Dig it up, wash the roots, replant in more suitable soil.

Need more info. For instance, plants don't suddenly turn yellow in several days unless the root system is severely damaged. Then, too, root function is moving really slow at this time of year. So the reaction is likely to be even more delayed.

You said "just replaced a patio slab." But what's the interval between replacing the slab and the yellowing of leaves?

Also were any roots severed and/or removed?

Slab was replaced in November when it was raining heavily. Then the workman washed the exposed aggregate and it all ran into the garden where the rhodie is. It was a mess. I think bboy is right, I should dig it up, wash off the roots and relocate it. Otherwise, I think it will look quite sick for years. Perhaps some lime loving plants should be planted at the edge of the patio. I just hoped there was a magic antidote to lime. Thanks guys.

When the wrong pH fertilizer was used at a local rhododendron collection the result was bright yellow foliage.

Keep us updated on how your rhodie is doing and on a final diagnosis of the condition. Good opportunity to plant hellebores or hart's tongue fern.

Bboy's idea of digging it up, washing it off, and replacing the soil is the best idea, but you could try making coffee, lots of coffee. Cool it and water the plant with it. Use the grounds as mulch. Coffee is acid.

Digging up an old established rhodie is going to be a lot of work, and traumatic to the rhodie. Try adding gypsum to counteract the lime, or topdressing with peat moss, or fertilizing in spring with an acidic fertilizer.

Gypsum won't counteract the lime. It's Calcium sulphate, so it will add even more Calcium to the soil. Also, it doesn't have much effect on pH. Powdered sulfur or Ammonium sulfate fertilizer have a strong acidifying effect. I would not use Aluminum Sulphate fertilizer.

One of the reasons that rhodies don't like lime is that it makes metallic trace elements unavailable, like Iron and Manganese. You can compensate by adding chelated Iron to your soil, or applying it as a foliar spray in the spring.

Our NW soils are so acid that I would bet the rhodie will recover pretty quickly. Just keep an eye on it this spring.

Rhodies, even very mature ones, are quite amenable to digging and moving and now's a great time to do so. I'd consider lilydude's advice - remove any obvious remains of the concrete and adjust the pH by applying sulfur - as noted, gypsum has no impact on pH. Or you can apply the iron chelate now and fertilizing rhodies is recommended in either late winter (February) or in early fall, so applying now is fine. Generally the iron chelate or a listed acid-lover ARC fertilizer (and most contain chelated iron) is enough to offset the leaching of lime from concrete structures or surfaces.

Thanks for the suggestions. There are actually two rhodies impacted by the concrete run off and one is very old. Their trunks are probably 30 inches away from the worst of the run off although I know some was splashed onto their leaves as well. Given the difficulty of digging them up and washing roots off, I'd sure rather try the idea of counteracting the lime by adding acidic amendments, etc now. Both rhodies have great buds on them. I'll visit the garden supply store today and get some sulphur and good rhodie fertilizer. It's going to be interesting.

They're already been traumatized enough to have turned yellow, I'd consider getting them away from the contaminated soil enough of an emergency to want to pop them out and wash them, get them in suitable soil - and hope that was adequate. I would not want to subject them to additional chemical exposure - it takes a lot of alteration to change the pH of a soil even one pH point - too much of a change to do all at once. The soil is a community, not a cake mix. Jerking the pH around would be expected to be detrimental.

Hi Dottie - I agree with bboy - good luck

So, I had my handyman dig up the two rhodies and move them away from the lime. One is sulking, but will live. The other (my favorite of course) was destroyed, the trunk parted company with the roots. So now, I have bare spots in this perennial garden, room for 3 or 4 shrubs. I think I'll try something different, with colour for other times of the year. Any suggestions for shrubs that can be in dappled shade and are deer resistent?