I recently read in Rodale's Organic Gardening Encyclopedia that aluminum sulfate should not be used to feed blueberries because it is toxic to beneficial microorganisms in the soil. Some gardeners here in So. California use aluminum sulfate to turn their pink hydrangea blooms blue. Is there an organic substitute? Will elemental sulfur do the trick?

The more acid the soil, the bluer the flower. The more alkaline the soil, the pinker the flower. You can use any organic acidifiers to boost the blue. Pine needles, chopped oak leaves, coffee and tea grounds, a little vinegar added to some compost and allowed to sit a bit (a LITTLE vinegar...in large doses, it is a weed killer)...etc...

There is a product called Agricultural sulpher that is usually used to acidify soil for edibles. If elemental sulphur is just sulphur with no other things in it, it will do but I wouldn'd know how much to use.

Do you know where I can get agricultural sulfur or elemental sulfur? I have tried the usual places.

Sulfur should be available from any farm co-op...but I much prefer coffee grounds! They acidify just enough to intensify the blue color, and the worms just go crazy.

I get my coffee grounds from the local diner, but you can also try going to Starbucks...if you leave a bucket and request espresso grounds, you won't have to sift out the filters.

Thanks for the tip. I'm there almost every day anyway.