Plant one butternut squash seedling per square foot, utilizing the squares on the trellis side of the garden bed. Plant the seedlings at the same depth they were growing at in their seedling pots.
Water the plants one to two times weekly so the squash receives approximately 1 inch of moisture per week. Keeping the soil moist to a depth of 6 inches is sufficient.
Guide the squash vines onto the trellis netting once they are long enough to reach. Butternut squash vines primarily climb the trellis on their own, but tying the heavier vines in place loosely with a cloth plant tie makes the plant more secure.
Pinch the top of the vine off once it reaches the top of the trellis. Alternatively, guide the vine down the back side of the trellis, using plant ties to secure it in place.
Cut 1-foot-long strips from old T-shirts or other somewhat stretchy material. Tie the ends of the fabric strips to the trellis directly below each developing butternut squash so they form a sling. Place the squash inside the sling to support the fruit's weight as it grows.
Harvest the squash from the vine once it's mature. Butternut squash develops a hard rind and an even pale orange or light tan color when ripe.