While it is possible to dry lilies in silica gel, the process is not without its challenges. One of the main challenges is that the silica gel must be completely dry before it can be used, otherwise it will absorb moisture from the lilies and cause them to rot. Another challenge is that the silica gel must be at just the right temperature - too hot and it will damage the lilies, too cold and they will take longer to dry.
The best way to ensure success when drying lilies in silica gel is to use a dehydrator. Dehydrators have adjustable temperatures and exposed trays that allow for good airflow, both of which are necessary for successful drying. To start, cut the lily stems down to about 3 inches long and remove any leaves. Next, spread a layer of silica gel on a dehydrator tray (do not use more than 1/2 inch) and place the lily stems on top, making sure they are not touching each other. Turn on the dehydrator to its lowest setting (around 95 degrees Fahrenheit) and let it run until the lilies are dried (this could take anywhere from 12-24 hours).
Once dried, store your lilies in an airtight container until you're ready to use them - they should last for several months this way.