Question
Hi Long Island Gardener. I'm a transplant to Indiana, so I bought a few really nice rhododendrons for my front yard.  They get full morning sun, and no afternoon sun.  This spring the leaves are green, but quite yellowish.  They've definitely bloomed, but the leaves just don't look as green as I think they should.  I am reluctant to use ironite.  Any other suggestions?  A foliar treatment perhaps?  

Answer
Yellow areas between green veins is a sure sign of Chlorosis.  When people hear that, EVERYBODY wants to run down to the garden center and pick up Iron for their plants.  Ironate, Miracle Gro with Iron, Scotts with Iron blahblahblah.

There's a big  problem with that.  You see, most soil has PLENTY of Iron in it.

But plants can't always get to it.

Your solution lies in making it easy for your Rhododendron to get the Iron it needs out of the soil -- something it can't do now.  My money says that's because your soil is too Alkaline.

All-yellow leaves are a different problem.  But 9 out of 10 times, shrubs with yellow leaves and green veins are growing in a pH that is WAY too high for its own good.

Yes, you could make this better for a little while with an Iron/Ferrous Sulfate leaf spray.  But that won't work long term.

But not forever.

To get a real improvement, you are going to need to fix that pH.

Here's what you should do, Samantha.

Do you drink Coffee in the morning?

Run down to your local Starbucks and get one of their free bags of used coffee grounds.  Even better, get a dozen bags.  They're free and they're the best thing going.

Coffee grounds repel Slugs.  They attract Earthworms.  They condition soil.  And BEST of all, Coffee is a TERRIFIC acidic soil conditioner, as any coffeelover who has ever had Ulcers or Heartburn can tell you.  One tester clocked a cup of Starbucks at 6.3.  Coffee grounds, which have been diluted with water, have a relatively neutral pH of around 6.7.  So I think you can see why your Rhododendron would love your Coffee grounds.

They would love your leftover Black Coffee even more.

Coffee (black) and Grounds (which has an N-P-K ration of 2-0.3-0.2) are very high in Nitrogen and other nutrients.  People tend to forget that Rhododendrons need Nitrogen.

Note that this is very different from the common 30-10-10 "evergreens" fertilizer sold by most garden suppliers.  That much Nitrogen is great for foliage.  But it will do nothing for flowers and if applied past late spring will inevitably stimulate leaves well past the frost safety zone in autumn.  It will also inhibit flower production.

The Starbucks grounds come in slick little sealed bags.  All you have to do is ask.  Call in advance -- lots of people know nothing about this and after a while, Starbucks Corporate gets discouraged and they downplay it.  Nevertheless, these Grounds are just what the Doctor ordered for EVERYBODY's Roses, Evergreens, Gardenias, Blueberries, Lilies.  They are terrific.  Including your Rhododendron in your morning coffee routine will only bring good things along.

As far as the morning sun site, Rhododendrons thrive in lightly shaded positions.  They are more inclined to leaf damage from sun that is too bright -- sunscorch on the leaves and drying out from lack of moisture would cause more problems, especially in warmer climates than yours. In your cold Indiana climates, Rhododendron perform best with protection from wind and from strong winter sun.
 
On the other hand, a regular deep Summer watering will encourage deeper roots for these shallow-rooted shrubs, increasing the odds they will get through Winter unscathed.

Those new, improved roots will also be better equipped to tap soil nutrients.

So, no, you do not need Ironite.  But you do need to do a soil correction.  This can't be done overnight.  You'd better get started asap.  Thanks for writing.