I had a close call hurting my right knee while working at the greenhouse nursery back in '06. Two of us lifting a large tree into a pickup truck. We didn't get the count of 3 right. I foolishly set my knee under it to catch it and to let it down. With a grimmace we restarted our count and got it in, but uh...walking away my knee buckled under me. Maybe I should have gone see a doc, but over the next couple months it healed. That knee is still kind of weak until my coffee kicks in in the morning, then it's ok.
I forget the gallon size of pot it was, 3 foot wide and 3 foot deep, and I guess freshly watered. That was one difference I mentioned to Roxi that if I ever owned a nursery, the trees would be in the lightest weight potting soil possible, and the row stabilizers for the trees could include a long bar over their pots. We had a good system of tree supports at most places. But sometimes, rrr, she did not mind using heavy dirt type top soil.
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Oh Thistle, do take care of that knee, and coming from one who probably did it the same way, go see a doc. think...the future... it might be more, much more expensive NOT to go see your doctor! Also, gotta start thinking of alternative moves for some of the things you do. YUP.