Bulb is an encompassing term to describe a range of underground structural systems in which plant DNA and nutrients are stored. There are true bulbs, corms, tubers, rhizomes and fleshy roots and all come in a range of shapes and sizes. What most bulbs and bulb-like structures share are both obvious and subtle cues to orient the placement of the bulb in the soil.
Inspect the bulb structure and note the differentiations on all sides. Bulbs are not identical on the top and bottom and not all are symmetrical from side to side or top to bottom. Look to see where the weight or bulk of the bulb rests as the bottom tends to carry slightly more volume or weight than the top.
Identify what is considered to be the bottom of the bulb by looking for a flat or just slightly flattened surface when compared to the other angles on the bulb. A slightly roughened surface texture or even tiny dried root material may be visible. Rhizomes and fleshy root structures can have downward facing root like fingers.
Distinguish what is the top of the bulb by looking for a slightly rounded to pronounced slope or mountaintop shape that tapers in to a point. The sloping tops can be rounded and smooth and covered over with a papery film like gladiolus corms. Alternatively there can be a break in the skin at the point as with amaryllis bulbs.
Orient tubers and rhizomes in the soil by looking for eyes much like a potatoes have that dot the top surface of the bulb from which woody and herbaceous stems will grow. Look for darker or lighter spots than the surrounding tissues that can be raised up or flush with the surface. They can also have small woody or dried tissue stem structures sprouting upwards from them.
Plant bulbs root side facing directly down in the soil and the point or crown facing up towards the sun. Bury each bulb at it s own recommended planting depth which can vary widely.
Provide bulbs a planting bed of well tilled and nutrient rich soil and cover over the bulb compacting the soil lightly. Water in well and cover with several inches of organic mulch if planting in the fall or winter to protect the bulb from cold, drought and soil heaving.