Aluminum is harmful... it acidifies soil.

You said "declined quickly after transplant"

Such events typically follow a plating problem, or a problem of aftercare, usually related to water, either too much or too little. The key is to get the water directly into the rootball.

Soil acidifiers - like most other soil amendments - are not harmful if used correctly. They do not act particularly rapidly so generally require some planning ahead and with most soil types will need to be used repeatedly, as buffering will tend to bring the soil back to its natural pH.

Aluminum is not an acidifer - aluminum sulfate is. One must be cautious when using this product as aluminum toxicity can build up easily if overapplied and a great many plants are vulnerable to aluminum toxicity, rhododendrons especially. I wouldn't consider phosphorus to be a very efficient acidifer and it too can create toxic conditions if overapplied plus can contribute to groundwater pollution. Sulfur is kind of the standard of soil acidifiers. Cottonseed meal will work also.

As to the accuracy of the home test kits.....of all the home soil test kits available, one tends to get better results with the pH kits than with the others. But again, they must be used correctly. Tap water can influence the results so you should be using distilled water with the tests.

I'm going to lean with jean on this one. Plants tolerate a pretty wide range of soil pH and even if in a very unsuitable pH will decline only over time, not very rapidly. If the rhodies are thriving, chances are the pieris and hemlock should be happy in similar soil, so some sort of planting or aftercare issues - not soil issues - are indicated.

If you have the acid lovers near your lawn and you fertilize regularly such high nitrogen content of that will, in time, bring the acidity up. Such is the reason why some people regularly use lime on their lawns to bring the pH up.
Your reading is neutral 7, and cant be blamed for any undue dilemma a plant, whether alkaline or acid, is feeling pain from.
Garden sulfur does bring about acid condition to the soil it is given. Many acid loving plants are given sulfur as a regular spring ritual to bring the pH to the acid side for their benefit. Since, as noted, such change of pH takes time to wind its way through the soil, it should be planned ahead of time when the frost leaves the ground.
There are also other ways to help your acid lovers besides tryign to abruptly change the pH, such as mulching with materials that are acid in themselves. Such things as oak leaves, evergreen needles, peat moss, to name a couple.
Plants can use these mulches to help the soil retain its pH longer and in these cases, helps the soil not dry out so much--retains moisture longer. With regard to rhodos, this can be very important since the rhodo does not retain moisture long and is though a very important feature of the plant to remain on the damp side.
There are certain signs you might acquaint yourself with if a plant needs uptaking of an acidifier.
Leaf tips might brown showing an over or under abundance of fertilizer or the soil needs more acidifiction.
It takes time, as noted, to make its way through soil....but you should not try to speed things up by using more than you should.

Generally, fertilizer given acid loving plants, does not materially change the pH, it is not a soil conditioner.
Garden sulfur is. Fertilizer might keep the pH at a more even scale.

Doubtful the pH played a roll in the decline of your hemlock. I grow many hemlocks (a junkie, you know) and my pH is over 7.

tj

Many soil "acidifiers" can be harmful to the Soil Food Web and can kill the wee buggers if used improperly and in soils with too little organic matter to help support the SFW. Aluminum Sulfate will kill any earthworm that makes contact with it and if that will happen the same thing will happen to smaller soil dwelling thingys. Sulfur will also kill off members of the Soil Food Web as can lime if applied wrongly.
Why is your soil pH where it is? That is something your home soil test will not tell you. What is the balance between your soil Calcium and Magnesium?

Just a couple of little clarifications:
If you have the acid lovers near your lawn and you fertilize regularly such high nitrogen content of that will, in time, bring the acidity up.
That depends on the nitrogen source. Ammonium and urea based nitrogen fertilizers - yes. Nitrate based nitrogen fertilizers: No.

There are also other ways to help your acid lovers besides tryign to abruptly change the pH, such as mulching with materials that are acid in themselves. Such things as oak leaves, evergreen needles, peat moss, to name a couple.
Some organic materials are acid but in order to shift the pH towards acid must be incorporated and at a relatively high volume. Even that effect will vary widly depending on the type of organic, its stage of decomposition and buffering capacity of the soil. Mulching with pine needles, for example, won't acidify. It's an old garden myth.

Links to good discussions on Gardenweb:

Ca + Master Gardeners Manual

pH over time

water ph and soil ph

Links to useful discussions not on Gardenweb:

MG Manual Reference Ch. 2, pp. 9

Alkalinity (Buffering Capacity) Very important in my estimation.

City of Boulder/USGS Water Quality Monitoring

We never fertilize the lawn, the lawn is more weeds than grass, we're in the country and so what covers the dirt gets mowed. I watered the hemlock plenty and have planted about 50+ trees and haven't lost more than a couple and of the couple they are 2 hemlocks!I drag a hose to all my baby trees in the summer if it doesn't rain good for a while, I know where roots start and where the trunk ends, slice the rootball to break up tangles. so I planted correctly.I was referring to sulfur not the aluminum stuff. The article said it turns into sulfuric acid and kills soil fungi. So the process that helps also hurts. The leaf mulching I've been doing for a couple of years. I get leaves from the township with a little grass in it sometimes but not much and mulch all the trees and beds put pine needles so the leaves stay put, so unless it has to be put in the soil instead of on the soil my efforts should have got me on my way somehow. Tsuga junkie I can grow Rhodies and hygrangea fine but hemlock hates me ! I have sown some seed of local hemlock and spring will be the drumroll I have 2 different locations of hemlock seed. So if the seeds germinate, they are local seed, no transplant stress, no loss of roots by having to cut any and if they sprout and croak I am giving up on hemlock!poaky1

Hemlocks grow best as understory trees in soils well emdowed with organic matter that is evenly moist but well drained and is slightly acidic. Many times I see these trees palnted as specimen trees exposed to fairly high winds that tend to dry them out and they show severe signs of distress and are infested with the Wooly Adelgid.

Sorry to drag this thread on but I am trying the cones or seed on the north side of a tall wood fence there is a shed in the way of most northern winds I have decided against sulfur if tsugajunkie can grow them in over 7 PH that's not the problem and I don't want to mess with the fungus and microbes and all that. I will keep up with leaves, bunny poop with sawdust mixed in and wood chip mulch in the areas I have future (acidic) planting planned I am hopeful about these hemlock seeds, I collected soil from under adult hemlock in the woods in case it's fungus or something they need.If they don't make it, I'll have no clue as to why I have a pin oak rhodies and hygrangea that are happy in my soil and they are within 20 ft of where these seeds are.Thanks all for your input.

A couple of things kimmsr. Hemlocks are not understory trees. They have grown to 150 feet or more and are quite happy in full sun given proper moisture- as most canopy trees are. And where have you see Hemlock Wolly Adelgid in Michigan? They are having a hard time getting west of the Appalachian Mountains. Now, the OP is in PA and HWA may be a concern there but it can be spotted and controlled on a small specimen plant.

tj

Here is a link that might be useful: Something fuzzy on your glasses

I am right in the SW county that says newly infested 2009, ain't that somethin? Well, if I encounter it what's the solution a dormant oil?I will surely get at least 1 tree from all the cones they were on the ground and not quite open yet and I saw seeds in 1 of the cones. Another thing my Forest farm fall catalog says hemlock grows on chalk, isn't that limey? Isn't chalk alkalin? Maybe my soil is too acidic for them! I was shocked to read that.

No, your soil is not too acidic. Some stands have been found in soil with a pH in the 4s. Hemlocks tolerate a wide range of pH, perhaps the widest among conifers. Soil type is much more important but some of mine are in pretty thick clay which is hardest on them. Be aware that the germination rate is quite low for hemlocks. As for HWA control, check the link. Wordy but complete. Insecticidal soap is what I'd use first. Easiest to use and less chance for error. If your library has it, check out the book:

"The Cultivated Hemlocks" by John Swartley
Timber Press
Portland, Oregon
1984
186pp

An easy read for those with an interest in hemlocks.

An example of a dwarf cultivar of mine grown in clay soil amended only with top dressings of compost for about 10 years. Tsuga canadensis 'Jervis' Variegated Solomon's Seal behind.

{{gwi:314164}}

tj

Here is a link that might be useful: HWA Control

I messed up on the hemlock on chalk,I looked through the catalog to confirm what I wrote and couldn't find it. Must have been too much bedtime reading. I must have mixed up the plants from sleepy reading, sorry for the mixup.I have the variegated solomons seal too.poaky1