Toxins from sunflower seeds

Does anyone know how long it takes for the toxins to leave the soil from sunflower seed hulls? Dad used the piles of black oil sunflower seed hulls below the bird feeders as mulch on about $200 worth of hostas, and nearly all died. I later found out why:
http://www.cababstractsplus.org/abstracts/Abstract.aspx?AcNo=20033015198

I can't find anything online about how long to wait until it's safe to plant again, and it would be too labor intensive to remove all the soil in that area. Thanks to anyone for any info!

Many moons ago I had read that Sunflower seeds could inhibit growth, but I didn't believe it 'cause the flowers that grow under my bird feeder seem to thrive on the stuff. I don't know the name of the flowers, they grow like a carpet and are a pretty blue.

Sorry I cannot be of help to you. What a shame that your hostas died :(

I wonder if just adding a bunch of compost would dilute the allelopathic chemicals enough to make the soil hospitable again?

I was wondering the same thing...maybe I could try it and plant just one cheap plant to test it, lol.

That would be interesting to find out about. Let us know how things go, please.