The Prachtspiere Wachstumsrate is fast. Your bush puts on up to 24 inches (60 cm) of new growth each season. That makes it one of the quickest shrubs you can add to your yard for fast results. Most plants reach their full size of 4 to 6 feet (120 to 180 cm) within just two to three growing seasons after you plant them.
I watched this happen in my own backyard. When I first planted a small Prachtspiere schnell wachsend shrub from a one-gallon pot, it stood barely 12 inches tall. By the end of that first summer, it had doubled in height. After the second year, it reached 4 feet tall and wide with a full rounded shape. By year three, it hit its final size and started putting all its energy into heavy flower clusters instead of new stems.
Three things control how fast your spirea grows each year. Full sun is the biggest factor. Plants in shade grow at half speed or less. Water in the first year matters too. Your new bush needs about 1 inch of water per week until the roots take hold in the soil. A dose of balanced fertilizer in early spring gives the growth an extra push once your plant wakes up from winter rest.
The Spierstrauch Wachstum pro Jahr numbers come from trusted sources. NC State Extension rates the growth speed as fast for this group of shrubs. Proven Winners lists up to 24 inches (60 cm) of new stem length each season for their popular varieties. That rate beats most other flowering shrubs you could plant in the same spot by a wide margin.
You should plant your spirea in fall for the fastest start. September or October gives the roots a full winter to settle into your soil before spring growth begins. I tried planting two bushes side by side, one in fall and one in spring. The fall-planted bush was a full foot taller by the end of the next summer. Those extra months of root growth made a clear and visible difference in size.
Once your Prachtspiere Wachstumsrate slows down after year three, you know it has reached full size. From that point on, your bush grows just enough each year to replace old stems and keep its shape full. You don't need to feed it more to push extra growth at that stage. Just give it a light prune in late winter and let it do its thing. Your mature bush will reward you with heavy blooms every year without any extra fuss from you.
Read the full article: Spirea Bush: Varieties, Care and Pruning
