Myths vs Facts: Marigolds and Root Knot Nematodes

Do you use marigolds to control nematodes? If you know for a fact that what you're doing is working, keep doing it! Otherwise, if you're like me, you've been frustrated by contradictory info on the net, and even from people who sound like they know what they're talking about! Here's a study from the University of Florida sheds light on why there's so much confusion. Did you know that "not all marigold varieties control all types of nematodes"? Did you know some marigolds actually HOST some nematodes? So if you don't know what you're doing you could make the problem worse! YIKES!

Unless you plan to get your soil tested to learn which species of nematodes you're dealing with, you might be safe using French marigolds (T. patula) which are know to be the most effective against the widest range of nematodes.

University of Florida IFAS Extension Report:
http://edis.ifas.ufl.edu/ng045

Thanks for that useful link!! 


Did you all know some nematodes are beneficial?
http://www.dirtdoctor.com/Beneficial-Nematodes_vq2139.htm

I did know that some nematodes are beneficial. In fact, you can buy them to add to your garden.

Life is confusing!

I'm off to read the links you two posted.

And, by the way, Dstack, really good public service announcement - thank you!

camprn wrote:Thanks for that useful link!! 


Did you all know some nematodes are beneficial?
http://www.dirtdoctor.com/Beneficial-Nematodes_vq2139.htm

That's also good to know, but I wish there were beneficials that would destroy the root knot nematodes. I was told by a company that sells beneficials that they're working to engineer beneficials to do so. Yikes!  I have a huge problem with GMOs!

Shaking head in dismay. The world is confusing and often scary.

I think I recall reading that African marigolds leave a residue in the soil so strong they can inhibit other plants from sprouting.

Marc Iverson wrote:I think I recall reading that African marigolds leave a residue in the soil so strong they can inhibit other plants from sprouting.

I've read that about French marigolds and bean plants. One place I saw this was.... 
http://www.ghorganics.com/page2.html

dstack wrote:

Marc Iverson wrote:I think I recall reading that African marigolds leave a residue in the soil so strong they can inhibit other plants from sprouting.

I've read that about French marigolds and bean plants. One place I saw this was.... 
http://www.ghorganics.com/page2.html

Nice link! I love reading about companion plants, though I've grown more skeptical of claims about many of them. Partly for the same reason I love reading about them -- every other chart or web page or write-up of them tells me something contradictory!

I made a hard copy for my binder.  I'm still trying to lay out my spring garden.  My seedlings under the lights are popping up so I'm getting closer.  We are having some rain    with a little freeze this week.  Maybe even some rain next week.

I've read so many articles touting Borage, and I'm happy to report that my seedlings are looking good so far.

Oh, you started them already? Cool!

I spoke with someone at my Master Gardener's class who grows borage and says it grows great around here, real quick and the bees love it, and it self-seeds readily. Woo hoo!

Keep us up to date on your borage progress -- I remember a few people got in on the borage-talking and said they wanted to try it out this year.

I hadn't planned on starting to grow them yet, or maybe indoors at all ... anyway it was so far off that it didn't matter what I remembered. Then again, you live in Cali and where I live, it's supposed to be 20 degrees on Saturday.

I'll see if I can post a photo tomorrow (if I remember)!

Borage babies

It's always exciting to see the seedlings pop up. I've got to make some tough decisions about getting rid of some things to make room for my Spring garden. I'm also adding quite a bit of mushroom compost to the MM. I used up my last batch of home made for my papaya plants.

My Spring seedlings have also sprouted. I started them in those biodegradable egg cartons, then transplanted them into little pots of nothing but mushroom compost, until I can make room.

Bees love borage and the flowers are delicious!

Ha!  A new myth / fact to challenge!!  I sure hope the bees are attracted, all 10 of them.

Borage: to bee, or not to bee

dstack wrote:I've read that about French marigolds and bean plants. One place I saw this was.... 
http://www.ghorganics.com/page2.html

Dstack, I read the university article you cited with much interest.  I planted French marigolds last season and they exploded with vibrant orange petalsl with red tips.  I'm not sure if they helped, but I did not really have any pest problems other than aphids, white flies and dreaded horn worms.  Also, last season, I too read the ghorganics article and I had some success following the advice there.  Thanks very much for your posts!

martha wrote:Bees love borage and the flowers are delicious!

How do you like the leaves and/or stems? I've never eaten any of it before, and was thinking I might grow it as an actual leaf crop for regular eating, if the taste is good.

sanderson, with all the flowers we've been talking about planting, if we don't finally attract bees, I think we'll just have to buy some!

I'm hoping for us!!

Marc Iverson wrote:sanderson, with all the flowers we've been talking about planting, if we don't finally attract bees, I think we'll just have to buy some!

This is a reality. Pollinators are in trouble and decline everywhere.  If you aren't seeing bees when you have a lot of flowers, you may be in an area with few bees to attract.

If you have an interest in beekeeping head on over to the keeping bees thread. Also if you want to start keeping bees this season, get on the project soon because the bee packages tend to sell out quickly, usually before the end of February.

I did notice that in my garden the marigolds did attract many types of insect. I don't know that I have root knot nematodes, so I cannot really speak to that point. But the marigolds sure are pretty.

I planted so many dwarf French marigolds in my vegetable garden they grew and grew and I had to remove about half of them.  I transplanted them to a border near the house so everybody could enjoy them.  I cut them back sometime during the growing season and they kept growing up until the first freeze.


Thanks to pollinator for the seeds.

yolos wrote:


Thanks to pollinator for the seeds.

That's so awesome!   

That's really pretty, Yolos!

How did you cut them back? I deadhead mine religiously, but it sounds like you took a stern approach to the greenery too.

Marc Iverson wrote:That's really pretty, Yolos!  

How did you cut them back?  I deadhead mine religiously, but it sounds like you took a stern approach to the greenery too.

The tall ones in the back row next to the fence were not cut back.  The ones in the front were so big and tall that the branches kept falling over into the grassy area and we could not mow around them.  So I just started cutting them back where ever they looked like the branches were falling over.  At one point, the plants in the front row were cut back so that there were no flowers on the plants at all.  When I cut them back, I tried to leave the shorter branches that still had buds and cut the longer branches that were falling over due to their length and heaviness due to all the flowers.

Yolos, Show Place! Or should I say, Best in Show.