Loading on 5/4 treated pine decking
Check the code for you area it likely specifies the minimum pound per square foot that a code compliant deck should support (for my area it's 50 pounds per square foot).
Based on a guess of the planter size based on board width my guess is you may have a problem. I'd also note that if you live in an area that gets snow then I definitely be concerned as the holly will hold snow (additional weight) and cause drifting just where you don't want it (yet more weight).
Have you considered the fake outdoor privacy vines you can buy?
Jonathan