Excess aluminum (ionic) will act as a nutrient (uptake) blocker. The question is: at what point would it be excessive? I've been told it affects all bulbs, tubers and underground vegitables like carrots and potatoes the same way. The real problem is that aluminum ions, like sodium ions (salt, road salt) are not very mobile and are not leached away from the soil readily. Consequently, the build up over time can defeat its intended purpose; your pH values may be the desired correctness, but a continued downward spiral of stunted growth and vigor in succeeding years would be evident. Yet, packaged aluminum sulfate is widely available and info on the packaging in bold type says: For Use With All Acid Loving Plants, it should be used with caution while keeping the undesirable aspects in mind. So, of the four sulfur products we've mentioned, aluminum suphate is probably the least desirable in the long run. As Rick says--probably best to stay away from it, if another is available.
I think it's accurate to say that ALL LILIES, as with most plants, benefit from a slightly acid soil, i.e. pH 6.5. for maximun nutrient uptake. I think we can also say that Orientals or anything with Oriental in it seems to require the lower pH values for maximun uptake. At the other extreme, I think we can say that Trumpets or anything with Trumpet in it will thrive at the highest pH levels of all, perhaps as high as 7.3. But they, too, also benefit from a lower pH and more or less, are just tolerant of higher pH, certainly not because they love it.
Don't expect to see immediate results from a lower pH this year. So much of this is tied into bulb building in the current year for next years performance. Like Rick says a nice healthy bulb that's had good uptake will winter over in tip top shape and have a vigorous start the following year--that's when you'll see the real results of lowering your pH.
Rick, you just reminded me. I need to check on something!
