How tall do snow peas grow and do they need to be staked?
There are many different varieties of Snow Peas, and the maturity size may vary between them.
The Peas don't necessarily need a trellis, but the pods are much easier to pick if they are upright and off of the ground.
You can use a trellis or stakes, netting, string and chicken wire to name a few ideas.
Here is a link with more information.