The Best Way to Keep Grubs Out of Your Garden—Without Using Harmful Pesticides

Grubs, the larval stage of beetles such as Japanese beetles and June bugs, are notorious garden pests that feed on the roots of cherished plants and grass. These garden nightmares can cause significant damage, leading to sickly plants because the severed roots eaten by the grubs can no longer absorb water and essential nutrients.

If you’ve faced this issue, you know firsthand how devastating it can be. Fortunately, there’s a safe, natural method to protect your plants from pest damage without resorting to harmful chemicals. By introducing beneficial nematodes, a natural biological agent, you can effectively eliminate your grub problem while ensuring the safety of people, pets, and pollinators.

Ahead, experts will explain what nematodes are, the benefits they bring to the garden, and how to apply them successfully to keep grubs far away from your plants.

Why Nematodes Are the Best Grub Repellent

Beneficial nematodes are a natural and effective solution for controlling grubs without the need for chemical pesticides, says Jamie Schwartz, field technician at Nature's Good Guys. "Think of them as tiny, smart hunters that only go after the pests that can damage plants, while leaving your earthworms, plants, and pets totally alone," she says.

While chemical sprays can be harsh on the environment, Schwartz notes that nematodes do the job naturally while keeping the soil's ecosystem in balance. "It’s the easiest way to handle grub populations safely and sustainably," she says. "Instead of using synthetic chemicals, introducing a natural biological agent to protect the yard and garden is a win-win strategy."

How Nematodes Keep Grubs at Bay

Think of beneficial nematodes as a natural "seek and destroy" team for your soil. "These tiny worms hunt down grubs and move inside them to release a specific bacteria that stops the grub from developing within just a few days," Schwartz says. Once the grub is parasitized, the nematodes use it as a food source and incubator, producing a whole new generation of beneficial nematodes to find remaining pests.

When to Apply Beneficial Nematodes

To maximize the benefits of nematodes, they must be applied at the proper time. Schwartz recommends applying beneficial nematodes in the spring or fall, when grubs are young and hanging out near the soil surface.

In spring, wait to apply the nematodes until the soil warms up to about 50 to 60 degrees Fahrenheit. In the fall, release nematodes to hedge against newly hatched grubs as they move toward the soil surface.

"Beneficial nematodes are sensitive to the sun, so it’s best to release them on a cloudy day, early in the morning, or in the evening," says Schwartz. When applying nematodes, it’s essential to keep the soil moist so they can move around easily to find grubs.

How to Apply Beneficial Nematodes

Now that you understand when to apply beneficial nematodes, the next step is to ensure they are applied correctly. "To ensure these microscopic organisms thrive and find their targets, the application must focus on hydration and protection from UV light," says Brandon T. Kail, founder of Rocky Mountain BioAg. Here, he shares straightforward instructions to ensure your nematode application is successful.

Prep the Soil

Nematodes move through the film of water surrounding soil particles. Water the garden or lawn thoroughly 24 hours before application to ensure the "highways" are open for them to travel.

Timing Matters

Apply nematodes in the early morning or at dusk. "They are extremely sensitive to UV light; direct sunlight can kill them in minutes before they have a chance to burrow into the soil," says Kail. Cloudy, rainy days are also ideal.

Mixing and Equipment

Mix the beneficial nematodes with water, following the instructions on your product for the proper ratio. Use a garden sprayer, a watering can, or a hose-end sprayer to apply the nematodes effectively. If using a sprayer, Kail recommends removing any fine filters or screens (usually 50-mesh or finer), as nematodes can get stuck in the mesh and perish.

Follow-Up

After application, lightly water the area again. This "washes" the nematodes off the foliage and into the root zone where the grubs live.

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How Often to Apply Nematodes

How often you apply beneficial nematodes to your garden depends on the severity of the infestation and the health of your soil biology, says Kail. By keeping these ideal application windows in mind, you can ensure you're on the right track.

• Ideal window: A once-a-year application in early fall is the most effective. This is when grubs are small, active, and near the surface.
• Preventative approach: If you have a history of heavy grub pressure, Kail notes that a second application in late spring can help catch any larvae that survived the winter before they emerge as adult beetles to lay more eggs.
• Long-term maintenance: Once a healthy biological balance is thriving in the soil, Kail explains that you may only need to apply them every two to three years or potentially never again.

Mistakes to Avoid When Applying Nematodes

Since you are working with live biology rather than a dormant chemical, Kail advises that certain errors can render the treatment ineffective. Fortunately, these helpful tips will help you avoid these mishaps.

• Applying to dry soil: Never apply nematodes to dry soil, as nematodes cannot move and will quickly dehydrate and die, says Kail. Always water the soil before application.
• Ignoring soil temperature: Nematodes are most active when soil temperatures are between 55 and 85 degrees Fahrenheit, says Kail. "Applying them too early in a cold spring or during a mid-summer heatwave can result in high mortality rates," he says.
• Improper storage: Nematodes are perishable. Kail recommends storing them in the refrigerator until the moment you are ready to mix and apply them. Check the "best by" date on the package, and never store them in the freezer.
• Mixing nematodes with chemicals: Avoid using synthetic fertilizers or fungicides with your nematode application, as these harsh inputs can shock or kill the nematodes. Kail recommends waiting for at least two weeks between a chemical application and a biological one. "The best approach is to only mix and use fertilizers and inputs that are beneficial to your soil’s microbiome; staying away from fertilizers and fungicides that harm soil life," says Kail.
• Letting the solution sit: Once the nematodes and water are mixed, they begin to use up their limited oxygen supply. Kail recommends applying the entire mixture within 30 to 60 minutes of mixing to ensure it is at peak vitality when it hits the soil.