Dig a planting hole before transplanting your cactus from its pot into the ground. Make the planting hole two to three times the volume of the original pot. Use a garden trowel or a shovel depending on the size of the hole.
Mix the displaced soil from the planting hole with an equal measure of coarse sand. Fill the bottom half of the hole with the amended soil.
Put on leather or heavy twill work gloves. Cup your fingers lightly around the base of the cactus. Tilt the pot to slide the cactus out with the soil and root ball intact. Avoid tugging on the cactus during removal.
Crumble away approximately one-third of the soil from around the roots of the cactus. Removing the potting soil encourages the cactus to spread its roots once it is planted in the ground.
Nestle the roots of the cactus into the planting hole. Check to make sure the base of the cactus is even with the surrounding soil and not below it. Add additional soil underneath, if needed.
Hold the cactus upright with one hand. Fill in around the cactus with the amended soil until the roots are buried.
Tamp the soil around the cactus to push out any trapped air. Add soil around the cactus if the soil level is very low after tamping.
Withhold watering for two weeks after transplanting the cactus into the ground. Begin watering with 1 to 2 cups of water every 14 to 20 days after that.