Chemical Combinations in the Garden

By Frank Rauscher
Published: June 5, 2018 | Last updated: April 29, 2021 10:27:18
Key Takeaways

Combining chemicals in the garden is tricky business. Mix the right ones together, and you’ll be rewarded with a synergistic result. Mix incompatible chemicals together, however, and you’ll be in for a whole lot of trouble.

First off, what exactly is a chemical? A chemical is simply any substance consisting of matter. This includes liquids, solids, and gases. Chemicals can be a pure substance, an element, or a mixture of elements. They can occur naturally or be made artificially. In other words, just about everything you put your hands on includes chemicals.


That also means everything you use in your garden has chemicals. Since it’s easy for chemicals to come into contact with each other in the garden, it’s important to understand their compatibility. Some combinations are synergistic, and some are downright dangerous.

Household Chemicals

Hydrogen peroxide, bleach, vinegar, and other household chemicals sometimes make their way into the garden. Many of these are incompatible. For example, vinegar and hydrogen peroxide together create peracetic acid, which can harm you if sufficiently concentrated, while bleach and many acids release chlorine gases when mixed. Even carpet, which is a material made of many chemicals, can create toxins when saturated with another chemical. These incompatibilities can become an issue when making homemade grow room remedies. Just because a mixture is recommended on a website is no reason to assume it will be safe when you make it. Many of these formulas have not been sufficiently studied. A website presenting a home remedy should clearly point out the possible dangers or unintended consequences if the mixing is not done properly. The instructions should also make it clear the exact quantities to mix and at what temperature. Less than this would not be responsible. Of course, you can always opt to buy premixed products, which have been studied and mixed at safe levels for use.


Nutrient Chemicals

The nutrients you use in your garden are also chemicals, and they can be produced synthetically or naturally. Take nitrogen, for example. In its elemental form, it is an anion (has a negative charge). However, plants are unable to directly absorb nitrogen anions. The nitrogen must first be converted into nitrate anions or ammonium cations (which have positive charges). Nitrogen-fixing bacteria can do this naturally in the soil, while commercial fertilizer manufacturers have processes that synthetically perform this vital conversion. In the end, the same chemical is produced.

Regardless of how they were created, some of these chemicals are synergistic to each other in that the uptake of one will benefit the uptake of another. Take chlorides, for example. A chloride is an anion. It moves easily with water throughout grow media and does not absorb into soil particles. Research has found chloride ions increase the activity of cations (which have positive charges) in soil and nutrient solutions as well as increase the uptake of cations through the entire growth period. This means an adequate supply of chlorides, from sources such as potassium chloride, increases absorption of cations and boosts yield.

There are also antagonistic relationships between some nutrients. Studies on tomato growing demonstrated that an increase in nitrogen influenced a decrease in plant phosphorus uptake. In this same study, this increase of nitrogen created additional uptake of calcium, iron, and zinc. In contrast, when phosphorus was increased, plant uptake of iron and manganese improved, while nitrogen, potassium, calcium, and magnesium uptake decreased.


Synergism and antagonism cause interactions between plant nutrients. Negative ions are balanced by positive ions. An abundance of negative ions, however, acts antagonistically to the effect other ions have on plant nutrient uptake. Sometimes the soil solution reactions are complicated, and antagonism between ions becomes obvious.

A key lesson here is to follow application instructions. Overloading the soil or grow media with one nutrient could adversely affect the plant uptake of others. Also, always read the label before using a chemical. This is where the dangers of mixing, fumes, or application are presented.


Pesticide Chemicals

This category of chemicals includes fungicides, insecticides, biocides, and herbicides. These kill diseases, insects, and other pests. They can play a big role in helping growers keep crops healthy and productive, and they’re vital for saving a plant from decline and death.

When considering overall soil chemistry and the goal of creating and sustaining a living soil, however, the use of these same chemicals can be catastrophic. For example, an application of fungicide will not only kill the diseases hurting your crop; it will also destroy the beneficial mycorrhizae in your soil. Likewise, when glyphosate—an herbicide designed for foliage application—is inadvertently applied to the soil, soil microbes use it as a food source and break it down to a chemical known as aminomethylphosphonic acid (AMPA). While studies haven’t proved this acid to be detrimental to soil health, there are scholarly debates about the effects of glyphosate on the soil’s environment.

With any chemicals we use, careful application is extremely important and the importance of reading the label can’t be overstated enough. This will not only protect your plant, but it will also protect the environment and, most importantly, your health. For example, glyphosate is classified as a carcinogen for humans, so frequent exposure to it should be recognized as at least potentially dangerous. However, proper usage (a surfactant like a soap must be added to help the chemical stick to the foliage) can enhance the effectiveness of the product and prevent additional sprays.

Chemicals of all kinds are commonplace in the garden. It’s important to understand how to use them and their compatibilities to ensure the safety of your plants, the environment, and yourself. For additional information, on chemical incompatibilities and synergies, and to review the reference information for this article, scan the QR code.


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Written by Frank Rauscher | Writer, Owner of Garden Galaxy

Profile Picture of Frank Rauscher
During his many years of service in horticulture, product development and sales, Frank has performed innumerable visits to landscapes to facilitate a correction for struggling plants or assist with new design. He also writes for Southwest Trees and Turf and The Green Pages, is the owner of Garden Galaxy and manages several websites. He has four children and eight grandchildren.

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