While purchasing new grapevines from a garden center or nursery is one way to increase your stock, another, more affordable way is to take cuttings from your existing grapevine and plant them so they become their own vine. Take your cuttings in winter, from November to February, during the plant's dormant stage. In just a few steps you can root grapevine cuttings and have new plants ready within a year.
Dig an 8 to 10-inch-deep trench with a hoe in well-draining soil with full sun. Make your trench resemble a "V" shape with one edge of the V running vertically up and down to form a back wall. Add sand to the bottom 3 inches of the trench.
Cut pencil-thick stems from the grapevine with sharp, clean pruners. Each cutting should have three or four buds on it. Cut on a diagonal away from the bud. Make the cuts just before a bud along the base of the cutting and just after a bud at the tip of the cutting. Make each cutting 9 to 12 inches long.
Hold a cutting upright and dip the bottom of it 1/2 inch into water to wet the base. Dip the cutting into the hormone compound while the end is still wet and immediately set the cutting into the trench with the treated end pushed lightly into the sand.
Repeat Step 3 until all of the cuttings you have collected have been dipped and inserted into the trench. Space each cutting 4 to 5 inches apart.
Fill in the trench by hand by gently moving displaced soil back into the trench. Be careful not to knock any of the cuttings over. Fill the trench until the only thing sticking up from the soil is the top 1 inch of the cutting with the bud on the tip.
Press around each cutting to pack the soil and secure their position. Water weekly as needed so the cuttings don't dry out. Allow the cuttings to grow for a year in this spot before moving them to a permanent location.