Q: This is the first time my hydrangea has bloomed in 5 years. Can you tell me why the blooms are short and stubby.
A: Congratulations – you sent me a picture of something I’ve never seen before!
I sent the pix to hydrangea experts Gene Griffith and Elizabeth Dean; they sent them to hydrangea breeder Dr Michael Dirr.
The consensus is that your hydrangea is infected with a virus, possibly hydrangea chlorotic mottle virus, a carlavirus. It is spread from plant to plant by aphids but your plant could have been infected when you bought it.
Your best bet now is to dig out and destroy this plant before it infects others. If you have other hydrangeas, keep an eye on them and do the same if they begin exhibiting symptoms.
For a completely natural sleep inducing experience, read this paper on hydrangea viruses.