Question
If you feel this problem is not related to fertilizers, please suggest the area I should address my question to.

I live in zone 7, about 12 miles north of Baltimore.  I have an area in my backyard with about 600 sq. ft. of pachysandra.  The pachysandra was planted about twelve years ago and it is quite thick.  This year, in three distinct areas, the pachysandra is turning yellow (about 25 to 35 sq. ft. each area).  All of the other areas are a deep green.

Every year, around early May, I broadcast, by hand, HollyTone over the area (about the same time that I Spring feed my lawn). Every other year I also spread some Ironite to the area.

Any suggestions as to what steps I might take to eliminate the yellowing?

Your advice is appreciated.

Answer
You are welcome.. and thanks for the vote of confidence.
I do think the change from shade to sun is your problem, too.
You can dig up clumps and move them to areas with more shade. It is a shame to just get rid of them all together, but grass is a wonderful choice for sun.

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Typically leaves may yellow if the plants get too much sun or if fertilizer nutrients are lacking. It sounds like you are using enough fertilizer and hollytone / ionite are good sources, also to reduce the soil pH. Generally a lower soil pH is preferred with this cover, but it can make fertilizer ions unavailable. A pH between 5.5-6.0 is preferred.

This being said, the plants grow over a very wide range of pH 3.5 to 6.0 but to  trouble shoot properly, I would have a soil test done. At too high pH level can make micro nutrients unavailable to the plants.

Also, this spring try to use a fertilizer which has all micro nutrients such as Miracle Grow 15-30-15. Use 1 tsp per gallon of water and soak the ground thorughly. (you can mix larger batches in watering cans). I do agree with the use of hollytone, etc, but a single application of a fertilizer w/ all micro nutrients should be in order, too. A soil test will reveal any deficiencies, also.

The leaves may yellow if plants get too much sun Solution: Move plants to a shadier location or provide shade.

If the problem is brown leaves rather than yellow it can also be desicating winter winds.

Finally, patchysandra is subject to euynomus scale which are white bodied insects which suck juices out of the leaves. Spray in early April with dormant oil (available at garden centers). Also avoid using fallen leaves or compost to mulch the ground cover to avoid leaf blight. Use a well draining mulch such as pine straw or conocut coir.