Tulip bulbs produce strong blooms in their first year and then multiply into smaller bulbs, according to Satsop Bulb Farm, a bulb supplier. However, the smaller bulbs usually are too small to produce blooms for several subsequent years.
The National Gardening Association recommends planting a minimum of 100 bulbs for a 12-square-foot garden to achieve a vivid burst of color. Leaving blooms attached after they have faded allows the seeds to spread, which assists the bulb's natural tendency to multiply. Bulbs also multiply more readily when the correct variety is chosen for a particular climate, such as heat-tolerant varieties for warm climates.