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Use organic soil amendments

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No matter what type of soil you have—sand, silt, clay, or good garden loam—it can benefit from using organic soil amendments, which take the place of ecologically harmful chemical fertilizers.

How to use organic soil amendments

The primary soil amendments for organic gardens, lawns, and landscapes are compost, lime, green manures, animal manures, and organic fertilizers. Compost improves the structure and drainage of soil that contains too much sand or clay. Lime increases the alkalinity of acid soil. Even good loam needs to have nutrients replaced each year that are used up by growing plants. This can be accomplished with compost, manures, or organic fertilizers.

  • Test your soil to find out what it needs. A soil test can determine your soil’s mineral content and acidity. Test every two to three years. Many gardeners add nutrients they don’t need, wasting time, money, and environmental resources. Test your soil with a home test kit from a garden supply center or have it tested (often for free) by your local cooperative extension. Use soil samples from several locations in your yard or garden, as results may vary. Test in the fall if you’re taking your sample to the cooperative extension, and avoid the spring rush. This also lets you apply lime in the fall, if needed.
  • Raise pH levels if necessary. In cool, damp climates soil is likely to be acidic, since rain washes away the calcium. Adding lime, which is ground limestone (calcium carbonate), raises the pH of acid soil. Use dolomitic lime, which also contains magnesium. Apply about 6 pounds of lime for every 100 square yards if you have average loam. For sandy loam, use 4 pounds and for heavy clay use 8 pounds. Be careful not to add too much lime. Also, don’t add lime to a garden bed where you plan to plant tomatoes or potatoes the following spring. Wood ash from a woodstove or fireplace can be used in place of lime, but don’t use coal or charcoal. In addition, wood ash also adds potassium and some phosphorus, and usually has about a 0-1-3 N-P-K ratio.
  • Use compost to add nutrients and improve soil structure. Using compost is the best way to add beneficial minerals, nutrients, and organisms to your garden. Compost also increases water retention, improves soil structure, and prevents erosion. See Make your own compost for information about composting.
  • Plant green manures. Green manures are crops that are grown to be dug into the vegetable garden, adding nutrients directly to the soil. Green manures also function as cover crops, preventing soil erosion and nutrient loss due to run-off. Often green manures are sown in late summer or early fall and dug in the spring, before they flower and go to seed. Legumes, such as peas and beans can be grown as both crops and green manures. Peas and beans have the added benefit of “fixing” nitrogen: bacteria found in nodules on their roots take nitrogen from the air and convert it into a form that plants can absorb. After harvesting the peas or beans, just turn the plants under into the soil. Other green manures include winter rye and winter wheat. Sown in late summer, they’ll grow in early spring. Then you can till them into the soil before planting late spring crops. Mustard is another excellent green manure—it’s quick growing and keeps out weeds.
  • Apply animal manure. Well-rotted manure from organically-raised cows, horses, and chickens adds beneficial nutrients to garden soil. Don’t apply manure and lime at the same time, as it creates ammonia gas and wastes beneficial nitrogen. Note that it’s not necessary to add animal materials to your garden to maintain healthy soil. Recent E. coli outbreaks linked to commercially-produced vegetables have resulted in many organic gardeners avoiding use of animal manures altogether.
  • Use organic fertilizers. If you can’t make or buy enough compost, or your soil needs a lot of a specific nutrient, use an organic fertilizer, rather than resorting to chemical fertilizer. Organic fertilizers may be plant-based products such as seaweed meal, or animal-based products such as blood, fish, or bone meal.

Find it! Organic soil amendments

Using organic soil amendments helps you go green because…

  • They eliminate the need for synthetic chemical fertilizers, keeping chemicals out of the food we eat, the air we breathe, and the water we drink.
  • They help condition the soil so it retains water. Lawns, flower gardens, vegetable gardens, and landscapes therefore require less frequent watering.
  • They keep you from mowing your lawn as often, since organic lawn fertilizers release nutrients more slowly. This cuts down on the air and noise pollution caused by lawnmowers.
  • They help prevent soil erosion.

While humans have practiced agriculture for over 10,000 years, only in the last 50 years have people become heavily reliant on synthetic chemical fertilizers.[1] While this practice caused yields to increase and the price of food to drop, the use of synthetic fertilizers creates a false sense of cheaper food, because it doesn't include the external costs of cleaning up resulting pollution.[1]

In 1998, worldwide usage of synthetic chemical fertilizers was 137 million metric tons—about 20 million tons (or 15 percent) of which was used in the US.[1] Current agricultural practices account for 70 percent of pollution in the nation's rivers and streams.[1] Another long-term effect is that synthetic fertilizers gradually increase the acidity of the soil until it begins to impede plant growth.[1]
Runoff of agricultural chemicals—as well as silt, and animal waste—has polluted more than 173,000 miles of waterways.[1] After it rains or snows on land treated with synthetic fertilizer, the chemicals may leach into streams and rivers, or seep into the soil, entering the groundwater.[2] This agricultural runoff is the major cause of water pollution in the US and is a primary contributor to environmentally disastrous “dead zones” such as that in the Gulf of Mexico.[2]

Every homeowner with a lawn or garden impacts the health of local resources, and collectively, the actions of individual homeowners impact the health of the soil and water on our planet. Synthetic fertilizers, for example, kill beneficial microorganisms in the soil, which control insect pests and combat disease, while organic fertilizers feed the soil as well as the microorganisms the soil contains, resulting in fewer pests and disease problems over the long run.[3]
However, excessive fertilizer of any kind diminishes biodiversity due to the effects of nitrogen runoff on ecosystem balance.[1]


  • acidic: A pH of 1.0 to 7.0.
  • alkaline: A pH of 7.0 to 14.0.
  • compost: A mixture of decayed organic matter that is used for fertilizing and conditioning soil.
  • dolomitic limestone: Ground limestone (calcium carbonate) which also contains magnesium.
  • green manure: A crop grown to be dug into the soil, thus directly adding nutrients.
  • legume: Member of the Fabaceae or Leguminosae family of plants, including peas, beans, peanuts, lentils, chickpeas, and soybeans.
  • lime: Ground limestone (calcium carbonate).
  • loam: Well-balance soil containing equal amounts of sand, silt, and clay.
  • manure: Livestock excreta used to fertilize soil.
  • nitrogen fixing: Process by which bacteria that live in root nodules take nitrogen from the air and convert it to a form that plants can absorb.
  • N-P-K ratio: The percentage of the nutrients nitrogen (N), phosphorus (P), and potassium (K) by weight; for example, a fertilizer listed as 5-10-5 is 5 percent nitrogen, 10 percent phosphorus, and 5 percent potassium.
  • organic: Any material made up primarily of carbon.
  • pH: The measured acidity of soil.

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Worm Castings are an organic fertilizer too. You can make your own by raising worms or buy premade worm castings online.

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