How to Plant a Biocontrolled Garden to Regulate Pests
How do you keep aphids, hornworms, and other garden pests in check without nasty sprays or tedious hand-picking? Nature’s ancient food webs can help you create a self-regulated garden that acts like a natural ecosystem. Biocontrol, or biological control, is a pest-control method using natural predators and other organisms to keep pests in check.
Many people think all bugs are bad, but entomologists estimate that only 1 to 3% of all insects are pests. Most garden bugs are beneficial, particularly those with a voracious appetite for the pests that attack your crops.
When combined with other integrated pest management strategies, biocontrol principles (also called biological control) can help cultivate a naturally pest-resistant garden where predatory insects do the hard work of pest control with little intervention from you. But first, you must lay the groundwork for a biocontrolled garden that magnetizes the “good guy” bugs and keeps the bad ones in check.
Let’s dig into everything you need to know about using biocontrol in your organic garden!
What is Biocontrol?
Biological control, or biocontrol, is a pest management strategy that relies on natural predators to control pests and diseases in an agricultural system. For example, biocontrol involves using ladybugs to control aphids or planting white alyssum to attract parasitic wasps that attack tomato hornworms. Biocontrol can also involve introducing wolves into areas with out-of-control deer populations, using a virus to kill large infestations of rodents, or introducing bacterial agents to handle some pest management.
In the garden, biological control is an exciting and cheap way to harness the power of ecology and science! Fortunately, it doesn’t have to be as complex as it sounds. The process mostly involves choosing the right plants and monitoring pest populations.
Instead of destroying all insects and microorganisms with chemical sprays, a biocontrol strategy welcomes the beneficial organisms and helps them establish populations in the garden. Once proper habitat is established, biocontrol becomes like a built-in pest management system that operates 24/7 without human intervention.
This ecological method mimics nature’s systems of pest management. In the classic case of a mountain lion and hare (rabbit), both species continuously balance their populations.
When the prey species (the hare) skyrockets in numbers, the abundance of food prompts an increase in predator populations (the lions). If the predator populations outpace the rabbits, a lack of food for the mountain lions will reduce their litter size and bring populations down.
In any predator-prey dynamic, the two species exist in a perpetual dance where both populations depend on the other. Of course, almost every species has multiple interactions with others, which means a complex food web exists at every level of the food chain.
While you probably don’t have any mountain lions controlling the rabbit or rodent population in your garden, you can apply the same principles to pest control.
Just like an animal, every insect and bug has its place in a food web of predators and prey. Things get interesting when you factor in parasites that can be used as biological warfare against anything eating your crops.
Ecological Checks and Balances
In other words, biocontrol is all about ecological checks and balances. Wild ecosystems naturally control themselves. The unspoken rules of biology and ecology operate in a way that constantly seeks homeostasis or balance.
Things get out of whack only after human disturbance and intervention. Rabbit populations in suburbia are only out of control because the habitat of local mountain lions, coyotes, and bobcats has been developed into neighborhoods and malls.
This macro-level example describes what is happening at the tiny leaf level with a pest like aphids. A garden effectively destroys all the natural predators of aphids by planting only the crops aphids like to snack on. Without the habitat for ladybugs, lacewings, parasitic wasps, hoverflies, and other aphid-eaters, the pest can multiply rapidly like the bunnies in your yard!
Pests Multiply Faster Than Predators
To make things more complex, we typically import non-native plants from faraway lands or cultivate seed varieties that don’t exist in our local habitats. This can be enticing for pest insects, especially when it’s something they especially love.
Pests evolve more quickly than predators because they have a very short lifespan. For example, one aphid can birth up to 80 offspring per week, and it only takes 7-8 days for a newborn nymph to mature into an adult. Often, they don’t even need sexual reproduction! The females are born already pregnant as exact clones of their mothers. No wonder an infestation gets out of hand so quickly!
Fortunately, predators have an evolutionary advantage up their sleeve. Although mountain lions, wolves, bears, and other large predators have longer life cycles and produce fewer offspring (which means slower evolution), they eat a lot at a time. This is their unfair advantage!
Similarly, a lady beetle (ladybug) has a lifespan of about a year and lays about 1,000 eggs in her lifetime. While she may not keep up with the outrageous reproductive capacity of an aphid, she is larger and hungrier.
An adult ladybug eats 50 to 60 aphids daily, and a developing ladybug larva eats up to 100 aphids daily! Even though a ladybug’s life cycle takes much longer than a pest, you can see how these voracious predators can still keep the ecosystem in check.
Beyond Insect Biocontrol
Interestingly, biocontrol doesn’t only use insects. For example, Bt is a popular organic spray in which is suspended a bacteria called Bacillus thuringiensis. This form of biological control uses a bacterial pathogen to control a pest.
Similarly, cutting-edge research uses biocontrol fungi like Ampelomyces quisqualis as a foliar spray to fight off pathogens like powdery mildew and rust. Imagine the invisible warfare happening at the microscopic level!
In this case, a beneficial fungus is attacking and infecting the disease-causing fungi, rebalancing the leaf microbiome. There is an entire ecosystem of predator and prey microorganisms battling for survival, just like the mountain lion and the hare.
Types of Biocontrol
Biocontrol is a modern science-backed approach to pest control, but how does it play out in a real-world environment? It depends on which type of biological pest management you employ!
For decades, scientists have worked with farmers, biologists, and wildlife managers to harness the power of biological control to supplement or replace other methods. Farms worldwide have eliminated most pesticides by implementing biological control strategies as part of their IPM (or integrated plant management) systems.
Essentially, we aim to “undo” some of the ecological damage and disruption caused by us humans. You can easily apply these principles to even the smallest garden. But first, you must understand the three different types of biological control:
- Conservation Biocontrol
- Classical Biocontrol
- Periodic Release Biocontrol
This is the most important form of biocontrol for an organic gardener. It is all about building a habitat that attracts native predator insects that already live in your area.
In other words, you aim to conserve native resources and habitat to attract the beneficial predators that will keep your crop pests under control.
On a farm, this can be as simple as letting some field margins grow wild. In a garden, you can get far more detailed with your landscaping to create a thriving oasis of biodiversity and natural pest control. As a bonus, conservation biocontrol can be absolutely beautiful.
Rather than importing and releasing insects (described below), conservation biocontrol magnetizes natural enemies and encourages them to stay in your garden. This creates long-lasting cycles of pest management because the predators live in your yard for many generations.
Of course, it takes time to build up populations enough to fully control pest problems you may have. This process starts by building the habitat. You must plant the herbs and flowers that beneficial insects like so they are drawn to your garden.
Most beneficials do their pest-destroying favors in their infancy or larval stage. But you must first attract the adults (beetles, flies, moths, etc.) to lay the eggs and begin the cycle of biological control.
Allowing Some Pests
Paradoxically, conservation biological control requires you to let some pests run their course. In the beginning, there may not be much food for predator insects. This is especially problematic if you have wiped out pest populations with a pesticide.
For example, let’s say an adult syrphid fly (hoverfly) comes to your garden because you are growing dill and Queen Anne’s Lace. The adults are not predaceous; they feed on your plants’ nectar, pollen, and honeydew. But when it’s time for them to reproduce, they’ll lay eggs on those host plants (in this case, Liliaceae or lily family members).
Their larvae will emerge, hungry for aphids, scales, caterpillars, and mites. But, if you kill all the scale pests with neem oil, there won’t be anything for those larvae to eat.
The predators may move elsewhere, like a nearby wild field, to produce future generations because your garden doesn’t have the bugs they need. Similarly, ladybug populations won’t stick around if there aren’t enough aphids to eat.
The early stages of conservation control are where trap cropping could be beneficial. A trap crop is a pest-attractant like radishes or kale that you plant on the margins of your garden.
Pests like aphids or flea beetles are drawn to the area and colonize the plant. They provide some food for early emerging predators. Then — before things get out of hand — you destroy it by pulling it out, throwing it away, burning it, or otherwise killing all the pests.
This is particularly beneficial in the spring when pests emerge from dormancy and may have a big boom in population. However, if you forget about your trap crop, this method can be disastrous because you create a hub for pest reproduction rather than a means of control.
Once your biocontrolled garden is established, you won’t have to worry about trap cropping or huge infestations.
- Long-term pest control
- Native predators colonize your garden
- No need to purchase or release insects
- You can establish a garden with zero need for sprays or pesticides
- Takes time to establish beneficial populations
- Some pests must be allowed to feed predators
- Presence of native predatory insects depends on your surroundings
- You may lose some crops to pests during the early stages while the ecosystem finds balance
While conservation biological control aims to welcome and conserve native predators, classical biocontrol introduces predators from outside the area. In some cases, this is an exotic agent not native to the region.
For example, the cottony cushion scale pest devastated California’s citrus trees in the late 1800s. Scientists discovered two predator insects (the Vedalia beetle and a parasitoid fly) in Australia and introduced them to California. The exotic predators quickly took hold and eliminated the cushion scale. This was a success!
Clearly, there was a lot of risk in this endeavor. What if the Vedalia beetles overpopulated and killed all the native beetles, creating another ecological disaster? Or, what if the imported control agent ate some of the pests but ran out of its natural food and died or left the area?
This method is more complex because it is a guessing game. You may be familiar with invasive weeds and ornamental plants that displace native species. Nobody knew they were going to be invasive until it was too late!
Classical biocontrol is not typically recommended on a home scale. However, you can sometimes order predator insects from accredited online sources.
- Can control pests on a very large scale
- Fast-acting control
- Predators released in mass numbers
- Not very viable on a home scale
- Predators may not stick around
- Predatory insects could multiply and displace native insects
Mass Rearing and Periodic Release
Finally, we reach the type of biological control that provides fairly instant gratification. Mass rearing means insect predators like ladybugs or parasitic wasps are raised in huge quantities in a lab. A gardener or farmer orders the insects and releases them into a confined space, such as a greenhouse or small garden.
If you release live insects, the predators quickly go to work, taking down the population of aphids, hornworms, flea beetles, Japanese beetles, squash bugs, or whatever pest you’re dealing with! It is cheaper (and sometimes less squeamish) to release larvae or eggs that can hatch and work their magic.
There are specific predators for nearly every garden pest, but they are most effective when combined. This way, you aren’t relying on only lacewings or only ladybugs to tackle your pest outbreak.
For example, a simple Google search for “buy beneficial insects online” reveals dozens of mass-reared predatory species available for purchase and release. Many companies offer blends of aphid predator larvae, fungus gnat predators, caterpillar parasites, or beneficial nematodes. You can certainly experiment with these products, but it can get expensive if you don’t know what you’re doing.
The major downside to periodic release is the risk of beneficial insects leaving your neighbor’s yard or a nearby wooded area. They won’t stay in your garden if you don’t have the resources they need. However, if you establish a conservation biocontrol area, this can be effective for jumpstarting your garden’s beneficial insect populations.
Still, all your money and effort can be wasted if the predators decide not to stick around. This is why I recommend conservation biocontrol; the insects are native to your area, and establish a home base in your garden for reliable pest control for years to come.
- Quickest method for instant bio pest control
- Ideal for small, confined areas
- Blends (“guilds”) of predators can be ordered together for a specific pest
- Many species of adults and larvae are widely available
- Can be quite expensive
- Predators could fly away and seek other nearby resources
- Predators may not stay in your garden over the long-term
- Requires more knowledge of predator-prey dynamics
Don’t worry, you don’t have to choose just one method! In fact, a combination of pest control methods is the ideal form of integrated pest management.
While conventional gardeners may rely solely on sprays that kill all the beneficials, creating an endless cycle of pesticide dependency — ecological gardeners have a whole arsenal of natural controls up their sleeves!
How to Plant a Biocontrolled Garden
The science of biocontrol can seem pretty intimidating, but the practice doesn’t have to be complicated. Now that you understand the basics, here’s how to integrate these strategies into your garden so you don’t have to worry about pest outbreaks.
Biodiversity is Key
The research is clear: More biodiversity creates more resilience. Conversely, the global loss of biodiversity is directly linked to reduced ecological resilience. In other words, a lack of diversity makes an ecosystem more vulnerable to disturbance, like pests, diseases, or drought.
We must start thinking of our gardens as mini-ecosystems to harness the power of biological pest control. Nature inherently wants diversity. You rarely see a native forest of only one type of tree. The ecosystem includes hundreds, if not thousands, of plants, animals, and microorganisms working together to create balance and harmony.
If one single species monopolized the area, it would be extra susceptible to a decimating pest or disease. This is why a huge plot of one type of crop, like squash, can be decimated so quickly by squash bugs. It’s like a big sign that says, “Hey, pests! Look over here! We have a ton of easy food and zero predators!”
No wonder monoculture fields of thousands of acres of corn are so heavily sprayed with pesticides! The natural ecosystem is so heavily disturbed that the crops can only function with continuous human and chemical intervention. This same concept applies to forests, deserts, cities, farms, gardens, and anywhere else on Earth.
Build a healthy ecosystem
To make your garden more self-sufficient, like a healthy ecosystem, consider biodiversity from two distinct angles:
- From a pest perspective, you want as many diverse crops as possible to confuse pests.
- From a predator angle, you want to attract a range of beneficial insects with many different food and habitat resources.
Action Step: Take a diversity inventory of your garden. Address diversity on every level:
- Grow several different seed varieties of each type of crop (for example, curly kale, Russian kale, and Lacinato kale).
- Plant multiple species together in the same beds.
- Practice crop rotation for diversity through time.
- Choose plants that flower at different times throughout the season.
- Practice succession planting (sowing multiple rounds of each crop).
- Avoid planting large clusters of the same plant family together (for example, a huge plot of cucumbers right next to summer squash).
- Utilize garden borders for perennial herbs, flowers, and native plants.
As a bonus, diversifying your garden diversifies your plate! Experiment with new vegetables, herbs, and fruits in the kitchen so you can add them to your garden.
Avoid Chemical Pesticides
This may seem obvious, but to magnetize beneficial insects, you should avoid excessive use of pesticides of any kind. Even overuse of organic methods or biocontrol sprays can be negative. Small spot uses of organic sprays are OK, but chemical pesticides are off the table if you wish to create a truly biocontrolled garden.
The problem with most synthetic pesticides is that they’re non-specific or “broad-spectrum.” This means they kill everything without any discrimination. Broad-spectrum pesticides wipe out the bad guys and the good.
This is especially problematic because, as mentioned above, the bad guy pests bounce back more quickly than slow-maturing predators. The result is a sort of “pesticide treadmill” where your garden relies on sprays because all the beneficial insects have been wiped out.
Exceptions include pesticides or sprays that specifically target a group of insects. These are called selective or “narrow-spectrum” pesticides. For example, Bt is a biocontrol bacteria that only impacts caterpillars and should not harm predator insects. However, you should not use Bacillus thuringiensis on your milkweed, as it will negatively impact your butterfly population.
Be mindful of your choices, and limit even organic methods to only when it’s absolutely required. If you can wait for your beneficial insects to handle the problem, do so!
Meet Your Beneficial Predatory Insects
It greatly helps to familiarize yourself with the types of beneficial bugs you want to see around your garden. There are far more predatory insects than the infamous ladybug! If you see these good guys flying or crawling around, it will give you confirmation on whether your biocontrol efforts are working or not.
The most common predatory insects in gardens include:
- Lady beetles (ladybugs): Both larval and adult stages voraciously consume aphids.
- Syrphid flies (hoverflies): Larval stages prey on aphids, thrips, caterpillars, and whiteflies
- Parasitic wasps: Parasitize tomato hornworms, cabbage loopers, and leaf miners; harmless to humans.
- Lacewings: Larvae eat up to 1,000 aphids per day and also feed on spider mites, scale insects, and mealybugs.
- Tachinid flies: Eat or parasitize aphids, Japanese beetles, and squash bugs.
- Dragonflies: Prey on mosquitoes, midges, and other insects.
- Spiders: Opportunistic predators eat gnats, mosquitoes, thrips, or anything in their web.
- Big-eyed bugs: Eat flea beetles, aphids, mites, and small caterpillars.
- Soldier beetles: Larvae eat grubs, slugs, and snails. Adults eat aphids and mites.
Learn more about attracting and identifying these epic beneficial insects in our guide on 15 Beneficial Predators to Attract to Your Garden.
Plant Nectar Resources
Like pollinators, predatory insects need nectar sources to meet their nutritional needs. Although many beneficials eat the most pests during their larval stage, you must feed the adults to encourage them to lay eggs in your garden.
Some of the best nectar-producing flowers for beneficial insects include:
- White Alyssum
- Queen Anne’s Lace
- Dill (flowering)
- Fennel (flowering)
- Bee Balm
- Black-Eyed Susan
- Lemon Balm
- Butterfly Bush
- Bachelor’s Button
As you can tell, many of these flowers overlap with the favorite plants of bees and butterflies. As you build a biocontrolled garden, you can simultaneously attract more pollinators!
You want to plant these nectar-rich flowers as close to your crops as possible. This ensures that a cabbage looper or aphid snack will only be a short hop away from home base. Interplanting white alyssum and marigolds within a bed of tomatoes or peppers is ideal.
In a raised bed, I like to use the “four corners” method, where I put a beneficial flower or herb in each corner of the bed so they won’t interfere with crop growth.
You can also build perennial border beds close to your vegetable garden. A few feet of pathways is nothing to worry about. As long as the nectar resources are within a “stone’s throw,” predators should have no problem reaching their prey.
Plant Pollen Resources
In addition to nectar, predatory insects need pollen for protein and other nutrients. Like bees, many species feed this pollen to their larvae, encouraging more pest-eating action! Many of the above species provide both nectar and pollen, but a few additional resources never hurt.
Great pollen-producing plants include:
- Wild buckwheat
- Basil (flowering)
- Wild sunflowers
- Wild lupine
- Goldenrod (Solidago)
Once again, these plants can dual-function as food for butterflies and bees!
Prioritize Native Plants
The recent resurgence of interest in native plants is great news for local ecosystems. If you aren’t already, consider planting native species in your garden to attract native insects. This is true conservation biocontrol because you are conserving the natural habitat of your resident predators rather than importing exotic species.
Native plants are inherently adapted to your region and can thrive with very few external inputs. They provide more food and habitat for ladybugs, parasitic wasps, lacewings, beetles, and beyond.
These excellent species are native to the United States:
- Joe-Pye Weed (Eutrochium spp.)
- New England Aster (Symphyotrichum novae-angliae)
- Blue Wild Indigo (Baptisia australis)
- Swamp Milkweed (Asclepias incarnata)
- Dutchman’s Pipevine (Aristolochia macrophylla)
- Eastern Bluestar (Amsonia tabernaemontana)
- Golden Alexander (Zizia aurea)
- Wild Bergamot (Monarda fistulosa)
- Spicebush (Lindera benzoin)
- Eastern Red Columbine (Aquilegia canadensis)
- Ohio Spiderwort (Tradescantia ohiensis)
- Virginia Mountain Mint (Pycnanthemum virginianum)
- Blazing Star (Liatris spp.)
- Sneezeweed (Helenium autumnale)
- Purple Giant Hyssop (Agastache scrophulariifolia)
- Swamp Sunflower (Helianthus angustifolius)
- Wild Blue Phlox (Phlox divaricata)
- Cardinal Flower (Lobelia cardinalis)
- Boneset (Eupatorium perfoliatum)
Try to find species and varieties indigenous to your region. Look for local native plant nurseries to buy established plants or sow wildflower seed blends specifically formulated for your area.
Aim for Year-Round Resources
Add Insect Hotels
Insect hotels are quirky little boxes or structures that provide places for insects to overwinter. They can be cute and aesthetic or simple and wild. Each species of beneficial predator has different nesting requirements, but some general ideas include:
- Stacked firewood
- Piles of hollow bamboo canes
- Layers of straw, dried grass, or rolled-up cardboard
- Bundles of sticks and twigs
- Rotting logs
- Wood with holes of different sizes drilled into it
- Bricks with holes in them
Imagine tiny crevices or natural spaces where bugs can hide and keep warm. Insect hotels don’t need to be anything fancy! However, they are particularly important in cold climates where insects may die out or migrate south for the winter. You want to keep the good guys around so they can emerge in the spring when pests start creeping out.
Include a Water Source
Most gardeners are very in tune with the water needs of their plants, but we forget that our resident insects need water, too! If you’re already panicking about attracting mosquito swarms to your garden, rest assured that beneficial predators don’t need large bodies of water to support them.
Keep it simple with:
- A Bird feeder
- A Shallow bowl of water
- A Mini fountain
- A Gravel-filled dish of water
To prevent mosquitoes, change the water every few days or dump it out and allow rain to refill the container. As long as the area doesn’t stay stagnant, it can serve as a freshwater source for good guys rather than blood-sucking pests!
Mulch and Compost
Adding compost and mulch to your garden beds is already an incredible practice for enriching your soil and keeping weeds at bay. Additionally, these layers of organic material provide space for predators to hide out and multiply.
Straw mulch is particularly beneficial for controlling beetles. I always mulch heavily around crops like squash, potatoes, and perennials to keep the moisture in and prevent weeds. Fortunately, the straw also provides habitat for spiders, assassin bugs, and predatory ground beetles that help keep Japanese beetles under control.
Practice Companion Planting
Companion planting is very compatible with biological pest control because it maximizes diversity and naturally repels pests. This age-old technique combines complementary plants to save space, deter pests, attract beneficial insects, improve yields, and/or provide structural support (like beans vining up a corn stalk).
Moreover, companion planting helps you diversify your beds without impeding one crop’s growth. A key consideration is the growth habit of each plant.
For example, lettuce is a great companion for tomatoes because it grows low to the ground and enjoys the shaded canopy of tall-growing tomatoes.
Similarly, borage is a great companion for zucchini because it will attract pollinators to improve squash yields, yet it is robust enough to hold its own amongst big squash plants.
Remember, diversity is often an organic gardener’s most effective pest management strategy. We should never rely on a single practice. Putting all your eggs in one basket (i.e., relying on a single strategy like companion planting) can lead to disappointment and even complete crop loss.
Instead, you can create several layers of “insurance” against the bugs. If your wildflowers fail to germinate, backup flowers are blooming from your perennial beds.
If your parasitic wasp populations fail to take off, you always have the hoverflies that overwintered in your insect hotels. The more methods you can “stack,” the more ecological resilience you build!
Set a Pest Threshold and Use Alternate Methods
Before you embark on your biocontrol journey, you must ask yourself what level of pest damage you will accept on your vegetables. I’ve seen the most pristine, flawless produce harvested from an ecological garden. But I’ve also seen gardeners struggle with ugly veggies in the early stages because their predator populations aren’t yet established.
For example, you may decide that the flea beetles on your arugula are getting too out of hand, and you aren’t willing to wait for the ladybugs or beneficial nematodes to work their magic.
In this case, you may employ alternative methods to protect your crops. Row cover is my favorite way to protect young greens from pests. Simply drape a floating row cover over the bed right after seeding or transplanting.
In another case, you may be getting frustrated by colossal populations of aphids that your newly establishing beneficial populations can’t get a handle on. You may give your plants a hard blast of water or apply horticultural soap to wipe off areas of major infestation. This can buy you some time while predator populations catch up.
Lastly, remember that biocontrol is not a quick fix for pest problems. However, it can be a reliable long-term strategy for improving pest control. Like many organic methods, it takes several seasons to establish a thriving garden ecosystem. There will be challenges and learning experiences along the way, but rest assured that it gets easier every year! Remember, not all bugs are bad! The good guys are here to help you.