If you have lived in Ottawa for more than one summer, you know the heartbreak of seeing your prize-winning roses look like they’ve been through a paper shredder. The culprit is the Japanese Beetle, a shimmering green iridescent pest that treats your garden like an all-you-can-eat buffet. While we usually notice them in July, the real battle is won right now, deep beneath the surface of your lawn.
Spring is the prime window to deploy our secret weapon: Beneficial Nematodes. These microscopic "garden ninjas" hunt down beetle larvae (grubs) before they can ever grow wings and find your hibiscus. Since the soil in the Ottawa valley is finally warming up to that sweet spot of 10-15 degrees, it is officially time to act.
For the New Gardener: What are these things?
If the idea of putting "worms" on your lawn sounds a bit counterproductive, but don’t worry! Nematodes are naturally occurring, microscopic organisms that are completely harmless to people, pets, and even earthworms. They are specifically designed to seek out and destroy the "grub" stage of the beetle.
To get started, you’ll want to pick up a pack of Lawn Guardian Nematodes from our shop. Since these are living creatures, they have a few requirements for survival that you need to follow:
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They must stay refrigerated until the moment you use them.
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They hate the sun, so you should only apply them at dusk or on a very cloudy, rainy day.
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They need a "water highway" to travel through the soil, so your lawn must be soaked before and after application. Think about applying them after a good rain!
How to Optimize the Hit
For Japanese Beetles specifically, the species Heterorhabditis bacteriophora (often abbreviated as Hb) is your best bet because they are active "cruisers" that hunt deeper in the soil than other varieties.
The spring window is shorter than the fall one, as you are trying to catch the larvae after they wake up from their winter slumber but before they pupate in June. To ensure your Nematode application is a total success, keep these technical factors in mind:
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Check your soil temperature with a probe to ensure it is consistently above 10-15 degrees at night.
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Talk to your neighbours! Using nematodes as a community can help significantly reduce the population of these destructive pests!
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Remove any filters or fine mesh screens from your sprayer, as these can actually "squish" the nematodes before they hit the grass.
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Avoid using high-nitrogen fertilizers for at least two weeks before and after, as high salt levels can dehydrate your microscopic army.
Nematodes are easy to apply, safe, and beneficial for your lawn! If you're not sure if it's grubs that are responsible for making your lawn look "scorched", there are a couple ways to check!
You can try the "carpet" test. If you've located a part of your lawn that feels "spongy" or looks more discoloured, try pulling up a patch of brown grass as if you were checking under a carpet. If you can easily lift the turf, grubs have likely eaten the root system.
Notice signs of wildlife damage. Holes from skunks, birds, and raccoons are often a more obvious sign of grubs than the grass damage itself.
The most effective way to determine if you have an infestation is to do a Grub count. Peel back a square foot of sod. If you see more than 5–10 C-shaped white larvae, it's time to take action!
A few last notes...
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The Ottawa Timeline: Generally, the first two weeks of May are the "Golden Zone" for spring application in our region. If you wait until the lilacs are in full bloom, the grubs may already be transitioning into pupae, making them much harder to kill.
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Nematodes aren't a "one-and-done" fix. Because adult beetles can fly in from your neighbour’s yard, it’s best to treat your lawn every spring and fall for three consecutive years to truly break the local population cycle.
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Storage: If you buy your nematodes today but it's a scorcher tomorrow, keep them in the veggie crisper! They can survive in a dormant state in the fridge, but they’ll perish quickly in a hot garage.