Beneficial Nematodes: How to Use Them for Gardening

Nematodes are tiny worms that inhabit the soil and attack the larvae and pupae of harmful insects. Some species of nematodes, known as beneficial nematodes, can be used by gardeners and farmers as an organic and eco-friendly form of pest control. Beneficial nematodes provide an effective way to control common garden pests without the use of chemical insecticides.

What Are Beneficial Nematodes?

Beneficial nematodes are non-segmented roundworms that occur naturally in soil and attack soil-dwelling insects. There are thousands of species of nematodes, but the two main types used for biocontrol of garden pests are:

  • Steinernema – attack insects that live in soil
  • Heterorhabditis – attack insects in soil, as well as above ground

These beneficial nematodes form a symbiotic relationship with bacteria in the genus Xenorhabdus. The nematodes carry the bacteria in their intestines and release them when they enter an insect host. The bacteria multiply and release toxins that kill the host within 24-48 hours.

The nematodes then feed on the bacteria and host tissues, reproduce, and emerge from the dead insect in search of a new host. The nematodes complete their life cycle within the infected insect. They do not harm earthworms, pollinators, or other beneficial insects.

Why Use Beneficial Nematodes?

Using beneficial nematodes can offer several advantages over chemical pesticides:

  • Organic pest control – Nematodes provide a natural, chemical-free way to control pests. They are OMRI-listed for organic use.
  • Safe – Nematodes do not pose risks to humans, plants, pollinators, wildlife, or the environment. They have no re-entry interval so plant picking can continue immediately after application.
  • Effective – When applied properly, nematodes quickly kill many destructive soil-dwelling pests at the larval or pupal stage. A single application can provide protection for an entire season.
  • Broad-spectrum activity – Nematodes target a wide range of common garden pests, including fungus gnats, root weevils, cutworms, armyworms, wireworms, grubs, and more.
  • Convenient – Nematodes come packaged as easy-to-use sprays or soil drenches. No special equipment is needed for application.

How Do Beneficial Nematodes Work?

Beneficial nematodes are applied to soil or growing media, where they actively search for host insects to parasitize. When they find suitable larval or pupal hosts, the nematodes enter through natural openings and release their symbiotic Xenorhabdus bacteria.

The bacteria rapidly proliferate inside the host, releasing toxins that result in septicemia and death within 24 to 48 hours. Nematodes feed on the bacteria and dead host tissues, completing their juvenile to adult life cycle in 2-3 weeks.

Thousands of new infective juvenile nematodes are then released back into the soil to continue the cycle. Nematodes continue reproducing as long as suitable hosts are available. Their populations will decline when hosts become scarce.

Purchasing Beneficial Nematodes

Beneficial nematodes are sold by the million (M) or billion (B) active juveniles that are ready to infect host insects. They are available at many garden centers, online, or through agricultural supply stores. When purchasing, look for the following:

  • Quantity – Opt for at least 5 million for small applications or up to 20 million for larger treatments. Nematodes are perishable so only buy what you need for one use.
  • Species – Choose Steinernema for pests in soil or Heterorhabditis for the broadest spectrum activity. Some products contain both.
  • Freshness – Check the expiry date and opt for the freshest available. Nematodes have a short shelf life and should be shipped cooled.
  • Quality – Select reputable suppliers who ensure viability and prevent overheating during storage/shipping. Check reviews.
  • Habitat – Make sure the species matches the habitat of your target pest (soil vs. wood-boring, etc).
  • Price – While cheap products may be tempting, quality should be the priority when purchasing beneficial nematodes.

When to Apply Beneficial Nematodes

For best results, beneficial nematodes should be applied when host insects are at their most vulnerable stages:

Soil Dwelling Larvae & Pupae

  • Spring application targets overwintered pests as they become active.
  • Late spring to mid-summer targets newly hatched larvae.
  • Fall application helps control pests before they overwinter.

Wood-Boring Larvae & Pupae

  • Spring application targets larvae near the wood surface.
  • Mid to late summer targets newly hatched larvae deeper in wood.

Avoid extreme heat. Ideal soil temperatures for application are 50-90°F (10-32°C).

How to Apply Beneficial Nematodes

Beneficial nematodes come packaged in several ways:

  • Clay/gel suspension – Apply as a spray or soil drench.
  • Sponge pack – Soak in water then apply.
  • Powder – Mix with water to activate then apply.

Follow all label directions carefully to ensure maximum viability. When applying:

  • Keep nematodes cool before and during application. Do not allow them to overheat.
  • Apply early morning or at dusk to avoid hot sun. Irrigate area before and after.
  • Use sufficient spray volume to thoroughly coat soil surface or reach pest location. Avoid runoff.
  • Agitate containers during application and use products promptly after dilution.
  • Reapply every 2-3 weeks until pest pressure subsides.

Nematodes can be delivered via:

  • Watering can, hose-end sprayer, or pump sprayer
  • Soil drench around affected plants
  • Injection into tree trunks, stems, etc for wood boring pests
  • Mist nozzle spray directed into pest harborage sites like soil cracks or mulched areas

What Pests Do Beneficial Nematodes Control?

Beneficial nematodes can provide safe, organic control of a wide variety of common garden pests:

Soil Pests

  • Ants
  • Armyworms
  • Carrot weevils
  • Chafers
  • Cutworms
  • Flea beetles
  • Fungus gnats
  • Root weevils
  • Scarab beetles
  • Strawberry root weevils
  • Symphylans
  • Thrips (in the soil)
  • Wireworms

Wood-Boring Pests

  • Bark beetles
  • Borers
  • Carpenter ants
  • Carpenter bees
  • Caterpillars
  • Grubs
  • Wood wasps

Other Pests

  • Crane fly larvae
  • Earwigs
  • Mole crickets
  • Sciarid flies
  • Sod webworms

Beneficial nematodes can provide season-long pest suppression after just a single application in many cases. However, they may be less effective against some pests like spider mites that spend limited time in the soil. Proper pest identification is key to selecting the right biological control agents.

Tips for Getting the Best Results

To maximize the effectiveness of beneficial nematodes:

  • Read and follow all label directions carefully regarding mixing, application method, temperature, timing, etc.
  • Only purchase the quantity needed for one use. Avoid storing diluted nematodes for more than 24 hours.
  • Apply early in the morning or evening when soil temperatures are between 50-90°F (10-32°C).
  • Thoroughly saturate the soil around and under plants to reach where pests are active.
  • Use nematodes in conjunction with other organic controls like horticultural oils or insecticidal soaps.
  • Improve drainage and aerate soil to allow nematodes to move freely to pests. Remove debris that can obstruct movement.
  • After application, irrigate gently to move nematodes deeper into soil. Avoid heavy watering that causes runoff.
  • Reapply every 2-3 weeks until pest populations are under control. Monitor for signs of reinfestation.

With proper selection, storage, application, and environmental conditions, beneficial nematodes can provide gardeners with an extremely effective method of controlling soil-dwelling and wood-boring pests without harmful chemicals. Their ease of use and broad activity make nematodes a worthwhile investment for anyone seeking to practice organic gardening and sustainable pest management.

Frequently Asked Questions About Beneficial Nematodes

What are beneficial nematodes?

Beneficial nematodes are small parasitic roundworms that attack soil-dwelling insect pests. Used in gardening and farming, they provide a biological form of pest control. Two main species, Steinernema and Heterorhabditis, are commercially available.

Are beneficial nematodes safe to use?

Yes, beneficial nematodes are non-toxic to humans, plants, and beneficial insects when used as directed. They are harmless if accidentally ingested. The bacteria they carry target only insects.

How effective are beneficial nematodes?

Very effective! When applied properly, nematodes can provide season-long control of target pests. A single application at the right time often controls pests through their vulnerable larval and pupal stages.

What pests do they control?

Nematodes target soil-dwelling pests like fungus gnats, root weevils, cutworms, and wireworms. Some species also attack wood-boring beetles, caterpillars, and other pests. They are less effective against mites and above-ground pests.

How long do beneficial nematodes last in soil?

Nematodes persist in the soil until they run out of hosts, which takes about 2-3 months under ideal conditions. Their populations decline in cold weather. Reapplication is often needed to maintain control when new pests emerge.

When should I apply beneficial nematodes?

Spring and fall application targets overwintering and newly hatching generations. Summer applications control larvae and pupae mid-season. Apply when soil temps are 50-90°F. Avoid hot midday application.

How do I apply beneficial nematodes?

Apply nematode suspensions as a soil drench or spray. Use sufficient water volume to thoroughly coat the soil surface or reach pest locations. Agitate the mixture during application. Follow all label directions.

What is the shelf life of beneficial nematodes?

Freshly shipped nematodes can survive for up to 3-4 weeks if refrigerated, but their viability declines rapidly as they age. Avoid buying more than you can use. Check for expiry dates and proper storage conditions.

How can I maximize the effectiveness of nematodes?

  • Follow label directions carefully
  • Apply at the proper pest stage and optimal soil temperatures
  • Thoroughly drench soil to reach where pests are active
  • Use proper spray equipment to avoid damaging nematodes
  • Reapply every 2-3 weeks until pest pressure subsides

Are beneficial nematodes compatible with other controls?

Yes, beneficial nematodes are fully compatible with most other organic pest controls, including horticultural oils and insecticidal soaps. Avoid applying chemical insecticides in conjunction with nematodes.


Beneficial nematodes offer gardeners, farmers, and landscapers a sustainable, eco-friendly method of controlling soil pests. These tiny parasitic roundworms are safe for people and the environment while providing effective, broad-spectrum pest suppression. When matched to target pests, applied properly, and used in conjunction with other organic controls, beneficial nematodes are a smart choice for managing insects in gardens, lawns, golf courses, and production agriculture. With a small investment and a bit of care, nematodes can work around the clock beneath the soil surface, reducing the need for chemical pesticides.