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Golden Guardian marigolds reduce root-knot nematodes

Harvesting Seeds: Nematicidal Marigolds

As you pull out your tomato plants this fall, check the roots for galls. These are lumpy swellings that indicate that you might have nematodes living in your soil that are stunting the tomato plant’s growth.  (You can learn more about it from our Got Nematodes podcast)

We had that problem last year so we planted Golden Guardian Marigolds, the roots of which contain a toxin that kills harmful nematodes.  Now it’s time to harvest the seeds and turn the crop under so it can do its job.


Golden Guardian marigolds are nematicidal.  By growing them for at least 3 months,
then chopping up the plants and digging them under, the marigolds supposedly kill
off nematodes and their eggs.

Another benefit of growing marigolds is that you’ll never have to buy seeds again.  In fact, you may never need to plant them again, since they re-seed themselves so easily.  Just in case, we’re saving seeds.


Marigold seed heads. Each thread poking out the top is a seed

To harvest, you can cut off the spent seed heads, or lay out a tarp and thresh the entire plant against the tarp.  Some seeds come loose this way, but we found that we needed to help by hand a little.


Marigold seeds and chaff.  The threshing method creates a
significant amount of chaff, as
opposed to the seed head method


After threshing and winnowing (or picking the seed bundles out of the heads)
you have finished seed.

We will plant these in the area of the garden where the tomatoes had galls.  If you are interested in growing nematicidal marigolds in your garden, you’ll find Golden Guardian at Park’s Seeds. At the time of this writing, they are currently sold out, but check back to see if their supply has been replenished.

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