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Organic Gardening

Organic Gardening

Interest in organic gardening—using organic and natural materials for fertilization and disease and insect control—is increasing.

Much of the interest is on reducing or eliminating use of man-made pesticides for controlling insects and diseases. There is less interest in the use of natural and organic fertilizers.

Organic gardening in Mississippi faces some serious problems with the rapid loss of soil organic matter and severe insect and disease pressures on vegetable plants. Organic gardeners, to ensure the greatest chances for success, should have the garden soil tested for pH and nematodes.

The most beneficial input for both organic and conventional gardeners is to add organic matter to the soil. This can be done by adding composted or fresh organic materials and incorporating them into the soil. Gardeners need to pay attention to the amount of nitrogen in the materials they are adding. Straw; fallen, dried leaves; sawdust; wood chips; and paper should be blended with a high nitrogen material like grass clippings, manure, or blood meal since incorporating large amounts can actually keep the nitrogen in the soil from the crop plants while decomposing. The nitrogen becomes available again after decomposition is through.

Soils with a low pH (acid) can be corrected using limestone, ground oyster shells, wood ashes, or dolomitic limestone. Adding organic matter benefits soils with a high pH (alkaline).

Animal manures are the most widely used organic fertilizers. Unfortunately, their composition varies with the source, age, degree of rotting, water content, and amount and kind of litter used.

Green manures and cover crops can also be used to provide nutrients. When allowed to grow over the winter, hairy vetch or crimson clover can fix up to 100 pounds of nitrogen per acre. Southern peas can be grown during summer to provide nitrogen for fall vegetables. Green manure crops should be mown and plowed into the soil at least four weeks prior to planting the next crop.

Most organic materials do not contain plant nutrients in balance with plant requirements and must be supplemented to correct these imbalances. A well-leached animal manure has an estimated fertilizer value of 1-1-1, or 20 pounds each of N, P2O5, and K2O per ton of manure. Besides being relatively low in nutrient content, the nutrients are available more slowly than nutrients from inorganic sources. This protects nutrients from leaching, but when a rapid change in nutrient level is needed, this can be a problem.

Controlling diseases and insects by natural means alone is difficult. There are several insecticides available including Bt formulations for caterpillar control and spinosad or pyrethrums for other insects, but disease control is difficult. Neem oil, bicarbonate, and copper- and sulfur-based fungicides provide some protection against diseases, but the best results for disease management come from selecting resistant varieties and proper timing and spacing during planting. For these reasons, organic gardening is easier on a small scale.

Nutrient Content of Organic Materials

 

Percent Nutrient

  N P2O2 K2O Availability
Rock Phosphate 0 20 to 30 0 very slow
Bone Meal 1 15 0 slow medium
Compost up to 3 1 1 slow
Dried Blood 12 1.5 .5 medium rapid
Fish Emulsion 5 2 2 rapid
Cotton Seed Meal 6 3 1.5 slow medium
Cow Manure, fresh .25 .15 .25 medium
Sawdust 4 2 4 very slow
Wood Ashes 0 1 to 2 3 to 7 rapid

To increase chances for success, organic gardeners should follow these practices:

  • Plant disease- and nematode-resistant varieties.
  • Use marigolds, mustard, solarization, and organic products like Clandosan 618 to control plant parasitic nematodes (see Extension Publication 483 Nematode Control in the Home Garden).
  • Plant seeds from disease-free plants.
  • Plant only healthy vegetable transplants.
  • Place a cardboard collar around plant stems at ground level to prevent cutworm damage.
  • Incorporate plant residues and animal manures early to allow sufficient time for them to decompose before planting.
  • Use mulches to control weeds and keep soil from splashing onto the plants and fruit.
  • Use aluminum foil or reflective plastic mulches to repel aphids and thrips that injure plants and also transmit plant viruses.
  • Plant as early in the spring as possible to avoid some insect problems.
  • Keep the garden free of weeds that may harbor diseases and insects.
  • Hand-pick insects.
  • Water so plants are not wet at nightfall.
  • Remove diseased plants and plant parts from the garden.
  • Control insects using biological controls and natural products.
  • Rotate garden areas.
  • Encourage natural insect predators. Trap slugs under boards and moist burlap laid on the ground, or use beer traps.
  • Stay out of the garden when the plants are wet to prevent spreading diseases.
  • Do not use tobacco products while working in the garden.
  • Mix different vegetables in a row to eliminate monocultures and the chance for a disease to spread rapidly.
Drawings with beneficial insects listed: lady beetle, assassin bug, tiger beetle, praying mantis, minute pirate bug, and green lacewing.
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