I may be missing something, but what type of Podocarpus can be planted only 18” from a wall?

Its not ideal but you'd basically have one-sided foliage on the bottom until the hedge reaches the top of the wall, then it would grow both-sided. We've done it before with really good results at another house, but we can probably move these ones to 2' or so out. That said, I was more so wondering about the depth they need above the concrete.

And be aware that no shrubbery will ameliorate sound.

Are you in FL or CA?

consider discussing your project with these peeps ...

https://www.instanthedge.com/

perhaps they can recommend something more suited to your project.. or agree with you.. how do i know.. lol ..

ken

@UpperBayGardener (zone 7) California.

Depending on the species selected, growing a podocarpus in a container or restricted planting area is certainly possible. As a genus, they tend not have a very aggressive root system. But be advised they are unlikely to grow as quickly or as large as a similar plant would if in the ground with a unrestricted root mass.

I would look at a planter that is a minimum of 24 inches deep. And a more distant placement away from the wall than 18 inches is also advised, to maximize both growth and longevity.

And take heed of the previous statement that these - or any other hedging plant - will do very little to ameliorate any sound.