An Uncoventional Organic Method for Killing Root Knot Nematodes

An Uncoventional Organic Method for Killing Root Knot Nematodes

As you may have read in a previous post, root-knot nematodes recently became public enemy number one in the Hanbury House vegetable garden.  I was kind of depressed about it for a few days, struggling to find an Organic treatment to kill root knot nematodes in our garden.  Being a home gardener, especially an organic one, there are few options for dealing with nematodes in the soil.

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Organic Treatments for Root Knot Nematodes

Heat It Up

One of the most commonly recommended Organic methods to eliminate root-knot nematodes is solarizing the soil, covering the area with clear tearproof/ uv protective plastic for 6 weeks to allow the soil to reach 120 degrees for an extended period.  The area has to be in full sun for it to work.  However, soil solarization doesn’t just kill root-knot nematodes; it will also kill all beneficial nematodes, fungi, bacteria, and pretty much everything else alive in the top inches of the soil, good or bad. Heat and solarization are sort of nuclear options for treatment.

My particular veggie bed is only in full sun a few months out of the year, in the height of summer.  I am patient and could wait until then, but according to what I have read in some master gardening publications, solarizing is less effective near the coast where summer temperatures don’t get sufficiently high.  Our summertime highs are rarely over 80 or 85 degrees.  Great.  In all likelihood, it will not get hot enough to kill the little buggers in my coastal Southern California backyard, even in the height of summer.

Add More Nematodes?

Another option is to apply a commercially available product containing a type of predatory, beneficial nematode, Steinernema feltiae species.

Beneficial nematodes * are used by organic gardeners to combat a variety of garden pests, including root knot nematodes and beetle grubs in lawns. However, timing is important, and soil temperatures need to be above 60 degrees. Summer and fall are ideal seasons to apply them. In terms of products, there is no published research I could find by the University of California that lists this kind of product as effective.

Another Alternative

I need an effective organic treatment to kill root knot nematodes that works in the cooler seasons and in less than full sun situations.  A few of the management techniques recommended by UC ANR are better suited to a sunnier, more inland yard. After a bit of research and a suggestion from Patricia at the end of my other post, I decided I might as well give boiling water a try, especially since I will have to wait many months before trying solarizing.  In the past, I have managed to kill a few weeds with boiling water, and I am hoping it might also work against the root-knot nematodes in the garden. 

I came across a few university research papers that mention hot water above 120 degrees has been effective at eliminating nematodes on the root ends of bulbs, banana plant roots, hostas, and other greenhouse plant roots.  Hot water seems worth a shot.  Depending on the crop, the plant is left submerged for a different amount of time.  The publication about the banana plants said 30 seconds was sufficient to dip the ends of the plant and kill nematodes, but the one about bulbs said ten minutes.  I have no control over the time it takes to soak in, but if it starts out at boiling, by the time it cools down to 120, it should have had plenty of time to work and soak down in.  Boiling water is relatively cheap, non-toxic, and easily available, so the worst-case scenario would be it doesn’t kill the nematodes.

Vintage wedgewood 1094s stove white boiling water to kill nematodes organically
I was boiling two separate pots and a kettle of water at a time. I would carry each one out to the area in the vegetable garden and pour it on the soil in the area I found root knot nematodes.

I spent the better part of my day going back and forth between the back garden and the stove, dumping gallon after gallon of hot boiling water on the veggie bed.  At any given point, I had three different pots and kettles going.  Now the bed looks like warm steamy mud.  I plan to go back in a few days and top the area off with homemade compost to help reintroduce some beneficial bacteria and microbes. I sure hope it all helps, and I will report back in the comments in a few months on whether or not boiling water was an effective way to kill root-knot nematoads in the garden.  Wish me luck!

For more detailed information on Soil Solarization, visit UC Agriculture and Natural Resource about Soil Solarization for Gardens & Landscapes.

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23 thoughts on “An Uncoventional Organic Method for Killing Root Knot Nematodes

    1. I won the battle against the nematodes in the original area treated with boiling water, but I haven’t double-checked with a microscope. I added lots of compost before replanting anything because the hot water kills all the good microbes too. I have not replanted any highly susceptible plants in there. Now it grows irises, a multigrafted stone fruit tree, and herbs. I do grow tomatoes closeby and they have not shown any problems.

      BUT, the nematodes were probably in the original area for a little while before I realized it. Therefore, the nematodes were moved to a few other parts of my yard, probably unknowingly by my tools. I now sterilize my shovels every time after using them, just in case, and especially well if I come across a plant that looks infected, by pouring boiling water on them.

    2. Thank you. I had to use boiled water to kill the RKN after failed Neem oil treatments. But had to make sure the bottom of the pots was also drenched with almost boiling water. I basically had to kind of stir fry the soil in almost boiling water in small batches to make sure all soil was completely drenched.

  1. I would like to know whether this worked for you. I plan to use the same “scorched earth” method next time I come across nematodes. It’s the only solution available to home gardeners that can reliably kill all root-knot nematodes and egg masses in a short time.

    1. Hi Seun,

      I won the battle, but not the war against nematodes. In general, the boiling water method worked in that area, as far as I can tell. I haven’t double checked with a microscope. I added lots of compost before replanting anything.

      BUT, the nematodes were probably there for a little while before I realized it. Therefore, the nematodes were moved to a few other parts of my yard, probably unknowingly by my tools. I now sterilize my shovels every time after using them, just in case, and especially well if I come across a plant that looks infected, by pouring boiling water on them. Boy are they clean!

  2. Hi there, wondering how your boiling method worked long term? Our new rental has a serious root knot nematode problem.

  3. Hi, I’ve spent way too much time on your site, but so fascinating 🙂 Wish we could meet. I’m coming to LB for a Peace Initiative Meeting & Fair @ the convention center, 10/26, then off to my daughter’s new home in Anaheim to help w/ her garden. Found your site searching for good S CA plants (I’m from Bodega Bay, CA). My daughter (Nicki) also loves the vintage look & is new to gardening. I ‘spose what grows for you may not work in hot Anaheim but I’ll show Nicki your site for ideas:) I’m bringing her a sword fern to try in shady area, lavender, possibly nasturtium starts & an abutilon. Do you have any advice?

    1. Hi Karen,

      Thanks for the compliments on my blog.

      I grew up on the border of Anaheim, a few miles from Disneyland. Most parts of Anaheim have a similar climate to my neck of the woods. I am in Sunset zone 22 and a lot of Anaheim is as well. Some parts of Anaheim are in zone 23, which isn’t drastically different. I think your daughter will be successful with all those plants you mentioned.

      A good book about growing a garden locally is Southern California Organic Gardening by Pat Welsh. It is a month by month guide of what to plant and where. Another of my favorite local gardening books, that is out of print but can be found at, is called 52 Weeks In The California Garden by Robert Smaus. Both are a wealth of information on edibles and ornamentals that do really well in SoCal. Best wishes for your daughter in her new home and I hope you visit my blog again.

  4. I’m glad it helped, I’ll keep my fingers crossed for you. I also have a blog on wordpress and tried to follow you but for some reason it’s not coming up on my reader. If you have a chance, I would like to know the differences between Silkies and Cochins. I raise Silkies in my backyard garden, but find they’re somewhat delicate as far as health is concerned and was thinking of switching to Cochins.

    1. Thanks for the compliments on my stove. I love the stove, despite the fact it doesn’t have all the modern conveniences of convection or precise temp. It is actually my second vintage 1940s stove. When we used to live in a little duplex a few miles from here, we had one we bought from a friend for $40. We planned to bring it with us when we bought a house 3 years later, but this house still had its own original 1944 stove, plus it was bigger and had be recently serviced. We specifically requested it when we put in the offer on the house and later gave our first one to another friend.

    1. An update on Nematodes:
      Back in March, I planted 3 tomatoes in the bed that had nematodes and was treated with a deep soaking of boiling water. Only one of them is listed as being nematode resistant. So far, so good. None of the tomatoes are showing signs of infection from the little buggers. All are healthy and growing, but time will tell if the boiling was truly successful in eradicating the nematodes. I figure once the heat of summer kicks in or the tomato season ends and I remove them to see the roots, I will have a better idea if it worked or not.

  5. Lianne, you’re a smart cookie so I assume you’re already aware of this, but make sure that you don’t cross-contaminate other soil in your garden with the nematode soil by using garden tools/gloves/etc that could spread the little buggers around. After my solarization failed and marigolds made little to no dent, I decided to try VFN seeds, which are nematode resistant. Of course your variety is greatly limited, but at least it’s an option. I have a huge list of tomatoes that are resistant and even researched some pole beans that handle the nematodes well (Rattlesnake, Blue Marbut and Alabama #1).

    1. Thanks for the tips, Jessica! I appreciated that you shared all your own experience with nematodes on your blog, the bountiful backyard. I didn’t feel like I was alone in this battle and it gave me hope.

      Once I noticed the little buggers in on the carrots, I started being careful about sanitation of my gloves and tools used in there. Unfortunately, if they got out and around before that from my stuff, there is nothing I can do but wait and see where the turn up. I am optimistic since I have not seen any damage or signs of them elsewhere that they were pretty isolated in there. I am also keeping my fingers crossed that the boiling water may have helped. I even dumped my giant pot of left over boiling water from my strawberry kiwi jam canning in there when I was done.

      In the past, I have always made sure to get tomato varieties with a “T” in the their disease resistance coding since my hubby mistakenly introduced tobacco mosaic virus in that part of the yard, almost 15 years ago. He made some crazy homemade plant “tonic” recommended by Jerry Baker, a self proclaimed master gardener, who once had shows on PBS. It was called tobacco tea. Bad idea. I haven’t seen any signs of the disease for 10 years, knock on wood. Anyway, I appreciate the tips and will look for tomatoes and beans that also have N in the disease resistance code. Thanks!

  6. Have you tried marigolds? Look into it. They need to be grown for at least 2 months fairly dense and then turned into the soil for best protection. Of course this leds to more marigolds if you don’t dead head…but it gets rid of nematodes… and looks nice. Don’t fall for the gimmicks either all of the marigolds work some jsut work better than others so go with what is cheap and easy to deadhead.

    1. Thanks for the suggestion Barbie. I will probably try that once the weather warms up enough to sow marigolds.

    1. Thanks, I hope it works too and that it is not an increasing issue. I have seen a lot of SoCal posts from other garden bloggers having similar issues with root knot nematodes in the last couple of years. I am not sure if I have been lucky all these years and root knot nematodes are actually common in southern California, or if one of the tomatoes or peppers I brought last Spring introduced them into the raised bed. The one carrot is all I have seen nematode nodules on, so I am hopeful I will get them eliminated.

      1. In the Santa Clara Unified School District Adult Ed Teaching Garden, we are using crab meal to some success. 10 lbs. per 50 sq. feet, dug into the bed. Then going forward, we are using spent coffee grounds as a 3 – 4 inch mulch: caffeine kills some insects. After knocking down the population, the grounds seem to fertilize and make it less hospitable to the root knot nematodes..

I would love to know what you think about this.

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