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Can fertilizer cause pest insect infestations on your plants?

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Is there a connection between the fertilizers you use and the pest insect problems you’re having? Decades of research says “yes.” In this article, you’ll find out what you can do about it!


If you want to seriously geek out on where synthetic nitrogen fertilizer comes from and what its impacts are, we suggest you read our article 5 facts you should know about synthetic nitrogen fertilizer.

In this article, we’re going to briefly discuss a side-effect of using synthetic nitrogen fertilizer that you probably don’t know about. We’ll also recommend a different, better soil fertility approach for you to consider.

Can fertilizer cause pest insect infestations on your plants?

If you’re not familiar with how soil microorganisms and plants interact, the notion that fertilizer could cause pest insect infestations might seem very strange. What mechanism(s) would explain the causality?

Let’s take a quick look at what the research says on this matter:

From the USDA’s SARE (Sustainable Agriculture Research & Education program):

“A review of 50 years of research identified 135 studies showing more plant damage and/or greater numbers of leaf-chewing insects or mites in nitrogen-fertilized crops, while fewer than 50 studies reported less pest damage. Researchers have demonstrated that high nitrogen levels in plant tissue can decrease resistance and increase susceptibility to pest attacks. Although more research is needed to clarify the relationships between crop nutrition and pests, most studies assessing the response of aphids and mites to nitrogen fertilizer have documented dramatic expansion in pest numbers with increases in fertilizer rates.”

How does feeding your plants synthetic nitrogen fertilizer cause them to attract pest insects?

“Cultural methods such as crop fertilization can affect susceptibility of plants to insect pests by altering plant tissue nutrient levels. Research shows that the ability of a crop plant to resist or tolerate insect pests and diseases is tied to optimal physical, chemical and mainly biological properties of soils. Soils with high organic matter and active soil biology generally exhibit good soil fertility. Crops grown in such soils generally exhibit lower abundance of several insect herbivores, reductions that may be attributed to a lower nitrogen content in organically farmed crops. On the other hand, farming practices, such as excessive use of inorganic fertilizers, can cause nutrient imbalances and lower pest resistance. More studies comparing pest populations on plants treated with synthetic versus organic fertilizers are needed. Understanding the underlying effects of why organic fertilization appears to improve plant health may lead us to new and better integrated pest management and integrated soil fertility management designs.”

-Altieri & Nicholls, “Soil fertility management and insect pests: harmonizing soil and plant health in agroecosystems.” Elsevier’s Soil & Tillage Research Journal

In short, if you want to increase the likelihood of pest insect infestations on your plants, over-fertilize them and/or feed them synthetic nitrogen fertilizer. Then, you can spend time, money, and effort applying pesticides to try to get rid of the problem.

Biological soil fertility

However, if you want to grow healthy garden plants with strong immune systems and robust communities of symbiont microorganisms, we suggest you take a more holistic approach: creating biological soil fertility.

Biological fertility puts an emphasis on regenerating microbial life in the soil so as to:

  1. help symbiont microbes bring the exact nutrients a plant needs to the plant when it needs them; and
  2. reduce nutrients leaving the soil system in the form of pollution. 

With biological soil fertility, your plants won’t be a magnet for pest insects and will be better equipped to fend off whatever pest insects they might encounter (especially if aided by predatory insects in your garden/farm system).

A predatory lacewing larva gobbles up an aphid (a pest insect) in our garden. No human intervention required.
A predatory lacewing larva gobbles up an aphid (a pest insect) on our edible rose plants. No human intervention required.

5 ways to build biological soil fertility in your garden or farm

There’s no one-size fits all model that will work exactly the same way for every garden or farm on earth. Each of us has a different climate, different soil types, different plants, different resources available, etc.. A rural farm in south Texas is going to be quite different than an organic garden in Portland, Maine.

However, below are 5 methods that are universally applicable for building biological soil fertility. The more of these you can check off your list, the healthier your growing system is likely to be:

1. Avoid tilling your soil.

Use no-till methods which minimize or eliminate soil disruption, leaving your microbial communities undisturbed. No-till also supports native pollinators which overwinter and lay eggs in your soil (example: 70% of bee species are ground-dwelling), many of which are now extinct or critically endangered.

Also, leave your crop debris to decompose on the soil surface, helping to feed the beneficial fungi, bacteria, and other soil microorganisms in your soil system, while increasing soil organic matter/carbon.

Winter peas sprouting in one of our no-till garden beds. We simply pul the mulch and decomposing plant debris aside, and sow our seeds. These peas offer delicious greens and pea pods, while serving as a cover crop as well.
Winter peas sprouting in one of our no-till garden beds. We simply pull the mulch and decomposing plant debris aside, sow our seeds, and cover them with a light layer of compost. These peas offer delicious greens and pea pods, while serving as a cover crop as well.

2. Use microbe-dense worm castings or “hot” compost instead of synthetic or mineral fertilizers.

Not surprisingly, the quickest way to increase biological soil fertility is to add biology to your soil. Top-dressing your soil with worm castings and/or finished hot compost is the best way we know of to drastically boost biological soil fertility. Hot compost does not mean that the material is hot, it means it was made using the Berkeley hot compost method or similar methods. 

Yes, there is nutrition in these materials, but their near-magical effects on plants are primarily due to the huge loads of beneficial microbes present. If you’re starting garden beds from scratch, you can also consider methods such as hugelkultur which can provide decades of biological soil fertility.

If you have a large growing area and not a whole lot of worm castings or compost, make actively aerated compost tea (AACT) and apply it as a soil drench and/or foliar spray several times a year (or more if you have poor soil or your plants are showing signs of foliar diseases).

See the worms in these seedling transplants? As you might be able to tell from this photo, worms help aerate the soil, disperse nutrients, and increase the quantity and distribution of beneficial soil microbes. Worm castings make one seriously amazing soil amendment.
See the worms in these seedling transplants? As you might be able to tell from this photo, worms help aerate the soil, disperse nutrients, and increase the quantity and distribution of beneficial soil microbes. Worm castings make one seriously amazing soil amendment.

*Note: We top-dress 2″ of castings/compost on new beds and/or when our mulch has been broken down to soil, but we use an AACT soil drench whenever we want to add biological fertility to a bed that still has a thick layer of mulch on it. You can buy high quality worm castings at a great price via Unco.   

3. Avoid pesticides.

Measuring the impacts of various pesticides (insecticides, herbicides, fungicides, etc) on soil microbial communities in every type of soil and planting system is nigh impossible, especially when you start combining and applying different types of pesticides throughout the year.

Our general philosophy (based on the Precautionary Principle) is that it’s a good idea for humans to avoid ingesting endocrine disrupting and neurotoxic pesticides, especially if you’re a pregnant mother, an infant, or a child. (The American Academy of Pediatrics happens to agree with our position.)

We think the same philosophy holds true for applying these substances to your soil microbial communities as well. If you have to use a pesticide, make sure it’s OMRI listed.

Many pesticides used in organic gardens and farms (all of which are OMRI listed) are completely harmless and are actually just strains of beneficial bacteria that you can spray on your plants – they’ll outcompete or consume the pathogenic microbes. OMRI listed organic pesticides that we use and recommend are available in our organic gardening supplies store

An American lady butterfly (Vanessa virginiensis) foraging garlic chive flowers. Pesticides take an enormous toll on beneficial insects (pollinators and predators).
An American lady butterfly (Vanessa virginiensis) foraging garlic chive flowers. Pesticides take an enormous toll on beneficial insects (pollinators and predators).

4. Always cover your soil.

Do you have a garden? Always keep your soil covered.

Wood chips, mulch, or chopped leaves all work great, in addition to trying to keep living roots in the soil throughout the year (plant roots feed microbes and microbes feed roots). If you’re a farmer, using cover crops and combinations of cover crops recommended by your local University Extension agencies will work wonders.

There’s lots of research going on right now via the USDA and various universities around the country as to exactly what types of cover crops work best with the aim of helping more farmers get off the “chemical treadmill” and reduce pollution.

A soil profile showing biologically active soil beginning to regenerate. A Jerusalem artichoke sprouts through the surface of this young no-till bed that’s been mulched with leaf litter and  wood chips.

5. Utilize biodiversity.

What does it mean to “utilize biodiversity”? In large farms, this might mean crop rotation and intercropping. On smaller farms, it might mean developing high-yielding food forests with hundreds of species of plants and animals mixed in.

If you’re a gardener, you can actually develop far more biodiverse, resilient agroecosystems than a large farmer could ever dream of and even utilize edible landscaping approaches to make your food system attractive to neighbors. 

A Monarch butterfly getting nectar from a Zinnia (foreground) as our Welsh Harlequin ducks forage in the background. Countless species visit and live in our garden system, and we're the clumsy conductors of that orchestra.
A Monarch butterfly getting nectar from a Zinnia (foreground) as our Welsh Harlequin ducks forage in the background. Countless species visit and live in our garden system, and we’re the clumsy conductors of that orchestra.

Research has shown again and again, that the more plant diversity you have:

  • the more microbial diversity you have in your soil system,
  • the more (and more varied) your beneficial insect communities will be, and
  • the less likely you are to have severe infestations of pest insects or plant pathogens which tend to thrive in monocrop systems.

Best of all, diversity in your garden means you’ll always get a yield! If one type of plant has an off-year or gets killed, you’ll have other plants that will fill your harvest basket.

There should always be something to eat, even if one type of plant has an off year. Living in South Carolina, we get to harvest fresh organic food from our garden 365 days of the year.
There should always be something to eat, even if one type of plant has an off year. Living in South Carolina, we get to harvest fresh organic food from our garden 365 days of the year including in the fall and winter.

Now you know how and why synthetic nitrogen fertilizer causes pest insect infestations in your garden. You also know a better path forward to feed your plants.

So put the fertilizer down and start focusing on the biological fertility of your soil!

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One Comment

  1. I appreciate you providing some basic tips in building biological soil fertility in your garden or farm. Honestly, I don’t really know much about this topic but It’s good to know that you mentioned avoiding the use of different kinds of pesticides which may be harmful to your plants. It’s still best to use those that are approved by OMRI. I will definitely read more articles about fertilizers and its benefits to soil fertility. Thanks.

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