Add dirt or mulch to these pots?

[arminius]

Hi - i started with 8 inch white pines 2 1/2 years ago in these 3# pots. They have grown well and now 3' tall. The dirt has settled quick a bit, now down about 4" inside the pots. I'd like to keep them in the pots 1 more year. Should i top them off with dirt or mulch before winter? thank you

 

[Oliver Buckle]

I would have a go at sliding them out and putting something under them, they look big enough to have a fair old root system to hold it together if you are careful. Break a bit of earth off the top where there are not too many roots and mix it into the top of what you have added, break up the bottom a little so the roots can escape the pot shape, slide it back in, then put some on top and go round tamping it into the edge with something thin so there is no gap.
I could be completely wrong mind, I shall be interested in what other people say.

 

[Charlie 001]

The soil structure in those pots has broken down (hence the level sinking). This will reduce the ”air” in the soil (roots need to breath too). Also the ability to hold moisture and the nutrients in the soil I imagine the roots are quite pot bound
I suggest repotting into something abit bigger using a nice loam based compost