I planted a viburnum odoratissimum hedge 3 years ago and still no rapid growth
in fact despite so much love and water and fertiliser.... prepared before planting by digging a trench and filling with compost and loam... nothing more I could've done... maybe should've stuck with photinia robusta!
Certified GKH Gardening Expert
It is quite easy to "over-love" a plant to death. Always make sure to check soil fertility levels before planting or adding anything to ensure that it is not already full of nutrients. Once you have a soil test, you can begin to correct soil if necessary.
Viburnums are usually pretty self sufficient, not require much extra nutrients.
They can also be considered somewhat slow growing, comparatively.
These articles will help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm