Breeding for resistance to allelopathy in a "milpa"

After @julia.dakin suggested that I could grow peppers “milpa-style” under taller plants instead of under rowcover, I’ve been giving this idea a lot of thought.

Denver, Colorado may have late and early frosts, cool nights, intense heat, drying winds, and lots of hail—but it does have one thing going for it: lots and lots of intense sun. We have a missing mile of atmosphere, and many fewer cloudy days than many other places; as a result, most plants can get by with a bit of shade here. So there would be less competition for light than in cloudier climates. There would still be competition for water and nutrients, but as I’ve posted elsewhere, I’m gardening intensively on a quarter acre lot; I can certainly supply more water to a multi-storied planting. Maybe this is the solution to my perceived need for rowcovers for hail and wind protection for a wide range of crops! And with landrace growing, my plants would get better every year at competing with the overstory.

Architecturally, the annual plant that would work best for my overstory would be giant sunflowers. They could be pruned up to provide understory room; they are native here, and shrug off Colorado’s wild weather. In fact, I have to weed out volunteer sunflowers to keep them from totally taking over. (They wouldn’t provide much cover in the early spring, but that might actually be an advantage; it would allow the crops to get established. And I’m not averse to covering small pepper or eggplant or cucumber seedlings with cardboard boxes on cold nights—as I explained elsewhere, while I want to get away from purchased inputs, my urban garden will always be somewhat intensive to maximize the use of space.) Also, we eat a lot of sunflower seeds. They are too low value to grow in my home garden, but if they were sheltering other crops they would work.

The big problem is that sunflowers are allelopathic; they tend to suppress the growth of nearby plants. This effect can be minimized by removing the sunflower debris, but it is still there.

Could plants be bred to resist this allelopathy? And if allelopathy can be easily overcome by evolution, why hasn’t it ceased to exist in the wild? (Drawing on our discussion of the book Darwinian Agriculture.) I imagine I’d want to also select for sunflowers that suppress my crops the least, or I’d be suffering from just the sort of “arms race” that Denison describes in that book.

Or, of course, I could just “hedge my bets” by planting some of each crop under an overstory, accepting lower yields, but realizing that in a bad hail year, only the protected plants would produce at all.

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That’s an interesting idea. We garden at 1000m (~3300ft) and UV can be a bit intense. Peppers need shade here to do well. This season we grew them just east of some robust bush beans which provided afternoon shade. The peppers did well enough but stayed quite small, unwilling, it seemed, to venture too far from beneath the bean canopy. We also grew grain amaranth elsewhere and I’m thinking this would be an excellent companion for peppers - amaranth and peppers down the centre of the bed and bush beans or a similar legume on either side.

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I’m at 5300 feet, and the radiation is intense! That’s interesting about your experience with keeping the peppers in the shade. I’m wondering how much of the benefit of the rowcover comes not so much from warmer temperatures as from filtered light.

I was thinking about using amaranth as the overstory; we grow some anyway. But I was thinking that each amaranth plant wouldn’t shade as much area as a sunflower, so they’d have to be planted closer together. The amaranths I grow produce a tall, fairly narrow column of vegetation.

Maybe I could plant the amaranths, prune off side shoots up to about three feet or so, and then top them, which would make them produce a spreading bush of side shoots at the top. Of course, that would be more work, and would likely not end up getting done.

Growing a shorter plant along the sides is a good idea, since it would provide some more shade.

Sounds like a good idea to me. We also are transitioning to milpa growing as our go-to after growing three sisters for the first time last season.

I think the answer to the first question is yes until proven otherwise. We have a lot of mature black walnut on our place and I feel like I may have seen things growing fairly close that are on the juglone-sensitive list.

An answer to the second question is more involved, but there is probably nothing easy about it. It might be relatively easy for a plant to gain advantage over its peers by being slightly more juglone tolerant. But with no steward guiding the selection of this trait and a huge non-juglone containing ecosystem in which to live and reproduce, it’s unlikely this trait would cause such dramatically better reproductive success as to become firmly established. And in the unlikely event that it did, there’s still all the other juglone-sensitive plants. And if somehow such a large subset plants naturally become juglone-tolerant that it began to encroach on black walnuts, now black walnuts that produce more juglone, or juglone together with another allelopathic chemical, might enjoy greater reproductive success than their peers.

So while I’m confident allelopathic resistance is breedable, I doubt it would be possible for it to arise naturally, firmly, and generally in the wild to the extent that the strategy of producing allelopathic chemicals is rendered ineffective.

I think @Joseph_Lofthouse has had good luck intercropping pole beans with sunflowers.. We might buy trying sunflowers in a milpa this year and can let you know how it goes for us :slightly_smiling_face: let us know how you go!

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I’ve also grown beans with sunflowers for about 10 years with no problem. Whatever allelopathy sunflowers have, it doesn’t extend to beans. I’ve also grown them with radicchio once or twice. I don’t know about peppers, though.


Either that or it takes a lot of sunflowers growing in the same place for a long time. Sunflowers are feral in my garden; they end up here and there and everywhere. I’ve never noticed any detrimental effects on anything growing nearby.


@MashaZ and @MarkReed That’s good to know!

I’ll let you all know how this works.

@H.B Thanks for the thoughts on allelopathy; that makes sense.

I have seen alot of people in other groups etc say that sunflower alleopathy is not that much compared to other plants. Mainly from the leaves and mainly for a very short time only immediately where the leaves fell and decayed.
This is my first year growing sunflowers so we’ll see if things don’t like growing near them.

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I also have a lot of black walnut trees and haven’t really seen a problem with them either. Grass and various weeds grow right up to the trunks. Virginia Bluebells and other wildflowers grow under them too, as well as daffodils. On the other hand, I’ve never tried planting any kind of vegetables under or near them.

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Beans seem to be resistant both to black walnut and to sunflower toxins. I grow them in the part of my garden that receives a lot of fallen walnut leaves and fruit, and is underlain by roots and decaying stumps of black walnut. Will Bonsall has a chapter in his book about growing pole beans up sunflowers (and amaranth) instead of corn, which he has been doing successfully in Maine.
I’ve had good luck growing basil on the outside of a block of peppers, to shelter them from the side; perhaps bush beans would do even better. Peppers seem to be able to take quite a bit of sun straight down on the canopy, but sun from the sides results in sunscalded fruit, and surrounding them with something else gave me a lot more usable fruits
Anyone compiling a set of resistant vegetables might consider miner’s lettuce. It’s a native that does really well under walnuts and sunflowers–it seems to really appreciate the help in reducing competition.


Nice! I have really got to get some miner’s lettuce seeds.

I’m not sure about sunflowers, but many forms of allelopathy affect seeds but not mature plants. If you’re not planting direct, or if you’re planting the sunflowers after the other plants are established, it might not make much of a difference.

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I feel like I read that someplace too. That the sunflowers’ trick is to inhibit germination of seeds or affect yoing seedling’s ability to grow. Can’t remembee where it was I read that though…

I was researching allelopathy a while back. Juglones (walnut) work by depriving the competition of oxygen, if I remember correctly. I think sunflower was one of those that inhibits germination.

One of the things I learned from my native plant restoration efforts is that I have much greater success when I plant a seed mix of many different species rather than trying to install groups of individual containerized plants. The seed mixes allow for the plants to find the spots and the companions that they like. The plants make better choices than I do (even though I have tried to educate myself about the plants). I am very interested to pursue the same approach with vegetable gardening. The main challenge is to have sufficient quantity of seed. I’m working on the seed increase at this point. I think that surface-sown seeds are the best kinds to start with to put in a mix.

I think of a seed mix as a sort of holographic representation of an ecosystem…


And then there are the foundation plants which tend to have larger seeds that need to be buried. Beans, Sunflowers, Squash, Corn. The foundation plants don’t necessarily need to come first, though. Timing is a variable to explore.