From Ground: Before you even think about removing the yellow horned poppy, be sure to water the plant well to help loosen the soil. Use a shovel or spade to dig a circle around the plant to ensure the plant's root ball remains intact. Gently work the spade under the root ball, then carefully lift the plant from its original location.
From Pot: If your yellow horned poppy is potted, watering the plant before the removal can ease the process. Turn the pot upside down while holding the top of the soil, and shake the pot gently. The yellow horned poppy should slide out. In case if the plant seems tight, tap the sides and the bottom of the pot with your hand.
From Seedling Tray: If the yellow horned poppy is still a seedling in a tray, be gentle and slow. Using a dibber or similar tool, push it into the grow medium below the seedling. Push the seedling from below, so it gently pops out of its cell. Always handle seedlings by their leaves, not the stem.