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Organic Weed Control

Spring Cover Crop Summer Cover Crop Fall Cover Crop Inter-cropping Critical Period of Interference Cultivation Animals Minor Weed Control Principles
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Spring Cover Crop:

In the spring, plant as early as possible before weeds start to grow to prevent weeds from ever getting started. Use genetics that are bred for cold weather. If you cannot plant your actual crop early, plant a thick cover crop early. Astoundingly extremely early cover crops are flax, turnip, and peas. Flax and peas can be mowed before no-till direct seeding once you are ready to plant your actual crop.

USDA - Cover Crops
SARE Managing Cover Crops Profitably
Bern University Switzerland - biomass ranking
NRCS - Cover crops and termination method
Cornell - cover crops for vegetables
eOrganic - large scale mulching in very cold climates
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Summer Cover Crop:

After crops have been harvested in late spring or early summer, grow a summer cover crop for mulch roll down before the fall crop is planted. Great care must be used in selecting cover crops for the summer, since not all cover crops are easily terminated in the early fall.

North Carolina State - killing summer cover crops
North Carolina State - mechanically killing cover crops
Rodale - mow vs roll
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Fall Cover Crop:

In the fall, after harvesting a summer crop, grow a cover crop for later mulching in place the next spring. In warm climates, you can wait for the fall cover crop to mature next spring before direct seeding your actual crop. In cold climates, you may need to transplant instead of direct seeding.


eOrganic - winter killed cover crops
Cornell - cover crop trials
Bradford Research - cover crop trials
USDA NRCS - 4 way mixes perform best at least cost
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Inter-cropping:

After your actual crop has come up and the mulch is starting to deteriorate, plant a living mulch between the rows before weeds get a chance to grow. If possible, push the remaining mulch against the crop. Avoid even shallow cultivation as it also severely disrupts the mycorrhizal network. Plant the living mulch some distance away from your actual crop.

Most inter-cropping field trials have had very mixed success and even more so for no-till. Mainly because even legumes will compete for nitrogen until it is used up before they fix new nitrogen.

Helen Atthowe - living mulch examples
Gabe Brown - decrease herbicide use by increasing cover diversity
Veganic Permaculture
SARE - inter-cropping trials
Montana State - inter-cropping trials
Clover with broccoli
SARE - Crimson Clover
SARE - berseem
Missouri State - berseem clover
Archive Univ Cal Berkeley - berseem clover
Intercrop study with corn
Alfalfa in wheat
Organic Ag Center - numerous studies
College of Tropical Agriculture - Broccoli with clover
Crop Science - wait to intercrop
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Critical Period of Interference:

The only time that weeds critically affect yield for most crops is within the first few weeks after planting (Critical Period of Interference).

University of Florida
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Cultivation:

You may still need to shallow till occasionally. But if you have a good crop rotation, then you can time it for when you need to harvest root crops and disturb the soil anyway.

Weed em and Reap
ATTRA weed management
Manitoba Gov. - weed management in organic crop systems
SARE - Steel in the Field
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Animals:

During the growing season, use Chinese weeder geese to control grass weeds. Portable fencing may be necessary to keep them out of the grain crops. In the fall, after harvest, turn animals out on the stubble to suppress weeds and speed crop residue decomposition. Hogs can be used to dig up roots. Allow animals to graze between orchard rows. Mob grazing and diversity work the best to control weeds in pastures. The use of animals may require some extra measures to prevent contamination such as never using antibiotics on your animals, dung beetles, poultry and hogs to disrupt manure, fly parasites, never harvesting off the orchard floor, etc.

According to the CDC, EColi is essential for human digestion and most EColi are beneficial. Our focus should be to stop the excessive use of antibiotics, not the removal of animals from agriculture.

CDC - most EColi are harmless
EFAO News
University of Idaho
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Minor Weed Control Principles:

Weed seeds die more quickly with n-till


USDA NRCS - weed seeds die quicker with no-till

Roll cover crops at an angle different from the original row planting. Always seed in the same direction as the cover has been rolled. Get a seeder that can handle a thick mulch.

Plant row crops dense enough to quickly form a canopy, but not so thick that it reduces yield. This will allow the crop to outcompete weeds.

Plant early maturing and cold tolerant varieties. This will allow an early planting and reduce the window for the critical period of interference. It will also allow more time to plant a follwing cover crop. These varieties may have slightly reduced nutrients and yield, but in the long run, it will be worth it.

Pile wood chips for several months and spray with honey/sugar water to allow at least some partial decomposition before using them as mulch. Layer with air circulation pipes across the pile. Never use fresh wood chips directly on the soil as mulch since they will rob nitrogen from the garden as they start decomposing.

Most weeds need to be cut only after fully blooming and before seeding to kill them by cutting. If they are cut before fully blooming, they will only keep trying to bloom.

Not all weeds are bad. For example, some weeds can be allowed to grow along side brassica to support mycorrhizal fungus for the next crop.


Joseph A. Cocannouer
Oregon Biodynamic Group

Some plants and materials are allelopathic and can be used to advantage: barley, rye, wheat, oats, brassica, sunflower, sweet potato, tobacco, walnut shells, and sunflower shells.

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