I find that moving wheeled things over rough surfaces can go at least a little easier if you pull rather than push.
I think that's because usually pulling means that I'm pulling and lifting from the front. That helps the front wheels get up and over high spots, or up and out of a low spot. The back wheels are still a problem unless you have helpers and four ropes.
in the case of the dolly, it might help a little to tie heavy rope really solidly to the two leading corners. (Eye bolts? Drill a hole and thread the rope?) rememeber that attaching the rope as far from the center of gravity as possible gives you more leverage.
Maybe add small loops or big knots on the ropes to give a getter grip. That way you can use all of your strength (bend legs, not back!) to pull-and-lift one corner at a time over rough spots.
If the hand-grip is the weakest link, wrap the rope around your forearm and wrist so that your legs and shoulders do more of the work whilew rist and fingers are not involved.
Warning 1: While a good hard tug will get you over most bumps, the lift, tilt and jolt might just tip that plant right off the dolly, ka-boom. Now you can easily roll the broken fragments to the compost heap.
Warning 2: Pulling and lifting does little to help you get through long grass or sand or soft soil. Skids like a sled or a travois might be better than wheels.
Or better, a really really heavy tarp or length of sturdy plywood will drag over grass or sand Use ropes to lift/pull the leading edge of the plywood. Or lay the plywood over the grass and roll the dolly over the plywood.
What is better for heavy lifting and carrying than wheels, skids, sleds, travoises and lift trucks? Beer. It works much better than mechanical advantage.
"John? I have some beer that I don't know what to do with, and several very heavy plants that I need moved. Do you have a few burly, thirsty friends with some free time who would help me solve these dilemmas? "
