From Ground: First, water the dahlia 'Preference' plant to dampen the soil. Then, dig a wide trench around the plant using a shovel or spade, ensuring the plant's root ball remains intact. Carefully work the spade under the root ball to lift the plant from its original location.
From Pot: Water the dahlia 'Preference' plant thoroughly, then gently turn the pot upside down while holding the base of the plant. Tap the bottom of the pot to release the root ball. If necessary, loosen the edges with a hand trowel.
From Seedling Tray: Water the seedlings and then gently ease each dahlia 'Preference' seedling out with a hand trowel or your fingers. Be careful to retain as much soil around the roots as possible to avoid transplant shock.