This is because cold air falls and will fill a valley area, while hot air rises and will aid in warming the bulbs.
Planting Depth
Spring flowering bulbs should be planted at a depth of two to three times their height, which for most of the larger bulbs such as tulips and daffodils that equates to a planting depth of approximately 8 inches deep. Smaller bulbs will be planted at a depth of three to four inches deep. The planting depth is measured form the base of the bulb, resting on the soil in the hole or trench. For summer flowering bulbs you should consult the specifications on the packaging as summer bulbs have substantially different planting depth requirements.
Daffodils, hyacinths and tulips must be planted with the root plate pointing downward and the top or nose of the bulb pointing upward.
It is recommended that to obtain the best planting that you till the entire bed to loosen the soil to the correct depth.
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