When using dowels, select a size half the thickness of the wood being joined. For example, for 3/4-in. stock, consider 3/8-in. dowels.; for 7/8-in. stock use 7/16-in. dowels. The length inserted should generally be three times its thickness. Thus, a 3/8-in. dowel should be about 2-1/2 in. long to penetrate into each member 1-1/4 in.
Making separate holes is time-consuming, so an easy way to plant a large area is to remove the top layer of soil to the appropriate depth, add low nitrogen fertilizer according to package directions, set the bulbs in place, and then cover the area with soil. For a natural look, some gardeners gently toss the bulbs in and plant them where they land.