The easiest way to move a heavy urban planter box that is already filled with soil is to avoid lifting it. Soil is dense and awkward, so the goal is to reduce weight if possible, then slide and roll the planter instead of carrying it. If you can, remove the top third to half of the soil and any plants first. This alone can make the difference between a two-person job and a dangerous lift. If the planter must stay planted, work in stages and use mechanical help.
Clear a path and protect the surface. Remove loose items, sweep the route, and place plywood or cardboard over delicate decking or tiles. Wear gloves and sturdy shoes. Gather a pry bar or strong lever, several wood blocks, a heavy-duty furniture dolly or hand truck, two or more lengths of PVC pipe or metal pipe, and ratchet straps if the planter has no good grip.
Start by using the pry bar to lift one edge just enough to place a wood block underneath. Do not try to tip the planter far. Work around the base and add blocks until you can slide a furniture dolly or a length of pipe under it. For a large square planter, two people should work together, one on each side, and coordinate the movement. If you use pipe rollers, place two or three pipes under the base and push slowly; as the planter rolls off the back pipe, move that pipe to the front. This is often the easiest method for a very heavy box on a flat, hard surface.
If the planter has casters or a wheeled caddy, make sure they are rated for the filled weight. Many standard plant caddies are not designed for a large soil-filled box. For short moves on smooth concrete, a heavy-duty furniture dolly with straps is usually faster. For rougher surfaces or thresholds, use plywood runners and take it slowly. Never drag a filled planter across a deck without protection, and never lift a large planter by its rim; the rim can crack and the soil can shift suddenly.
Move the planter in small increments, checking the path and keeping hands and feet clear. Once it is in place, remove the dolly or rollers, lower it carefully, and water the plants if the soil has loosened. If the planter is too heavy to tilt safely or the route includes stairs, stop and empty it completely. The easiest way is not the fastest way: reducing weight first, then using a dolly or pipe rollers, is the safest and most practical method.