We are dealing with another fairly wet summer this year, and weeds have been growing prolifically. It seems you turn your back and the weeding you did ten days ago was for naught. There are some really good reasons, however, why you should not give up the battle!
Weeds compete with our vegetables for space, light, water, nutrients and even air. Not only do weeds reduce plant health and vigor, but by crowding our vegetable plants and limiting air movement they encourage airborne diseases to proliferate. Weeds also harbor insect pests and provide beneficial conditions for diseases to perpetuate in the soil, sometimes for many years. (This is why crop rotation is so crucial.) Garlic mustard is an example of a weed that is allelopathic, that is, it secretes a chemical from its roots that actually inhibits roots of other plants. So regular weeding produces healthier gardens in the long run.
A simple strategy to reduce weed stress is to not allow weeds to go to seed, which can undo your efforts for literally years. Each seed head is another hundreds or thousands of weed seeds “planted” in your garden. Another is the no-till method where you don’t disturb the soil. Tilling inadvertently brings weed seeds to the surface, where they can germinate in the light. Most seeds are in the top six inches of soil, but are likely to germinate only in the top two inches.
With many perennial weeds (creeping Charlie, quack grass, burdock, Canada thistle, etc.) the problem is that during the effort of removal, roots easily break off and remain to regenerate once again, and in even greater numbers. Instead of attempting to pull up the entire plant and its roots, try this method for flowering weeds with brittle roots like Canada thistle: Cut off weed plants at their base once they have formed flower buds, and over time you will eventually deplete the plant’s energy reserves and kill them. In the meantime, put the flower heads in the trash (do not compost) because they can still mature after being cut off.
Burdock and horseradish, considered a weed by some, grow long taproots that are difficult to dig up. However, if you dig deeply you may be successful in eliminating them.
Weeds like Canada thistle don’t like competition, so sow a cover crop to smother them (you may need to do this several times). A thickly sown cover crop can often outcompete unwanted plants. Buckwheat has been recommended for this purpose, although it may take successive plantings and up to a year. Sow at 3-5 ounces per 100 square feet.
The sad story is that creeping Charlie and quack grass’s root systems must be dug up entirely to eliminate them. It’s best to start in early spring and work at it relentlessly even if only for a short time per day. Hand weed if that’s your preference and especially if the soil is still moist after a rain. Your best tools may be a sharp hoe (which cuts the weeds just below the soil surface), a dandelion digger (for long roots), and a garden fork for loosening the soil when working in a thick patch of weeds. Even if using a hoe or garden fork, the goal is not to actually disturb the soil and in doing so bring up more weed seeds. Hoeing kills most annual weeds, but not perennial ones. You may wish to plant a dense cover crop immediately after weeding a patch if you have time before planting your next crop to keep the weeds from coming back immediately.
One of the most effective and easiest strategies to fight weed infestation is to use mulch around (but not touching) your plants. Weed before applying it. Mulch serves multiple purposes in the garden: it not only keeps weeds down, but it helps prevent moisture loss, keeps the soil cooler and eventually provides nutrients to plants when it decomposes. Maintaining an evenly moist and cool soil bed for your plants mitigates plant stress from heat waves. Straw is an excellent mulch as it maintains its loft and thus insulating capacity, its light color reflects light away and it lasts the whole season.
A completely different type of mulch, made of black plastic, can be an effective tool also if spread tightly over the ground and well-anchored. Transplants are planted in X cuts in the plastic. It should be removed in the fall to allow the soil to breathe, however. This type of mulch does not keep the soil cooler but actually warms it, and does not improve the soil through decomposition. Newspapers in thick layers and corrugated cardboard can be used similarly to smother weeds.