Thanks for writing. How fast they grow depends on a lot of factors, including how large they are now, what the growing conditions are like, what kind of weather you have, etc.
A general rule is that the smaller a plant's mature size is, the slower it grows. So if you have a young plant, it may take 5 or more years to reach its full size.
What's the best fertilizer to use? That depends on your soil though the basic rule of thumb is that a general-purpose garden fertilizer is a good bet. If you have rich soil or amend it with compost, you probably don't need any fertilizer. If your soil has a medium to high pH, you might look at a product designed for use on hollies/evergreens/azaleas/rhododendrons that prefer acidic soil.
Thanks for writing. I hope this helps!
---Justin, Senior Garden Editor, BHG.com"