Boxwood shrubs have been popular for centuries across the world and are considered one of the oldest known garden plants. Some boxwood grow up to 15 or 20 feet tall, while others are dwarf varieties that max out a foot tall and wide. Sergio Amiti // Getty ImagesHow Much Should You Water Boxwood? ‘North Star’ is a cold-hardy type that forms a tight, symmetrical globe shape that’s 3 feet tall and wide at maturity. Where to Buy Boxwood Shrubs