Garden & Greenhouse


Plant Extracts and How They are Used

Posted May 14th, 2018 by Eric Hopper in ,

Some of the most impressive recent innovations in the horticultural industry have been in the area of plant extracts. It is kind of strange to realize that some of the greatest advancements in organic and natural plant care come from the plants themselves. Plant extracts are defined as a group of substances extracted from different parts of a plant. These substances contain compounds with specific beneficial properties. The compounds can be obtained from various parts of the plant, including the roots, bark, seeds, flowers, leaves and fruits. A plant extract can contain multiple compounds or be isolated into a single compound. Plant extracts are now commonly used in plant fertilizers, insecticides, fungicides, and growing media.

Vegan Fertilizers

Vegan nutrients are completely plant-based nutrients that supply plants with the essential elements needed for growth. Vegan fertilizers are usually made up of a combination of plant extracts and plant-based ingredients. The following are some of the most commonly used plant-based ingredients in vegan fertilizers.

Alfalfa Meal

Alfalfa meal is rich in trace elements, but it also has an abundance of natural growth stimulators. Vegan fertilizers containing alfalfa meal will accelerate growth rates and also promote abundant fruit or flowers.

Kelp Meal/Kelp Extract

Kelp meal is a source of readily available potassium and a variety of micronutrients and plant hormones. This great soil additive can also increase overall plant health and vigor. It is the plant hormones that can “boost” a plant’s growth. Kelp extracts are commonly used as a foliar treatment to deliver plant hormones in the most direct and efficient manner. Many indoor horticulturists and greenhouse growers use kelp to deliver powerful growth hormones during crucial transition stages, such as when the plants are moved from the cloning stage to the vegetative stage. Due to the high amount of growth stimulating hormones, kelp foliar applications should be avoided in the later stages of fruiting or flowering.

Compost From Plant Material

Compost is a general term referring to composted (aged and broken down) organic matter. Compost can be derived from a number of different sources, but is usually derived from plant material and/or manure. Although compost is not specifically a plant extract, it can still contain many beneficial properties of the plant material that is composted. Not only does compost have significant nutrient value, it also provides an abundance of microbial life to the soil mixture. The beneficial microorganisms derived from compost are the foundation for nutrient uptake.

Soybean Meal

Soybean meal is a plant-based byproduct of the soybean industry. This slow-releasing nitrogen source is a great fertilizer for plants that require adequate nitrogen for two to three months.

Camellia Meal

Camellia meal is a byproduct of the camellia seed oil industry. Camellia meal, also known as wild flax, is high in nitrogen and has good moisture holding capacity.

Neem Seed Meal

Similar to camellia meal, neem seed meal is also a byproduct of the seed oil industry. Neem seed meal has a good amount of nitrogen, phosphorus, potassium, and is an excellent source of macro- and micronutrients as well.

Cottonseed Meal

Cottonseed meal is a byproduct of the cotton industry. Cottonseed meal is a vegan slow-release fertilizer that is acidic in nature. Cottonseed meal is a common ingredient in fertilizers specifically developed for acid-loving plants. Cottonseed meal contains nitrogen, potassium, phosphorus, and other micronutrients.

Amino Acids (Derived from Plants)

Many indoor horticulturists are discovering the benefits of using amino acid supplements. Amino acids are the building blocks of the proteins and enzymes that influence plant vitality (more specifically plant metabolism) and contribute to a plant’s structural integrity. The largest benefits of supplementing an amino acid formula are increased nutrient uptake and overall stress reduction. Amino acid supplements come in many forms and are often combined with other beneficial ingredients. The plant protein hydrolysate is a good example of a plant extract product that is rich in amino acids. There are also amino acid powders derived from plant sources, such as soybeans. These amino acid fertilizers usually contain a good amount of soluble nitrogen and aid in chelating various micronutrients, including manganese, iron, zinc, and copper. The bonding of ions in the chelation process makes the absorption of key micronutrients more efficient.

Plant Extracts in Pesticides and Fungicides

Most plants have their own built-in mechanisms to protect themselves from various pathogens or animals. As scientists gain understanding about the specific compounds created by plants for defense, potential plant-based pesticides and fungicides are discovered. Particular compounds in plants, due to their natural antimicrobial and insecticidal properties, are now being incorporated into natural pesticides and fungicides. These plant extracts can be directly used or the specific substances responsible for the antimicrobial or insecticidal properties can be isolated and incorporated into pesticides and fungicides.

Aloe Vera Extract

A relatively new extract to exhibit potent anti-fungal properties is an extract obtained from aloe vera. Aloe vera extracts have been found to have anti-fungal activity against some of the most common post-harvest pathogens, including penicillium expansum (blue mold) and botrytis cinerea (bud rot). Aloe vera extract is also used as a soil amendment to control moisture. In fact, aloe vera added to a soil which has been inoculated with beneficial microorganisms will protect the microorganisms from extreme conditions. Prepackaged soils that do not contain aloe vera extract will not be able to protect the beneficial microbes when the soil is stored in hot or cold conditions.

Garlic Extract

Garlic extracts are becoming more and more popular in organic horticulture. This powerful plant has a natural fungicidal property and the ability to destroy bugs on contact. As an insecticide, garlic extracts work most effectively as a pest insect deterrent. Because pest insects are adversely affected by garlic, they will immediately pack up and find another place to live. Many pesticide companies are combining garlic extracts with other organic active ingredients to maximize effectiveness.

Clove Oil

Similar to garlic extracts, clove oil is becoming a popular additive in many organic pesticides and fungicides. Eugenol is a compound extracted from clove which has displayed powerful antimicrobial properties. Insecticidal products made with clove oil are excellent contact killers.

Rosemary Extracts

Special compounds found in rosemary extracts block the octopamine receptors of many pest insect varieties. Pest insects sprayed with a rosemary extract solution will experience paralysis and eventually death. Because octopamine receptors are specific to insects, rosemary-based insecticides show great promise as a safe alternative to chemical insecticides. With a rosemary-based insecticide, growers can safely get rid of pest insects without causing any harm to other living creatures.

Cinnamon Oil

Cinnamon oil is becoming more popular as an additive in organic insecticides and fungicides. As an insecticide, cinnamon oil extract works by disrupting a pest insect’s neurotransmitter. Because these neurotransmitters are specific to insects, it makes this type of insecticide extremely safe for people, pets and other vertebrates. The compound cinnamic aldehyde is a plant extract of cinnamon which has been revered for its antimicrobial properties. This isolated compound shows great potential as an organic fungicide.

Spearmint Extracts

Spearmint extracts have been shown to work as a deterrent to a variety of pest insects. Few plant species are sensitive to spearmint which makes spearmint-based insecticides great for small or sensitive plants. Spearmint extracts can be mixed into a solution and young plants or seedlings can be submerged for complete coverage.

Thyme Oil

Thyme oil is another common plant extract used in organic insecticides. Thyme oil has an insect deterrent property and has been shown to repel a wide variety of pest insect species.

As more is discovered about the properties of individual compounds found in plants, additional specific compounds that are beneficial to horticulturists will be isolated. Plant extracts are slated to be the most environmentally friendly option when it comes to pest insect and pathogen control. They also show great

promise as high quality fertilizers and soil amendments. There are literally hundreds of thousands of different plant species that have been discovered and identified. The large number of plant species and the fact that each species contains its own unique compounds illustrate how vast the world of plant extracts really is. Only time will tell which plant extracts will affect the future of horticulture. As exciting as that may be, there are already many plant extracts and plant-based products that provide a great many benefits to our gardens.

Eric Hopper resides in Michigan’s beautiful Upper Peninsula where he enjoys gardening and pursuing sustainability. He is a Garden & Greenhouse senior editor and can be contacted at

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