I've just read the other thread of yours on this subject. If you know its fully hardy, I wouldn't bother to mulch now - wait till spring, as growth begins, and the ground is moist, and then mulch with a mix of ericaceous compost and garden compost, if you really want to mulch it.

The best reason to mulch hardy varieties of Hydrangeas is to keep the roots cool and moist in a hot, dry summer. Florist's types may benefit from a deep, coarse mulch in fall, to keep it from dying completely in the occasional monster winter--like the last one.

Thank you Bamboo and Tug...I know the plant is hardy it has been in the garden for the last 4 or 5 years so will wait til spring and give it a bit of a mulch. Thank you both