Just so we're all on the same page ... What exactly do you mean by "Christmas tree toppers"?

What was the given rationale for not being able to reuse the soil?

Here in Minnesota nurserys sell bundles of evergreen boughs that are cut from the tops of the pine trees. Thus "Christmas tree toppers". These you stick into large pots of soil, and was told that the pines would contaminate the soil for other plantings. Sorry I didn't make myself clear!

That's a bunch of horsepucky! Whoever told you that was talking out their backside. I stick evergreen boughs in all my outdoor planters and window boxes... I have for years. Come spring I pull them out and plant whatever my chosen plants are for the summer season. I have never had a problem with anything growing. The only thing I do before replanting is add in a bit of fresh potting mix to bring the level of the soil back up to where it needs to be.... And a handful or so of slow release fertilizer such as Osmocote.

Thanks Scott. I will follow your advice...don't you just hate that horsepucky!!