I think it helps with hardiness. I do not mix it in with the soil for annuals but will shoot the shrubs with my tree root injector. Have to be careful if they are new plantings as it will bring them up some. Would work well as a drench to when planting.
On trees and some times shrubs I just use the PHC dry mix with the gel.
Might want to check because many growers are now using it so you may not need it.