Sunflowers do not have an inhibiting hormone that I am aware of. The genetics people are working on getting these traits in plants however and there may be some varieties out there that have it...I am just not aware of any and not of the seed that I carry has it.

Wheat and Sumac have these inhibitors however. Neat stuff.

Sunflowers do have a good ability to grow within competition. The heads will be smaller but there are fairly tolerant. That is why sometimes they grow under neat the bird feeder.

Great for pheasant, turkey, quail and other birds. High in oil and protein and very digestiable. Cereal grains are one of my favorites.

Land DR
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