I would make sure that the soil is constantly moist since dry & wet cycles can cause the flower buds and blooms to be aborted. I would also do a soil test to phosphate levels in the soil. You can do a soil test or purchase a soil test kit for that. You did not say how much sun they get (from when to when) but I would make sure they get shade starting at lunch time or thereabouts.

Thanks for the information. The three plants get morning sun and are fully shaded in the PM. As far as watering goes, they get regular waterings from spring to fall since I have an irrigation system. I will do a soil test this weekend and post the results! I wish I could post a picture on this forum - I've got a few of the flower buds, but can't figure out how to post pictures!

You can open an account with a service like photobucket and download the pictures there. Then you can put a link to them from here. The Test Forum can be used to "play" with pictures.

Hello,

Sorry for the delayed response. The soil test around the oak leaf hydrangeas came back as:

pH 7.3
Nitrogen: Depleted
Phosphorus: Surplus
Potassium: Deficient

Do I just put down a slow release fertilizer in early spring to address this? Is the lack of nitrogen and potassium causing the flower problem?

Thanks for any help!

It would be a good idea to add some compost, blood meal and wood ash. Other chemical alternatives include muriate of potash and balanced slow-release fertilizers.

Thank you all for the help. I just put down some Back to Nature composted cotton burrs and manure mixture around the plants and will soon sprinkle some 10-10-10 slow release fertilizer for the fall/winter.

Here are a couple of pictures of the plants. Again, any suggestions or advice is greatly appreciated!

http://i60.photobucket.com/albums/h15/nfowife/Hydran/DSC_7985.jpg

http://i60.photobucket.com/albums/h15/nfowife/Hydran/DSC_7986.jpg

Hello,
I think balancing out your soil a bit with a good slow-release fertilizer will probably help. But I also wonder how much sun your oakleafs are getting. They can take a good bit (almost full), and will be much less likely to bloom in shadier spots. I would be careful keeping the soil wet continuously though, as oakleafs tend to be sensitive to wet feet, and can be drowned much more easily than mopheads and lacecaps. They don't mind frequent watering, but need good drainage. Good luck!

Wow, thank you for the advice. I will soon drop some slow release, balanced fertilizer around the plants. I too think that they may not be getting enough direct sun. Very frustrating because I know what the plants could look like!