When you want to grow grapes in your garden, there must be somewhere for them to grow vertically. While a wall or existing fence might do the trick, you'll have more luck and a higher yield if you build an actual trellis or "fence" for the grapes. The structures typically include sturdy posts at the end of each row, with strong wires stretched in between. While some grape growers opt to add more than one row of wire, a single wire stretched between posts is typically adequate for home gardeners.
Drill a pilot hole along the side of each 8-foot post, about 2 inches from the top of the post. If you are building a grape trellis with two or three sets of wires, drill another hole into each post about 12 inches below the first, and then a third hole -- if you're using three wires -- another 12 inches below that.
Insert 1/2-inch eye screws -- also called eye lags -- into each hole and turn them to tighten them as much as possible, stopping when the holes are facing to the side. Posts will be placed every 16 to 24 feet, so if you're using more than two posts, you'll need to insert two sets of eye screws on the middle posts, on opposite sides of the posts.
Dig 2-foot-deep holes every 16 to 24 feet along the length of the area you want to fence.
Place your posts into the holes with the screw eyes facing inward toward the center of the trellis -- or shooting out from each side if you're using more than two posts -- and then fill the rest of the hole with quick-setting concrete. Pour enough water to completely fill the hole and allow it to dry. While it's drying, hold a level against each post to ensure it's staying level, and nail 2-by-4-foot boards against the posts, resting on the ground, to hold the posts in place as they dry.
Use a wire cutter to cut a piece of 12-gauge wire to a length that is about 6 feet longer than the distance between your posts.
Wrap the wire around the end of one eye screw, leaving about 3 feet of wire as excess along the end of the wire. Pull the long portion of the wire to remove the slack, hold it in place on the eye bolt, and then twist the 3 feet of wire around the long end of the wire tightly.
Pull the wire tightly and wrap the free end of the wire around the eye screw on the opposite post. Then twist the 3 feet of wire left on the end around the taut, long end of the wire. If you're using more than one set of wire, repeat this process for all lengths of wires and eye bolts.
Stick T-style metal fence posts into the ground about every 6 to 8 feet in between each wooden post, driving the pointy end into the ground. If your ground is very hard, you may have to dig holes with your post hole digger before inserting the pointy end of the posts into the ground.
Slide the wires over the top of one of the hooked lips on the metal fence posts, providing more stability for the wire.