How to Breed Predatory Nematodes

Updated July 12, 2018

There are over 28,000 known species of nematodes, also known as roundworms. In fact, there may be as many as 1 million species on the planet. Nematode species are found all over the globe, from tropical to polar climates. Some can thrive in a saltwater environment, while others live in freshwater. Some species are helpful to the plants around them by attacking microscopic insects; these predatory nematodes are possible to breed if you're wanting to practice green gardening.

Add 2 or 3 gallons of water to a bucket. Then add compost to the bucket until the water level is only a couple of inches below the rim. Place an air pump from a fish tank into the bucket and turn it on.

Add 1/4 cup of liquid seaweed.

Pour in a handful or two of rock dust and 1/4 cup of sulphur-free molasses.

Let the mixture sit for a day or two. When you see foam forming around the edges of the bucket, you'll know that the nematode population from the compost has exploded in number. After you notice the foam, use the mixture within 3 hours to get the maximum benefit.

Spray the mixture onto the soil around the plant you want to help. Do not spray the nematodes directly onto the leaves.


The seaweed gives the nematodes the energy they need to multiply, and the molasses adds sugar which speeds the process up.


Applying nematodes during periods of direct sunlight actually kills many of the organisms. If the area is mostly shaded, you can apply at any time of day; if not, early morning or evening would be better than the middle of the day.

Things You'll Need

  • Compost
  • Rock dust
  • Molasses (sulphur-free)
  • Bucket
  • Liquid seaweed
  • Fish tank air pump
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