What is the spring holiday celebrated by Wiccans?

I believe that you are talking about Ostara, the vernal equinox. Ostara is a pagan festival and is believed to be the origin of Easter, the same way that Samhain was the origin of Halloween. Wiccans dedicate this festival to the goddess Eostre (Goddess of Fertility). Wiccans pull up flowers and dance around in a circle. They eat "vegetables, dairy foods, pumpkins, sprouts, and certain flower dishes". The special flowers/herbs that they use are "Daffodils, Jonquils, Woodruff, Violets, Gorse, Olives, Peonies, Irises, Narcissus, and various other spring flowers." They use special flower incenses, especially Jasmine, Rose, and Strawberry incense. Many Wiccans also start a Magickal herb garden, or they talk long walks as they reflect on the beauty of Mother Nature.