how much sulfur

how much sulfur do I add to make hys blue--can adding too much harm the plant??

Yes, it can burn the plants' roots if you apply too much. You can also cause harm to certain nearby plants if you utilize aluminum sulphate to acidify the soil. Sulphur by itself would be fine but that compound is poisonouos to azaleas and rhododendrons. It is best to use soil sulphur, aka, elemental sulphur, aka, flowers of sulphur.

The process is complicated and sulphur must be re-applied forever annually. That is because the soil Ph will slowly drift back up to its old level. But the good thing is that you do not need to apply sulphur in large quantities once you get it to the level that produces the desired color hue.

So how do you proceed? Most people wing it and apply some until they get the color hue that looks good to them. To do it properly, you need (1) your current soil Ph, (2) the Ph that you want to lower the soil Ph to and (3) the type of soil that you have. A soil analysis will give you the Ph Level that your soil currently has. Then you add an appropriate amount of sulphur to lower the Ph to the value that you wish to have. After the sulphur has been applied, you need to measure the Ph Level again to see how far down the value changed. Then you add more sulphur is needed. For sandy soils, you will have to reduce the std. amount of sulphur while, for clay soils, you will have to increase it.

For example: to lower the ph from 7.5 to 6.0, apply three and a half pounds of sulphur per one-hundred square feet of good soil; two and a quarter pounds of sulphur per one-hundred square feet of sandy soil; five and a quarter pounds of sulphur per one-hundred square feet of clay soil.

In order to get blue flowers there also has to be aluminum present in the soil, that's why many people use the aluminum sulfate. I'm not sure how often soil has aluminum already naturally present vs when it has to be added, but if you drop your pH and your flowers aren't blue then that's probably why and I would add a bit of the aluminum sulfate at that point.

So just acidifying your soil by using large amounts of peat in the mix won't do it?

If there's already some aluminum present in the soil then I don't see why it wouldn't as long as the peat gets the pH into the right range.

Thank you!