Q.White Hydrangeas
I have a granddaughter getting married in March and she wants white hydrangeas in her bouquet. Could you give me some advice on how to keep my white hydrangeas bushes white. Do I need to put a special fertilizer on after this season and should I prune the bush? Should I protect the bush with shade cloth when it flowers, as we have very hot weather in January/February?

Controlling the bloom quality to coincide with an exact date is quite difficult.
Optimize the care requirements and provide adequate nutrients and water to your plants.
Here are some links that will help refresh you on the care requirements.
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/growing-hydrangeas-hydrangea-care-guide.htm
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/fertilizing-hydrangeas.htm
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/prune-hydrangea-bushes-hydrangea-pruning-instructions.htm