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So after pulling this springs planting of carrots, apparently the soil has an abundance of root knot nematodes--considering all the balls and lumps that formed at the ends of my stunted, forked, hairy carrots. also explains why my radishes are probably not swelling up, but instead just stagnated and now starting to go to bolt with the introduction of the summer heat. Possibly even the reason for my strong tasting lettuce plants. I have a few french marigold plants in there now, as ive heard their chemicals will kill off nematodes as they attempt to feed from it. And put down some seed for a lot more french marigolds while we are in the summer months to help out even further. My question is if there is anything i can apply to the soil itself to help speed up this process of displacing this army of microscopic root munchers?
I think they are more prevalent in sandy soils with low levels or organic matter.
If so, I would incorporate LOTS and LOTS of different kinds of organic matter. It will decompose over time, and help out the soil.
Soft green things like lawn clippings young leaves of weeds or prunings and kitchen things like vegetable trimmings and fruit parings will decompose very fast, and the green leafy stuff adds nitrogen.
Dried brown things like fallen leaves will decompose fairly fast in the warm months when blended with the green matter, or will decompose slower over the winter.
Harder to decompose things like sawdust will last longer.
Most manures will add some nutrients, but some are rather low in nutrients, and if you add them with the other things (sawdust that was used for animal bedding, for example) the nutrients will go to support the decomposer organisms. This is fine.
When you are ready to plant again I would add organic sources of fertilizers such as blood meal, bone meal, fish emulsion and similar materials according to the needs of the plants.
Other ways to help include solarization, crop rotation and planting resistant varieties.
Rototill, get rid of plants and leave the soil loose and level. Water it.
Cover with clear plastic and seal the edges, for example by shoveling soil around the edges.
Let it heat up in the summer sun for several weeks.
This will kill the nematodes in the top area of the soil so you ought to be able to get a good crop before the soil is invaded again.
There may be harsher ways to kill them, but they will come back even if you use more toxic methods.
Organic matter is very helpful to clay soil, too.
As the organic matter breaks down to very fine particles the clay particles cling to it making miniature clumps that are fantastic to garden with. It takes years to work up to that good a texture of soil.
Any you must never walk on this type of soil.
Lay out the garden beds, add sides if you want (I use 2 x 6 lumber) and always walk on the paths.
Stepping on clay soil breaks down the connections between the organic matter and the clay and the soil becomes all the worst things you have ever heard about clay.
Treat it right and it is rich, fertile, holds water very well, yet has reasonable drainage for most plants.
oh yeah i know quite well how nasty the stuff can be. and for that reason i designated trails through there that i can walk through and reach all that i need to work with without having to set foot in the actual growing spaces. in this shot i had layered a good inch or so of potting mix onto the top of the soil (so the sun wont bake the clay so solid so easily.) to add to said organic materials, and to help hold moisture a bit. still plenty of leftover lettuce and carrots left in there as you can see. tomatoes in the very back of the photo, peppers in the middle, and a place dedicated to just flowers. (to draw in the pollinators)
i did think ahead though with said clay soil, suspecting that it may not work out the best for carrots considering the very fact that it is clay soil with this just being the second gardening year that i have worked in this space (it did get one nice application of compost last year).
So i took it upon myself to sow some "Little fingers" carrot seed in a 2.5Ft wide x 3Ft deep container of potting mix, and those turned out excellent!
We plant shorter carrots like short and sweet in a raised bed. I find the little fingers too small.
Also I just read a gardening article where they talked about putting a trench filled with potting soil through the clay soil and then planting the carrots seeds on top of the trench. They said they are able to grow the bigger carrots that way. I plan on trying this method in for fall carrots.
You might want to verify with your County Extension Agency, or a knowledgable nursery that you actually have RNNs. My soil is really hard and it is difficult to grow root crops.
Do you have any idea where they may have come from? My garden got infected by them when some left over construction sand was added, yes, they like sandy soil. It took a couple of years of adding a bunch of Organic Material to get rid of them but they didn't "like" living here. The environment wasn't right. But if you didnt have them before they had to come from some where.
i gave it that assumption based on photos i see online of carrots that are infested with them. these are about how most of mine look, they definitely have the random little balls down on the ends of the fibrous roots:
i read somewhere that nematodes are also attracted to tomatoes, and i did in fact grow tomatoes in the same spot that the carrots are this year (of course i found that little tidbit of info out long after the carrots were off and growing, lol)
before i was given this garden bed from my mom, she used to use it solely as a rose bed, but she never really did any upkeep with it, she especially let things go regarding the weeds. basically a "let it fend for itself" type method, lol. i really havent the slightest idea how the nematodes would have come around (if that really is what they are) unless it could be that the nematodes were just always there and decided to show themselves once i attempted root crops.
You haven't noticed any problems with roots on other plants, like your tomatoes? RNNs nematodes thrive in sandy soil and from my experience they injure the roots on all plants, not just root crops. I remember my cuke roots were really bad.
If your other crops are doing OK, then let them grow.
Any that show signs of being unthrifty, or die, dig them up and examine the roots. On legumes (peas, beans) look at pictures of the beneficial organisms that colonize these roots so you know the difference.
As noted above, the nematodes do indeed have to come from somewhere. But that could be something as simple as a shared plant from an infested garden, using tools without cleaning off the mud, or even walking from an infested area to the 'clean' area without removing the mud from your shoes.
Good that you already know how to handle the clay soil! Keep on adding LOTS of organic matter every year.