Nematodes or New Grass Seeds, Which Goes First?


Last fall we moved into a house that had been uninhabited for 10+ years. As you can imagine, its been a struggle to wrestle the house and grounds back from nature (mice, birds, cockroaches, ants, fleas, squirrels, etc). The 3000 SF backyard was largely decimated by the renovation crew and what is left is a mix of gravelly rocks, hard soil and a thin top layer of weeds. Our landlord has agreed to provide us with grass seeds and straw, which we were about to put down when we found out our foster puppy has tapeworms (yuck!). Although neither the puppy, nor our own dog show signs of fleas, we are told this tapeworm comes from fleas. (Double yuck!). I’ve ordered 30 million nematodes to “naturally” combat the problem, but don’t know in which order I should proceed? And how long I should wait between treatments? Or, alternatively, might the nematodes and grass seeds be put down together. We live in the American South, Chattanooga, Tennessee to be exact. Current temperatures are between 35*F overnight to 75*F in the day. Until the Sweet Gum Tree (aka tree from hell that drops spike balls everywhere) gets its leaves back, the yard is almost entirely in the sun. The kind of nematodes I ordered are: heterorhabditis bacteriophora, steinernema carpocapsae and steinernema feltiae. Any other advice on how to grown a pretty lawn is most welcome. We moved from an apartment in San Francisco and know next to nothing about gardening. Thank you so much for taking the time to read and respond. We will be hanging on your every word.


Steinernema feltiae, Steinernema carpocapsae and Heterorhabditis bacteriophora are three species of what are termed “beneficial nematodes” used for the biological control of soil insect pests.  While lethal to several different types of soil-dwelling insects, beneficial nematodes are completely harmless to plants, animals and humans, and are an effective and safe alternative to chemical pesticides. 

The three species of nematodes that you have ordered live in different layers of the soil and attack different groups of insect pests.  Heterorhabditis bacteriophora (Hb) live at about 3 to 17 cm (1 to 7 inches) from the surface and prey upon slow moving larvae such as grubs (the larvae various types of beetle species) and termites, including the larvae of fleas.  Steinernema feltiae (Sf) and Steinernema carpocapsae (Sc) hunt closer to the surface, within the top 7cm (3 inches) of the soil, and attack larvae, pupae and adults of various types of insects.  Sc will also attack the adult fleas you are trying to eliminate.  Nematodes enter the host and kill it from within by infecting it with a bacterium that is harmless to the nematode, but deadly to the host.

Nematodes can be applied anytime but should typically be timed with the lifecycle of the target pest and soil temperatures.  Optimal soil temperatures vary for each species of beneficial nematode, but generally fall within about 20C to 28C (70F to 83F), so application is typically done in the spring and autumn.

Since you’ve already ordered your beneficial nematodes, I think the timing of your application is going to be a bit of a challenge if you also want to seed a lawn this spring. Nematodes have a limited “shelf life” in their transportation containers.  Most suppliers recommend that the nematodes be applied within two weeks of receipt.  Before application, nematodes should be stored a fridge.   Most suppliers recommend two applications about 7 to 10 days apart. Check with your suppliers’ specific recommendations for storage, viability and application.

The challenge you have will be aligning the timing of the optimal application conditions for the nematodes and preparing your yard for the optimal conditions for seeding a new lawn.   From your question, it seems like the nights in Chattanooga are still quite cool, so you will need to wait until your soil has reached the optimal temperature range described above.  Hopefully, your nematodes will still be viable by this point. 

The other challenge will be preparing your yard for seeding.  It sounds like the renovation process has really degraded the conditions in your yard for a healthy lawn.  Since the ground is hard and compact, you will want to loosen the soil to ensure the right conditions for root growth and drainage.  You can do this by hand with a shovel or pitchfork, but given the size of your yard, you may want to consider renting a rototiller.   Next, you will likely need to amend your soil with about a 5cm to 8cm (2 to 3 inches) of a top-soil rich in organic material.  You can contact a local gardening centre or landscaping company to have the soil delivered and applied.  Once you have a healthy base for the lawn, you can apply grass seed following supplier’s recommendations for application methods, rates and fertilization.  Contact a reputable local garden centre for recommendation on a seed mix appropriate for your growing conditions.  The optimal temperatures for planting grass will depend on the specific species you choose, but many grasses germinate best when the air temperature is between about 15C and 24C (60F to 70F). 

Once seed is applied, lightly rake to cover the seed with a thin layer of soil, but don’t over do it.  You want to lightly cover the seed with soil to help with germination and protect from birds, but you don’t want to bury too deeply.  As you planned, you can mulch your newly seeded lawn with straw to help retain moisture and protect it from birds and other pests.   You will need to keep the soil moist at all times. The tender grass shoots will quickly dry out and die if not kept moist.

Ideally, you would want to apply the nematodes after your yard is prepared for the lawn, as the process of rototilling and amending the soil will seriously disrupt their environment.  Our Master Gardener chapter is based in Toronto, Canada, so I am not familiar with the seasons in Tennessee and how quickly temperatures will warm up to the optimal conditions for both the nematodes and for germinating grass.  I think your best approach is to prepare your yard for the lawn, and then apply the nematodes.  Hopefully, they will still be viable at the point when the soil reaches the optimal temperature.  You may need to re-0rder a supply of nematodes and apply again a little later in the spring, or in the early fall.

The Tennesse Master Gardeners  may be able to give you specific information for your area

Sounds like you have a challenging, but exciting project ahead.  I am sure the results will be terrific!