Organic Herbicides

Organic herbicides can be used in organic gardening and farming to weaken or kill unwanted plants, otherwise known as weeds.

Selective herbicides are used to manage weeds that are either growing in between rows of crops, or to kill moss and weeds in lawns. Non-selective herbicides are used in areas where no plants are wanted, such as a gravel path. They may also be used to destroy remains of plants after a crop has finished.

Most organic herbicides are non-selective, i.e. they destroy all plants, without leaving residues in the soil that would prevent another crop from being grown in the next season. Generally they will also not harm the worms, beneficial bacteria and fungi that are a vital part of the life of the soil. Many non-organic weed killers will harm these forms of life and therefore weaken the growing power of the land.

Although technically speaking an organic herbicide could be any weed killer that includes carbon, which is almost all of them, these days the term has come to mean herbicides that are approved for use on organic land. This can vary in different jurisdictions so if organic certification is important to you (for example if you are selling your produce as organic) you will need to check with the appropriate state agency.

Organic herbicides may be either natural substances, synthetic compounds or processes like burning and mulching.

Vinegar

Vinegar is often used as a weed killer. In concentrations of between 5% and 20% acetic acid it can be used to kill surface growth of plants. Most plants will not draw it down into the root, so they can regrow and will need to be treated again. Some plants need two or more treatments.

Vinegar or acetic acid is also used in most of the synthetic compound weedkillers. AllDown, Matran 2 and Xpress are examples of patent herbicides that contain acetic acid as one of the active ingredients.

Other Natural Weedkilling Agents

Other agents that are used in compound patent herbicides include clove oil, garlic, thyme oil, citric acid and plant extracts such as yucca.

Burning

Fire is a method of weed control that is used in some situations. The process of burning unwanted plants is something that has been done for centuries. It clears the land after harvest and has the advantage of producing ash which enriches the soil. It burns many of the seeds which can reduce weed growth in future years. It is also completely natural.

However, open burning on land is now illegal in many areas, because of the risk of fire spreading and/or because of the pollution caused by the smoke. Controlled burning is allowed in some countries with flame being applied to a small area at a time by tractor.

Infra-red heat treatment is another way of burning the finished crop which does not involve the dangers of flames. This is permitted in most areas.

Mulching

Mulching is the process of putting something over the ground to stop weeds from getting light and oxygen. This is an example of a selective organic herbicidal process.

All of the ground between the wanted plants is covered with plastic, canvas or other material and any weeds that sprout in the ground beneath it will not be able to grow. Putting straw between strawberry plants is a traditional example of mulching.

In a garden, and even in many organic farming environments, the most common form of weed management is simply to pull the weeds up by hand or with a hoe. This is the simplest way to control weeds. However, for larger areas of unwanted vegetation, organic herbicides can be useful.

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Peter Charalambos

Author: Peter Charalambos

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