Don't know the answer to your question but another option is to use hulled sunflowers. I think the problem is with the hulls.

I don't know about the effect of black oil sunflower seed hulls on perennials, but all my bird books recommend using them rather than striped sunflower seeds. I use the black oil seeds in feeders not in flowerbeds and No Mess by Wilds Birds Unlimited for those feeders in flowerbeds. We lost our Wild Birds store here in Tyler so I buy several large bags every time I go to Houston to visit my daughter.

I thought the sunflowers themselves, put out a toxin to prevent other plants around them. This toxin would also be in the seeds. I buy the cheaper striped sunflowers, and the hulls thrown about do make a bare area in spring grass growth.

Seeds might also be treated with something, but I had not heard of it. Perhaps you could call a company name on the seed bag.

I feed a lot of sunflowers during winter,usually a couple hundred pounds. With the raise in prices (doubled here, now $20 for 50#) I can't afford hulled or even the black oilers. My local birds like the sunflowers and suet I put out. We do have fields with unmowed weeds for birds liking seeds like thistle. With my quantity of seeds used, they make a large pile of hulls. I rake up my hulls come spring, use them in places I don't want growth of weeds or grass.

Search for 'allelopathic' to see how sunflowers naturally keep other plants from growing.

Yes, they are not "treated" but the hulls do have allelopathic properties that discourage and can even kill other plants. Pretty effective against weeds but not so good with desirable plantings :-) Buy the hulled seeds on sunflower chips - they're more expensive but worth it regarding your perennials.

And a 'master gardener' should know better!

Thank you all! I didn't know that there are plants that are allelopathic - very interesting! I decided I would just buy the hulled seeds - less mess and no worries about the plants. Thanks again for helping me learn something!

By the way, Gardengal, the perennials were in the ground before the birdfeeder, so the master gardener did know better, and that's how I found out that BOSS were not good to use in the feeder. Looks like he knew what he was talking about!

Thanks again to all of you!

Deb, my point was that a master gardener should be aware of allelopathy - it's pretty darn common in the plant world and I can't imagine it not be presented as part of their training - and that sunflower seed hulls possess this property and are not "treated" with some sort of chemical or other plant growth inhibitor.

We put out a couple of large bird feeders in the garden this year with BOSS. I had wondered why a handful of my quite mature perennials bit the dust. Now I understand why. Thank you all for the information.

I'd been noticing the disappearance of grass in the areas where the BOSS seeds and hulls fall, so googled "toxic effect of black-oil sunflower seeds on plants" and zowie! found all this information!

What about the sugar maple that my feeder's hanging from? Any harm to it?
And how far away is safe for other plants, such as hastas?