I can't tell for sure from the photo if that is chlorosis, a close up of a leaf may have been better.

But, a foliage spray of a chelated iron product should have shown results in about 2 weeks if lack of iron due to PH was the problem. Chlorosis could also be a lack of magnesium, a spray of roughly 2 T Epsom salts in a gal of water should indicate if magnesium was low, leaves would respond by greening within several days.

But again, I'm not sure that is chlorosis. Cultivating (as in amending the soil) around the plant after planting isn't recommended - rhododendrons will establish a surface network of feeder roots just below the soil extending as wide as the widest stems. Do you have reason to know the approximate ph of your soil, and do you think of it as being of average fertility when you consider the performance of other plants in your landscape?

I don't know the relative pH of the soil, but all my other plants are doing fine. I grow many tropicals in the ground up here during the summer months ... palms, magnolias, bananas, mountain laurels. They look perfect.

Here are some closeup shots of the leaves today.

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Here is an older leaf -- all green.

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Here is a shot from earlier in the year of the front yard all decked out.

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Here is the rhodo in bloom earlier this summer.

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As for working the peat moss in the soil, I didn't dig really deep as I understand about the feeder roots. I basically spread it out on top and then worked it in to only the top 1/2 inch of soil or so to mix it in. Then I simply mulched over the top and soaked it with the hose.

Any ideas?

I don't grow palms or bananas, but soil acidic enough for kalmia and magnolia should be acidic enough for rhododendron. That still doesn't look like chlorosis to me, I wonder if not some kind of environmental stress happening while the plant was still establishing. Did you experience some of the heat that gardeners E of me had this summer?
I'm not going to say drought, the rest of your garden looks too well tended, irrigated for that...and overall your rhododendron looks healthy with just that slight discoloration. Was it correctly planted with the rootball opened up so roots are reaching out into the surrounding soils? I think if it were mine I would just keep an eye on it, see what Spring brings, and not try to do anything else to correct this Fall.

Yes, I loosened up the rootball before planting. About a week after planting we had 3 days near 100F, and then the rest of summer we were 85-95F during the day and 65-75F at night. Real warm summer overall. I kept everything irrigated, though. The rhodo gets several hours of shade from the surrounding trees, but also gets several hours of sun. The shade it does get is really bright, however.

Maybe the leaves that grew immediately after planting were just stressed. I guess I will wait and see what next year brings? I plan on spraying it with Wilt Pruf in a few weeks to help prevent leaf dessication this winter.

Maybe next spring I'll test the soil pH in April with one of those pH test kits. Give the peat moss time to work its way in the soil this winter. I also plan on mulching with pine nuggets next year which should help keep things heading toward acid.

Yellowing of leaf edges has been noted in gardens where sandy soil conditions or root competition with other plants caused insufficient soil moisture and nutrients. Usually incorporating organic material in the soil and removing the plants with the competing roots solved the problem. Care must be taken not to disturb the roots of the rhododendrons and azaleas. Hence it is best to prepare the soil adequately before planting. The tops of most competing plants can be removed leaving the offending roots in the ground and the offending roots will simply decay and pose no problem.

Do not culitivate at all, even the top 1/2 inch. If a soil test indicates your soil is not acid enough, powdered sulfur is the best solution. It is slow to act, but lasts a very long time.

How To Care For Rhododendrons

Steve Henning
Reading, PA USA Zone 6