How to Get Rid of Root-knot Nematodes

Root-knot nematodes in the vegetable garden

My tomato plants and green beans were struggling. I’m an avid organic gardener, carefully enriching my soil and tending my plants, so this was a real puzzle. My pride was wounded. It took me a couple of years to admit that something was wrong with my soil. Turns out that the culprit was root-knot nematodes. I’m going to tell you how to get rid of those nasty root-knot nematodes.  

The effect of nematodes 

The tomato plants were spindly and the leaves turned yellow no matter how well I fertilized them. The rows of green beans did not grow nearly as lush as they had in the past. In fact, it seemed to be all they could do to give me a few green beans per bush. I’ve always said that beginner gardeners can’t go wrong with green beans. They are easy to grow and the yield is amazing. If green beans are so easy, then why were my green bean plants so poor these past couple of years?

Admit there is a problem in the soil

After about three years of expecting a great harvest and getting less every year, I had to find out what was wrong. I don’t know why I couldn’t face the fact that I had a soil problem. In the past, when the leaves would start getting yellow or spotted, I would sprinkle them with sulfur dust and they would recover and keep on growing their beautiful, lush bush with beans hiding under the leaves. But that wasn’t working anymore. 

I had to admit that, even though I was diligent to enrich my soil organically, the problem was progressively getting worse. After I let go of the denial that anything could be wrong with my well-tended soil, I went to work to fight against root-knot nematodes. 

What do nematodes look like? 

They are so small that you can’t actually see them. But you can see what they do to plant roots. When I pulled the green beans and the tomatoes up, it was very evident that the roots had bumps on them. For the first couple of years of seeing the lumps on the bean roots, I thought that was normal. I thought it must be the nitrogen nodules that legumes have on thier roots. But as the years went by, those “knots” got bigger and bigger and the plants got yellower and smaller. 

When I saw them on the tomato roots too, I had to admit that those knots were not good. Those knots were evidence of a “bug” that was too small for me to fight. 

For a technical explanation of them and more images, read about it in this article by Backyard Gardener, University of Arizona.

Root knot as seen in the roots of a plant.
microscopic nematode roundworm
A "zillion" of these teenly little roundworms cause a lot of damage to your vegetable garden.
this is what infected roots look like

An organic solution to rid soil of root-knot nematodes

I learned that marigolds will get rid of root-knot nematodes in your garden soil. But, how can growing marigolds affect the soil? They are a pretty bush with pretty flowers. What if interplanting them in the garden solved my problem? It was an easy solution, so the choice was clear. Plant marigolds!

How to plant marigolds

Two options

Sow directly into your garden soil. Marigold seeds are small and small seeds need only a small amount of soil to cover them. The easiest way to sow small seeds is to scatter them onto the soil and then “sprinkle” or “flick” loose soil over the top of them. It’s tempting to bury them too deep, so be careful. You only need a little bit of soil over the top, but they also must be fully covered. I sowed so many that first year that I scattered them and then stirred them into the soil with a garden rake. I knew there would be a loss of germination, but I hoped it would be ok. It was. Never let the soil completely dry out, but don’t drown the little seeds. They need to breathe in-between watering. 

Sow them into containers

When direct sowing is not an option due to hard freeze or simply for convenience, start your plants in a container. My favorite way to start small seeds is in seed trays filled with “seed-starting” soil. The light soil is very important if you choose this method. You may need to water more than once a day since the soil is very light and does not hold water for long. Be diligent to check the soil. Damp is ok, dry means that you need to sprinkle them with water until the soil is moist. 

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How many marigold plants do I need in order to get rid of root-knot nematodes? 

I wanted the soil to be cured so badly that I sowed a ton of marigold seeds and got a ton of plants to transfer throughout the garden. I had no idea how big they could grow. Those marigolds grew and grew. I didn’t mind. They are pretty and they have a fresh, clean scent that is noticeable when you walk by them and more so if you brush up against them. They grew so big that they actually began to take over the tomato plants that I interplanted them with. The tomatoes didn’t seem to mind, but I had to work around the marigolds to pick tomatoes! 

You can see them here, interplanted with the tomatoes. This photo is from 2020 and it is now one year later.

marigolds interplanted with tomatoes
Healthy green bean plants a few days before the first beans are ready.

Lo and behold, the green bean plants improved too, that very first season. They weren’t quite as tall and full as I had seen in the past, but that part had to wait for the next season. Here is a photo of my bed of green beans the following year, 2021. So healthy and full of blooms and green beans.

But, in my excitement to share the good news, I got ahead of myself!

By the end of the season (my zone has a Spring garden that is finished by mid-June) and after I pulled the spent vegetable bushes and stalks up, I had a garden full of large marigold plants. All over the garden!

How long do I let marigolds grow in the garden?

What was I to do? I decided to leave them in the ground and let them grow through the summer until I needed the space for my Fall and Winter garden. My Fall garden is only about one-fourth the size of my Spring garden, so I left many marigolds to continue to grow until they died. Some of the plants spread out to six feet wide! As they grow, the limbs touch the soil and root themselves and keep on growing. 

Finally, when Winter was truly upon this mild Florida climate, I pulled what was left of them (dried bushes) and made a pile of just marigold mulch to use in the upcoming Spring garden. 

Incorporate the dried marigold bushes into your soil

Before Spring planting time, when I prepared the beds for tomatoes and green beans, I gathered the dried marigold bushes and incorporated them into the soil. I turn the soil in my vegetable beds every year, adding the appropriate natural amendments that that particular vegetable plant needs. That is when you add the dried marigold bushes. 

To learn about how to prepare your garden beds, read How to Prepare Your Soil for Your Spring Garden

For just a little

A garden journal is exactly what you need to keep track of what worked and what didn’t. All this is done for you! For just a little, you can get a printable document that’s got you covered from your seed wish list to your harvest records. There are 39 pages of charts, record keeping, garden map grids, and lots of pages for your garden journaling about the garden in general as well as the individual veggies and fruit that you are growing. It’s only $4.99! You can find out more details and order it here and get started right away. (A digital version is also available in the shop.)

How do dried marigold bushes affect green beans and tomatoes? 

dried marigold in bottom of garden bed

It is now mid-April of 2021, the following year after planting a ton of marigolds. The green beans are knee-high and lush and full of blooms and little green beans that will be ready to pick in just a few days. The tomatoes are healthy, the vines are bushy and full of blooms and the first tomatoes are forming on the vines. This little old farmer woman has a full heart too! 

healthy green bean plants blooming

A bonus that happened is that the marigold plants “self sowed”. I did not have to start the seeds this year. They came up all over the garden in random spots. I transplanted them randomly throughout the garden. I don’t need as many as I planted last year, but I think I will always have a few in my garden. 

How to get more green beans

I found out how to extend a green bean harvest last year. The bed i was growing beans in last year was in the full sun all day long. This year, they have partial shade for part of the day. I will have to see how that works. I may still need to do what I wrote about in THIS POST

Plant those marigolds! Now that you know what will get rid of your root-knot nematodes, plant them asap! You’ll be glad you did.

“But seek first the kingdom of God and his righteousness, and all these things will be provided for you.Mat 6:33 CSB

A photo of the author, Deborah Schreffler

Debbie Schreffler

Veteran Homeschooler, avid gardener, and proud grandma

I believe that you can design a peaceful lifestyle while you homeschool, complete with a garden if you want, and meals that will make the best memories you ever could imagine!

I homeschooled seven kids through high school, starting them all with a lot of planned, hands-on activities. Then, I centered subjects around the activities. That gave them lots of room for their natural curiosity to be satisfied as they learned about God’s world.

Let me help you teach kids, grow food, and stay calm!

pin for root knot nematode


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