What's the word for


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plants that release chemicals into the soil that prevent other seeds from germination?

Last summer I had a lot of seeds (direct sown) that never germinated. I noticed that it seemed particularly bad near cabbage garlic and onions. Well and my carrots did extremely poorly around the spinach. 3 packs of seeds netted about 2 dozen carrots.

I was planning on moving my allium patch to get it fresh soil and tilling in the old patch but now I'm worried about contaminating the rest of the garden. I'm still trying to get a handle on crop rotation and companion planting.
 
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A lot of people use the word, "Allelopathy" in a negative connotation; however, the allelopathic effects can either be negative or positive. Just my PSA for the day:)


Excerpt:

Allelopathy refers to the beneficial or harmful effects of one plant on another plant, both crop and weed species, from the release of biochemicals, known as allelochemicals, from plant parts by leaching, root exudation, volatilization, residue decomposition, and other processes in both natural and agricultural systems.
 
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I thought it was allopathic and found lots of information about herbal medicine.

Spelling counts I guess.

Ok, off to do research.
 
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Well I found out a fair bit about allelopathy but not the specific information I was hoping for. Time to ask the folks with experience.

How long do these chemicals tend to stay in the soil?

While my onions are basically in one sequestered patch, I do have cabbage spread throughout the garden. And a few garlic bulbs in various places. I'm debating on transplanting all this to the one plot for now so the rest of the soil can air out .

This still leaves the problem of what to do with the current allium patch, which will end up overcrowded, and still has soil needing refreshment and loosening (it's getting compacted)

Id like to move the allium to a different location with fresher looser soil in the spring, same for the cabbage.

Next question, since my situation seems to mostly affect direct seeding and germination, would starting the plants indoors and transplanting be the way to go? Or do the onion and cabbage toxins affect the plants as well (note, I'm planning on friendly combinations of plants, not seeds). Basically, instead of direct sow, if I start beet seedlings would they be ok in the previous allium patch? They are supposed to be good companions.
 
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I would imagine not too long, since these compounds have been around for eons, nature knows pretty well how to break them down quickly. Even if it were a much bigger system, say a freshly cut down Black walnut tree, the soil could be remediated in a matter of weeks.

If you go the route of remediating with manure (including composted manure) and mulch products such as, straw, hay, cut grass clippings, you want to be careful not to use products contaminated with various persistent herbicides. You can not know if these things are contaminated by looking.

These herbicides are Picloram, Clopyralid and Aminopyralid. The various trade names are listed in my link below. These synthetic compounds can remain in the soil and will negatively affect various broadleaf plants for at least a year and reportedly longer.

Here's some more information so that you're aware of this danger.



There's a lot of videos on youtube where people have had this problem, here's just one example.

 
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Herbicides aren't the concern, this is stuff already in the garden. I don't use fertilizer as a general rule.

I'm worried about what's coming from allium and brassica plants. This garden is pretty organic, mainly because I can get organic materials for free.

But that doesn't address the allelophactic problem I seem to be having. It's good to know that the effects don't last much more than a couple weeks. I can probably pull the garlic, onion and cabbage, put them in a container for a couple weeks and then replant
 
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I've never had issues with these plants contaminating soil, I do grow various allium and brassica plants, but I guess not the same variety as you. As I said before, these compounds, whatever they are, are found in nature, so it won't take much time, but it depends on some factors, such as how bio-active you soil is, how much water the soil receives...

To remediate the soil all you need to do to speed up the process is to apply compost and mulch over (that's what I would do), but the most important thing is to plant something that will grow, because it takes plants to make soil healthy; plants feed the soil organisms that will remediate your soil.

How much area are you trying to remediate and How long ago did you remove the plants?


P.S. My only point about herbicides is that if you do compost/mulch, be careful where you source it if you get it from outside sources.
 
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I was getting manure every other year and ended up with a chickweed infestation, so now I'm sourcing grass clipping from the yard and dead leaves from a wooded area near home.

I can get things to grow at the beginning of the season, it's reseeding that has posed a problem. Though when reseeding I was trying to plant something different in those locations. I'm still awaiting the last frost, probably start tilling in a couple weeks and planting late May.

Would I be better off planting the same crop as was picked? It makes sense that say beets wouldn't be toxic to beet seeds.

FWIW, I tend to be a direct sow kind of guy, I do buy tomatoes, pickles and a couple other things as plants due to the fairly short growing season. I don't like starting seeds in the house for a few reasons, space and our energy efficient windows being the worst.
 

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