Extension Educator, Horticulture
I came across some really amazing and somewhat depressing numbers the other day. Just one lambsquarter plant can produce 72,450 seeds in one growing season. Or one redroot pigweed can produce 117,400 seeds in one year. If we all ate lambsquarter or were awe struck at its beauty, this information would be good news. However for most of us weeds such as these compete with our garden plants for light, nutrients and water. With the healthy look of weeds during this dry hot weather maybe we should be shifting our culinary preferences.
Weeds have a few things in common. They go through their life cycle rapidly, flower quickly, produce vast quantities of seeds and have some seed adaptation for travel by wind, water or animals. By now weeds may be waist high and ready to take over.
As Roger Swain says "there are no pacifist gardeners." Once you decide to grow anything, whether its for food or beauty, you will at one time or another find yourself in literally hand-to-hand combat with weeds.
The battleground is bare soil. Dig a new garden bed and all those dormant weed seeds shoot up. Seeds may stay dormant for decades waiting to be brought to the surface where they can germinate.
Once you have decided a plant is a weed, here are some weed control options.
First identify the weed. Knowing their life cycles is the key to control. Annuals live one growing season and must come back each year from seed such as crabgrass, foxtail, lambsquarter and buttonweed. Biennials live two years producing the seed in the second year such as burdock and poison hemlock. With perennials the same plant comes back each year and they produce seed such as dandelions, creeping Charlie, and quackgrass.
The Midwestern Weed Identification and Control website has some great lawn weed pictures.
Whatever you do, do not let weeds go to seed. Be relentless. Weed too big to pull? Then cut or mow off the tops. Remember, "One year of seeding equals seven years of weeding."
Hoe, till or hand pull – This method must be continued throughout the season. Hoe and till shallowly so as not to damage the roots of desirable plants and bring more weed seeds to the surface. Perennial weeds will require frequent cutting until the food reserves are depleted.
Mulch - Mulching controls weeds by preventing light from reaching the seeds or seedlings. This method is best for controlling annual weeds. Organic mulches include wood chips, straw, dry grass clippings and even newspapers. Synthetic mulches such as black polyethylene may be used in vegetable gardens. However they must be removed every fall and last just a couple of years.
Plant something such as cover crops, ground covers or grass - Bare areas invite weeds. Scalp the lawn and weeds will germinate before the lawn mower sees the garage. In the garden plant buckwheat now to help deplete the weed seed bank. Winter rye can keep weeds from taking over bare soil areas and when tilled in the spring will enrich the soil.
Herbicides – The most common in home gardens is trifluralin sold as Treflan or Preen. It is a preemergent herbicide that means it keeps the seed from emerging through the soil. Therefore they do not control existing weeds. Also these herbicides work best against annual grasses.
Perennial weeds can be controlled by nonselective herbicides such as glyphosate sold as Roundup or Kleenup. It must be applied to actively growing plants to be effective. The area may be replanted as soon as the weeds are dead. Because glyphosate is non-selective, do not apply it or let it drift onto desirable plants. When using herbicides, be sure to read and follow all label directions and pay attention to the appropriate crops and the weeds they control.