Here's a thought that crossed my mind...
Modern calendars don't show much more than the days of the week and sometimes the new and full moons and the major holidays (e.g., Easter).
In medieval times, a calendar wasn't just a way of keeping track of time, the later medieval calendars were populated by almost-daily events and personages from the past. Saints days/feast days/days of fasting, days of prayer, (some also included the names of rulers, since they were perceived as demi-gods), etc. In the later 15th century, elaborate floral borders were added to many calendars (especially in France/Flanders).
But even though many follow the same format, they did, nevertheless, come in many different styles. Here are some examples...
This early medieval calendar (Cotton Tiberius A III) is very plain:
This very ornate Georgian calendar is in the Greek style (which was also adapted into Armenian and Latin calendars, but which is especially associated with Greek):
This early 14th-century French/Flanders calendar, in Latin and French, is more ornate than most of them, but it's a good example of all the names that show up in calendars (St. John, St. Stephen, Paul the Hermit, etc.). Notice also that it shows calendar days (31 days in January) and lunar days (in this case 30 for January). The imagery in the lower right is related to month's labors (January is frequently illustrated to tell the reader to stay in, stay warm, eat, and keep yourself alive until winter passes):
A variation on the above calendar is one with zodiac figures, but they are less common than the ones with no pictures or those only with month's labors.
For something less conventional and more visual, somewhat reminiscent of the style of "month's labors" calendars except that they are all on one folio, there is this Ottonian calendar from Germany in Latin and Greek:
So even though most were modeled somewhat the same (the most common being a page or two for each month with lists of names/events next to each day of the month), there were no hard-and-fast rules about how a calendar had to be organized.
So here's a question...
Could a subset of the plants in the VMS (I'm thinking specifically the big plants and mostly the fanciful ones) represent a visual calendar? A way of expressing something about the most important holy days that was maybe tied in with what they believed about plants?