A good idea Elizabeth but, I disagree that soil pH is/was the causal agent. High soil pH problems (pH at or above 7.0) are indeed present in most of the Dallas/Fort Worth Metroplex so hydrangeas need to be amended regularly. They normally tolerate this soil condition, showing no symptoms but only up to a point. Once that threshold is crossed, the plant is unable to absorb sufficient levels of some minerals (phosphorus, iron, manganese, boron and copper) while, at the same time, facilitating the absorption of other minerals (nitrogen, potassium, sulphur, calcium, magnesium and molybdenum). Physiological symptoms become evident once the plant is unable to uptake enough of some minerals like iron.
You should be able to observe the following symptoms when the soil is too alkaline: yellowing of leaves except for the leaf veins which remain dark green. This symptom is progressive, starting with leaves changing from dark green to light green and then to yellow. New leaves will be the first ones to display this problem; older leaves will follow but much later. In some severe cases, the yellow leaves turn can turn white although eventually, they will turn brown. A picture of a hydrangea starting to suffer from iron chlorosis can be seen in the link below. If you look at the affected leaves in MikeÃ¢â‚¬â„¢s pictures, you will notice that they did not show these symptoms.
https://search.yahoo.com/search?ei=utf-8 ... ture&type=
But your suggestion of a soil test is very timely indeed. With sales usually down during the winter months, some plant nurseries offer soil test services for free. You bring the soil samples to them and they send them for analysis and contact you back when done. Locally, CallowayÃ¢â‚¬â„¢s Nursery does this in either January or February. To compensate them for this, I try to purchase some amendments (compost, mulch, expanded shale, green sand, etc) to somewhat make up for the cost of the service. In this area, the Ã¢â‚¬Å“big storesÃ¢â‚¬