Tulip bulbs, also known as modified roots, follow their own rules when it comes to growing. Unlike other flowers that will start to bloom as the days lengthen with the coming of spring, tulips will only start to flower when they are ready. Tulips also don’t like the heat given off by too much direct sunlight and usually won’t grow successfully unless the bulb is planted more than 8 inches deep in the soil.
The ideal temperature to grow tulips is below 55 degrees Fahrenheit. But there is such a thing as too cold for tulips: The plant has a temperature tolerance limit of 29 degrees. A few degrees below this level will destroy the tulip buds and flowers. If it reaches freezing, the whole tulip can be damaged. Tulips begin to show signs of growth at 60 degrees. Flowers and leaves start to appear at 68 degrees. Because of these precise needs, tulip breeders tend to refrigerate the bulbs so that they can plant them at the right time. In fact, tulips can be planted as late as early December and still enjoy spring blooms.
Commercial tulip growers provide ideal conditions by digging up and storing bulbs in refrigeration. After the spring bloom — and for many tulips, this means late spring — there usually isn't enough time for foliage to manufacture and store food before the days heat up and send bulbs into dormancy. Tulips grow so well in the Netherlands due to the northerly latitude and chilly sea air that brings longer, cooler springs. In most home gardens, there is no guarantee that cool weather will last long enough for tulips to get the growing conditions they need.
