I just bought two Encore azaleas for our flower beds. The instructions say they will grow to be approximately 3 1/2 feet wide by 4 feet tall. This will fill our space when they are fully grown. About how long does it take to reach this size? What is the best fertilizer for these plant?
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 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
Fertilizer depends on your soil. The basic rule of thumb is 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.