Sunflowers, benefits to other plants?

First post, new to the permaculture concept but it seems to be an idea that makes a lot of sense. I've been trying to find out what benefit sunflowers give to surrounding plants, if any and haven't found anything so far. The reason is that I recently planted quite a few of thme as I have a lot of doves and was growing them to feed the doves later. However, in the last few weeks I've noticed that my tomato, cucumber, and eggplants that are within a foot of a sunflower plant are growing twice as fast as the ones NOT near a sunflower and am curious as to why.

That is an interesting observation. I was of the understanding that sunflowers exuded allopathic root chemicals, which stunt most vegetables grown close by. Cucumbers (and cucurbits in general) I believe are an exception, and the cukes are probably enjoying the bit of shade, shelter, and humidity that the sunflowers are providing. As for the tomatoes and eggplants, I am suprised. But then again, tomatoes and eggplants are weirdos a bit IME.

I've never noticed the allopathic effects your talking about and I let sunflowers self seed all around my plot and leave one here and one there every year. Can't say why your noticing more growth with plants around atm. but in autumn when the seed develops I net up the big heads for myself and let the birds 'go nuts' on the smaller ones, I've observed birds eating the seed and pooping on my garden as they chomp down giving me free fertilizer I will often let sunflowers grow around young fruit trees to take advantage of the bird poop.

I also leave to sunflowers standing in the ground as the ladybirds (I think yanks call em ladybugs) overwinter in the stems.

We'll see if how it affects their production, I've always been good at growing tomatoes, eggplants not so much, I'll get 4-7 eggplants per plant on average which I don't think is all that great, but WOW those eggplants are loving those sunflowers, they were about 8 inches high and looking "normal when the sunflowers sprouted. The sunflower got about 12 inches and the eggplants perked up but were still about 8 inches high (last week) now both the sunflowers and eggplants are over 24 inches, it's almost like the eggplants are trying to race the sunflowers. And several blooms on the eggies.

I think the boost in growth you see when plants grow next to sunflowers is due to shade and increased humidity. Most plants basically shut down under intense sun. This is observable on plants that despite being well watered wilt on very hot days. The plants are saying, "NO MORE SUN!!!" By providing a bit of shade the plant continues to grow on days with intense light.

Sunflowers can provide a useful trellice for climbers planted nearby, such as pole beans. Sort of like a "Three Sisters" design, except that the sunflowers can be both taller and stronger than most corn....

I have noticed the allelopathic effects. I tried for a three sisters garden with sunflowers instead of corn as corn is very pesty but it failed. I was looking into why and figured this out. There are allelopathic substances in the whole plant, leaves husk stall... when it rains allelopathic drops come off the leaves! Some plants tolerate it better than others.
One benefit is that sunflowers accumulate toxicity, I've heard. I'd you have contaminated land this would be good.

My guess would be the positive side-effects of the encouraged growth of mycorrhizae due to the presence of the sunflower...?... This would aid nutrient availability, suppress diseases, promote benefitial microflora and earthworms... But that is just a guess {shrug}

sunflower husks are definately alleopathic..they tend to kill most weeds around where feeders drop seed hulls