Posted: 30/10/2014 at 09:04
Yes, you can control its size but you need to know what type it is as that affects pruning time and extent. Get it wrong and you'll get no flowers.
Mopheads and lace caps flower on stems produced the previous year and before so you could start by taking out one third of the stems in spring after the worst frosts, taking cuts at regular intervals to keep the shrub balanced inshape. This will encourage it to start early, producing new stems for the following year. Give it a good general feed and an instant tonic of liquid rose or tomato food to encourage healthy new growth with good flower power.
Once flowering finishes on the remaining stems, take them all back as far as you need to get the size you want, bearing in mind that new growth will make it bigger again.
If you have the paniculata type with large, cone-shaped flowers they flower on new wood and can be pruned back hard in late Feb or March depending on how cold your winter is. Again, give them a good feed to encourage good growth.
This is what the RHS advises - https://www.rhs.org.uk/advice/profile?PID=516