Powdery Mildew isn't going to kill your plant. If you're going to be growing hydrangeas, you might just have to learn to live with it at the end of the season. Some varieties are more resistant.

I think the idea with baking soda is to change the Ph of the leave to discourage fungus. I've used soda and oil on other plants and although it seemed to help a bit, I really didn't like the oily look. I'm experimenting with sulfur.

Good luck. Hay.

I've never tried the recipe you desribed, but I recently experimented with a solution of very diluted bleach on a few areas of a Hydrangea Nigra that was just completely overrun with powdery mildew and it actually worked really well.

I used about a tsp. of bleach with a quart of water in a spray bottle. I sprayed the affected leaves, then carefully wiped the leaves down with a soft cloth, then sprayed them again and left it. The rest of the plant I applied an over the counter product specifically designed for powdery mildew (got it at Lowe's).

The section of plant I treated with bleach water is almost completely mildew free and (believe it or not) the leaves look healthy and green. The section of plant that I used the stuff from Lowe's, is still covered in mildew and looks awful.

I'm not recommending anyone do what I did, so please don't send me hate-mail if you try this and your hydrangea dies. Just letting you know what worked for me.

Thanks so much for the information. It's nice to know that this will not kill my hydrangea. So, it sounds like it's just trial and error to find out what can get the mildew under control. Thanks so much again.