Wise Owl
A Homeowner's Guide to Organic Lawn Care
Organic Lawn Care

ORGANIC LAWN CARE
Why Organic?
High Cost of Synthetic Pesticides
  Effect on Humans and Pets
  Environmental Concerns
  How They Damage Your Lawn
Organic Overview
  Healthy Soil
  Appropriate Plantings
  Thick, Deep-Rooted Grass
  Regular Maintenance
Lowdown on Lawn History
  The New World: Golf & Games
  Parks and Suburbs
  Communism and Crabgrass
Know Your Lawn
  Soil
  Water
  Grass
Lawn Rehab (Planning)
  Starting Off Right
  The Future (What You Want)
  The Present (What You've Got)
Lawn Rehab (Practice)
  Thatch
  Weeds
  Compaction
  Soil Amendments
  Overseeding
  Fertilizing
Regular Maintenance
  Mowing
  Watering
  Weeding
Seasonal Maintenance
  Whacking Weeds
  Aerate the Soil
  Trashing Thatch
  Amend the Soil
  Keep It Green: Fertilize
Pets, Pests & Problems
  Dogs and the Perfect Lawn
  Pest Control: Guidelines
  Bugs & Thugs
  Moles
  Weed Control
  Diseases
Alternatives to Grass
  Ornamental Grasses
  Shade Lovers
  Sun Lovers
  Low Water Ground Covers
  Under Pines -- Acid-Tolerant
Starting a Lawn
  Grass Types & Methods
  Preparing the Site
  Preparing the Soil
  Planting
  Caring for New Lawns
Switching from NitroLawn
  To Do List: Any Time of Year
  To Do List: Fall/Early Spring
  Using a Lawn Care Company
Sites & Sources
  Books & Articles
  Websites



Garden Supply
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Organic Weed ControlVinegar-Based and Citrus-Based Weed Killers
Learn how they work, and how to use them effectively.
by Ann Lovejoy, Fine Gardening Magazine

A few years ago, several people told me they were able to control their weeds by spraying them with inexpensive kitchen vinegar. I decided to try it and wound up wasting several gallons without seeing the slightest effect on the weeds in my driveway. This prompted me to do some research, and I discovered some data from the USDA which showed that regular kitchen vinegar containing 5 percent acetic acid won't control weeds, but vinegar concentrates of 20 percent acetic acid are, in fact, very effective herbicides.

Vinegar concentrates are applied in two ways: They are either sprayed directly on the plant (as a contact herbicide) or they are applied to the soil (as a soil drench). Spraying the product directly on plants strips off the waxy, protective coating on the foliage, making the plants vulnerable to desiccation. Typically, the plant will dry out all the way to the root.

Vinegar concentrates that are sprayed onto the soil, on the other hand, work by lowering the soil pH to a level where the plants can't survive. This acidifying effect lasts from several months to a year, depending on the soil type and the weather. Once the soil pH is lowered, taproots will eventually starve, but before dying they will often have one last flush of growth from nutrients stored in the roots. Once the weeds are dead, which may take up to six months for some woody weeds, the soil pH will need to be brought back to a neutral level. To do this, add some lime at the rate of 5 pounds per 100 square feet and add a 3- to 4-inch blanket of compost to restore microorganisms. Some soil organisms will have been killed by the application of vinegar to the soil, but as long as the treated area is small, these critters will repopulate quickly from the surrounding unharmed soil when the pH is restored.

Vinegar weed-control products work best on warm, dry days when the temperature is above 65°F. Don't use the spray directly on plants just before watering or before a rain, because it will be washed off. In this case, not only will the vinegar not kill the plant, but it may act as a fertilizer, releasing nitrogen, among other things, into the soil.

Citrus-based weed control

Several weed control products with concentrates of lemon and orange oils are also available to home gardeners. I have used four or five of these products and found them to be effective and fast-acting. Like the vinegar-based products, they are most effective when used on dry soil on hot days. Some products combine both citrus oils and vinegar concentrates or include other ingredients, like clove oil. These products are all foliar sprays that kill most broad-leaved weeds on contact. Large, established, tap-rooted weeds like dandelions may need several applications of the citrus oil/vinegar blend to kill them.

Clearly, because of their high concentration and their effects on the soil, these products have significant limitations. Any products that change the soil pH are not safe for use on septic fields, near streams or ponds, on edible crops, or anywhere they may affect the roots of established trees or shrubs (which generally extend past the plant's drip line). Also, vinegar concentrates are nonselective herbicides, meaning they will destroy anything they come in contact with, including wanted plants and soil organisms. So use caution when spraying near garden plants.

Despite these limitations, vinegar products, especially the sprays, are extremely useful for spot-killing difficult weeds, including invasive ones, in a garden bed. They are also terrific for clearing up weeds in paving cracks, such as between bricks or stones and on gravel driveways. They don't leave any residue on concrete or stone but may leave a temporary stain on bricks. In addition, vinegar products are safer for the environment than traditional weed-control chemicals because they affect only the soil they come in contact with and don't leach into the groundwater. Furthermore, their effect is completely reversible at any time by amending the soil.

Even botanically derived herbicides like vinegar- and citrus-based products need to be used with caution, however. Like any herbicide or pesticide, they can be harmful to people, beneficial insects, nontarget plants, and wildlife that may be accidentally exposed to direct spray. Because of the high level of concentration of the vinegar in these products, it is a good idea to wear eye protection and gloves, and to avoid exposing the skin to the spray. Be sure to wash your hands well when you are finished applying one of these sprays.
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