We are nearing Ostara and a symbol that is everywhere at this time of year is the humble EGG. The egg is a powerful magical symbol that is associated with new life, fertility and the cycle of birth, life, death and rebirth. We often associate the egg with the Springtime of year because this is when new life is starting to birth through whether they are animal or plant-life. In the very early decades and centuries of Christianity the Egg is a symbol that marked Lent is coming to an end, but there is also a tradition that relates to Mary Magdalene telling the Roman Emperor that Jesus would be resurrected, and he said it was more likely a nearby bowl of eggs would turn red, so some Christians use red eggs at this time of year as a symbol of this resurrection.
The use of eggs around Spring time can be found in many different cultures from all over the world from Persia, to China to the Native Americans and many places in between, here are a few examples:
In the Ukraine eggs are covered in Wax and decorated to honor the Sun god.
In the Native American traditions a giant egg was cracked to form the Universe.
In China the god Pan GU was formed inside an egg and during his attempts to escape the egg cracked in two, the upper side become the cosmos, the lower half became the earth
In Persia eggs are painted to celebrate No Ruz which coincides with the Zoroastrian New Year
You can use eggs as a symbol for fertility in many different kinds of spells, be it a fertility of the mind, or fertility of trying to have a child. You can use the egg symbol all year round, it is not exclusively associated with Ostara. You can use Eggs in fertility rites around Beltane too.
If you are creating an altar for Ostara you don’t have to use any specific kind of eggs, you don’t have to use real eggs. You can use crystal eggs, I have a set of brightly colored foam eggs, you can get polystyrene eggs and decorate them. I have also seen wooden eggs around as well, which can open a vast array of designs.