Answer: Most plants tolerate a range of pH. Junipers are known for being especially adaptable and grow well in a wide variety of landscape situations nation wide.
Here is a reference table showing pH preferences for different shrubs. As you can see, the different types of junipers may have a slightly different preference under ideal conditions.
Juniperus squamata however is not listed, and I personally have never heard it described as having a special preference one way or the other. So I checked in Michael Dirr's Manual of Woody Landscape Plants; this well-respected reference generally indicates soil and other cultural conditions if they are significant or important to success with a plant. Under this plant, he simply says in regard to soil: "Adaptable, tolerates dry soils ..." So unless your soil is extremely alkaline, I would not expect that to be the problem.
My inclination, without seeing the plant or knowing the pH and other soil conditions, is to suggest that the site may not be well enough drained for this plant -- it is often grown successfully in rock gardens which drain very quickly. If you have heavy clay based soil or have worked in a lot of organic matter without sand, it maybe that the soil is not draining and is instead become water logged. This would cause root problems, and overwatering (or poor drainage) usually is signaled by browning beginning at the base of the plant.
Junipers as a group also need good air circulation, so if you are mulching heavily under it and right up against it, this may be holding humidity against the foliage and causing a problem. If you are watering overhead or at ground level but frequently, this can also raise the humidity to a high level and invite disease problems.
There are some fungal diseases that can affect junipers and cause browning, usually from the bottom up or on one side moving up progressively. It is possible that is what you are seeing; to identify the specific cause you may need to work with your professionally trained nurseryman and possibly run some pathology tests. That way you would know for sure.
As far as mulch affecting the soil pH, it is possible that used in excessive quantity it might affect it. Some types of wood or bark mulch raise it, some lower it over time, but the effect is gradual. Soil testing would be the only way to know if something like this has occurred.
I'm sorry I can't tell you specifically what has happened to your plants, but I hope this helps you trouble shoot.
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