Tree Base Flower Box

So I decided to make a shallow planter box around it. I picked up two 8-foot 3.5 x 3.5” pressure treated garden ties.  

Then I cut them both in half, to make a 4 x 4’ box.

I laid the four pieces of wood around the tree and measured from the tree trunk to the box on all four sides to make sure the box was centered. Then I dug up all the weeds and trimmed the grass as short as possible inside the box.  

Then I screwed the wood together using 5" deck screws - two screws on each corner.

I placed cardboard on the ground to kill the grass. I removed all the tape, stickers and labels from the boxes to make sure I wasn’t burying anything environmentally unfriendly. The cardboard will break down fairly quickly.

I filled the box with soil. I kept is shallow and fluffy because I didn’t want it to be too deep or heavy over the tree roots.  

Update: After receiving feedback from an experienced horticulturist in the "questions" section below I removed some of the soil - down to 3/4". I also pulled the soil away from the tree trunk - there's basically just a sprinkle near the trunk now - enough to cover the cardboard.

The two cut ends of wood that were visible (the other two were inside and not visible) I stained with provincial gel stain, applied with a cloth.

Then I added a few flowers to the box. I decided to just plant a few things this year, so the cardboard boxes will get lots of moisture and break down faster. But I’ll add a few more perennials next summer. 

I will keep a close eye on the tree to make sure there are no ill effects. But the local garden center staff assures me this shallow bed will not damage my cute little tree. 

And here it is! It will be so nice not having to get into pretzel positions while I’m cutting the grass!

After learning that I shouldn't put soil too close to the trunk I relocated the sweet william flowers that I had planted up against the trunk. I love the way it looked - but I love the tree more and want to ensure it remains healthy!

And this is how it looked after I removed some of the soil and relocated the flowers I had planted up against the trunk. I think it still looks very pretty. And it still serves the exact same purpose I built it for - easier mowing around the tree. :)