From Ground: First, water the american plum plant to dampen the soil. Then, agitate the soil around the plant using a garden fork, being careful of the root ball. Dig a wide trench around the plant with a shovel or spade; try to keep the root ball intact. Carefully work the spade under the root ball to lift the plant from its original location.
From Pot: Water the american plum to soften the soil. Invert the pot while holding the american plum at the base and gently sway it to detach the plant and root ball from the pot. For stubborn plants, you might use a trowel to help guide the plant out.
From Seedling Tray: Depress the soil around the american plum seedling using a slim object like a pencil. Gently lift it, taking care to hold the leaf and not the stem to avoid damage. Remember to maintain the integrity of the root ball during the process.