Nematodes

What Are Nematodes?

Nematodes are microscopic roundworms that belong to the phylum Nematoda and are naturally found in soil across the world. Most species are free-living and play a role in healthy soil ecosystems, breaking down organic matter and providing food for other organisms. A smaller group are parasitic nematodes: these are the ones used in biological pest control.

Insect parasitic nematodes actively seek out host insects in the soil, enter the body through natural openings, and release bacteria that kill the host within a few days. The nematodes then multiply inside and move on to find new hosts. They are species-specific, meaning the nematodes you buy for vine weevil larvae will not harm beetles, bees, or other insects. This precision is what makes them such a strong fit for organic gardening and wildlife-friendly gardens.

Quick Wins: Getting the Most from Nematodes

• Match the product to the pest. Nematodes are not a general pesticide. Each product is formulated for a specific pest or group of pests.
• Check soil temperature first. Most species need soil above 5°C; some low-temperature vine weevil options cope with cooler conditions.
• Apply in damp conditions. Nematodes need moisture to move through soil. Water before and after treatment, then keep the area moist for two weeks.
• Apply in the evening or on a dull day. UV light reduces survival on the soil surface, so low-light conditions give a better result.
• Don't store them too long. These are living organisms. Keep packs refrigerated and use before the expiry date. Most have a shelf life of around two weeks once mixed.
• Reapply regularly. A single treatment can work for several weeks, but six-week reapplication intervals are recommended during heavy pest pressure.

Tips for Best Results

Nematodes work below the surface, so they are most effective when applied before visible damage becomes severe. For soil-dwelling pests like vine weevil grubs and chafer grubs, timing the application to coincide with young larval stages gives the best outcome: older larvae are harder to kill.

For pests that move between soil and plant surfaces, such as codling moth and box tree caterpillar, application directly to bark crevices or the base of affected plants helps the nematodes make contact with larvae before they pupate.

Combine nematodes with habitat management where possible: reducing heavy debris, leaf litter, and damp hiding spots cuts down the conditions that many pests need to thrive.

Beneficial Nematodes and Organic Gardening

Biological pest control with nematodes is well suited to organic-style growing. They leave no chemical residue in soil or on harvested produce, they are approved for use in organic gardening systems, and they have no recorded harmful impact on native plants, other wildlife, or soil health when used as directed. For growers wanting to reduce reliance on pesticides, nematodes offer a targeted, lower-impact way to manage some of the most damaging soil-dwelling pests through the growing season.

Frequently Asked Questions

Are nematodes safe for pets, children, and wildlife? 

Yes. Beneficial nematodes are safe around children, pets, birds, and other wildlife when used as directed. They target specific insect or slug species and do not affect mammals, birds, or plants.

Can I use nematodes in a greenhouse? 

Yes. Several nematode species are particularly well suited to greenhouse use, including those for fungus gnats, sciarid fly, thrips, and housefly. Apply to the growing medium and keep it moist after treatment.

How do I apply nematodes? 

Mix the pack with water according to the label, then apply with a watering can fitted with a coarse rose, a hose-end applicator, or a sprayer on a coarse setting. Water in afterwards and keep the soil moist for two weeks.

Are nematodes a form of biological control?

Yes. Nematodes are one of the most widely used biological control methods in UK gardening. They are living organisms that target specific pests naturally, without chemical residues, making them a strong fit for organic and wildlife-friendly growing.

Are nematodes better than slug pellets? 

For below-ground slug control, nematodes are generally the stronger option. They target slugs in the soil where most feeding and egg-laying happens, leave no chemical residue, and are safe for wildlife, children, and pets.Read our nematodes for slugs blog for a full breakdown, or see our guide to slug pellets if you want to compare approaches.