry weather, it works best under perfect conditions. Vinegar tends to be diluted to ineffectuality by rain and wet soil, but horticultural vinegar concentrates, with an acetic acid rating of 10% or higher, are generally more effective, They too are best at burning seedling foliage and can sometimes penetrate to the roots of younglings; if the treated weeds are going to die, they’ll usually do so within 24 hours. On larger, established weeds, even vinegar concentrates usually only kill top growth so must be reapplied repeatedly.  Onward!