Divide tulip bulbs every three to five years. When you notice that the stems are shorter and the blooms are smaller and fewer, dig up and divide the clump of bulbs. Divide the bulbs in mid-summer, after the tulips' foliage has turned yellow and withers.
After you dig and up remove the bulbs from the soil, cut the growth from the top of the bulb. Separate the clump and replant them immediately.
Dividing tulip bulbs is not required. Decreased blooming may be suitable for your landscape, according to Ron Smith, a horticulturist at North Dakota State. He maintains tulips that were planted 20 years ago; many have never been dug up or divided, but the look is adequate for their purpose in his yard.