Botanicals are merely dried flowers. Many are seasonal in that they are only available at certain times of the year and many have better availability such as the Red Rose Petals which are available year round.
They add another dimension to your soaps in making your soaps look attractive, or with some botanicals such as poppy seeds adding texture.
However, it is important to remember that the main ingredient in Melt and Pour soap bases is WATER.
If you add dried flowers into the soap base, they will absorb the water from the soap base and over time they will turn brown. This is not a problem with the soap but it doesn't look too attractive.
The easiest answer is to add to the top of the soap bar when the soap is just set.
Of course there are exceptions in that Calendula Petals and Blue Poppy Seeds can successfully be incorporated into a bar of soap.
Try adding a single Pink Rose Bud to the top of a bar of soap - looks very elegant and luxurious.