The birthday of the trees, Tu B’Shevat is celebrated on the 15th of Shevat. This can fall between January 16th and February 13th. As a very minor holiday, the no work rules (see this post) do not apply.
Think Earth Day. (In fact, some groups call it the Israeli Arbor Day) A lot of planting happens. Also sometimes people do a Tu B’Shevat seder which is…always a little silly, imo. It sort of imitates a Passover seder. This is something you’ll see most often with a) children’s groups (i.e. Jewish schools) and b) Jews who tend toward the spiritualistic (such as Jews who practice Kabbalah).
The really big thing about this holiday is fruit - this is the time to eat the seven species (wheat, barley, grapes, figs, pomegranates, olives, and dates) which are native to the land of Israel. I also know a number of people who specifically try to find new fruits and try them at this time of year.
Your characters are unlikely to celebrate this holiday unless they’re a) working with kids or b) super into the environment. But if you’ve got a character who falls into the latter category, this is a great holiday to highlight that.
Honestly, this is a minor holiday and doesn’t really deserve a post of its own, but since it falls smack dab in the middle of Hanukkah and Purim, both of which need their own posts, I’m combining it instead with something else.
Rosh Chodesh and the Jewish Calendar
Rosh Chodesh is a holiday that happens multiple times a year. It’s the first day of a Jewish month, and its name, Rosh Chodesh, literally means “head of the month.”
It is celebrated every month except for Tishrei, the very first month of the year, as Rosh Hashanah includes all the Rosh Chodesh stuff and then does more. By the way, Jews count the start of the month as the new moon, so Rosh Chodesh always happens when the moon is at its darkest. (If you want dates, check a calendar!)
This is a very minor holiday. The no work rules do not apply.
Basically, the main observance is prayer - you add a few prayers to morning services, say one quick additional prayer at afternoon/evening services, add a paragraph into grace after meals, and add a quick Torah service to morning prayers if it’s not already a Saturday, Monday, or Thursday (on those days, you change or add to what is read). If it falls on a weekday, it adds 10-15 minutes to morning services and maybe one minute to afternoon/evening services combined. And that’s it. There may be other rituals for super Orthodox Jews, but for Conservative and Reform, that’s literally it.
Some Jewish women’s groups (especially ones involved in Kabbalah), take it as a time to discuss women’s issues and unite as women. After all, the menstrual cycle is commonly linked to the moon.
However, unless your character either a) attends synagogue every day, b) is super Orthodox, or c) is a woman involved in the spiritual side of things, this holiday is barely noticed.