A garden knife is a special tool used for transplanting, weeding, cutting sod or dividing plants. Some garden knives are ruler etched in steel. These types are useful for measuring the depth of soil while planting seeds or bulbs.  Here the fine tip of the blade serves in drawing lines in the soil for planting gauges. There are different types of garden tools each used for specific plantation needs. So, it would help if you were specific about the preferred use before you head to buy a garden knife.