If you actually have a farm and use a real plough, it's traditional to bless the plough right before using it. The date that one would begin using one's plough would be different in different locations. 

Most pagan and heathen groups that celebrate Charming of the Plough on a specific date don't actually use a real plough for anything. Some American Asatru groups celebrate Charming of the Plough on the second day after Twelfth Night, which is January 3rd. Some celebrate it on February 2nd, which is otherwise called Candlemas / Groundhog Day / Imbolc / Imbolg / Brigid's Day. 

Many holidays have alternate dates. When I was creating the Heathen Calendar, I tried to put in everything, so if there were two possible dates both called by the same holiday name, I put in both, designating who celebrates which date. The less common one is identified as "alternate date." Charming of the Plough is listed on Feb. 2nd as the main date and on Jan. 3rd as "alternate date." 

There are alternate dates for Ostara, too. The Heathen Calendar is meant to present when different groups actually celebrate these holidays rather than picking one "correct" one that people "should" use. I did the same thing with the Slavic Calendar, where there is often a slightly different name for the same holiday from each language or cultural group. I put in all of them. 

Some holidays that I included when I sent the manuscripts of the Calendars to the publisher were inadvertently left off. There are two dates when different groups celebrate Loki's Day. American Asatruars celebrate that holiday on April 1st. Northern Pagans celebrate Loki’s Day on the heliacal rising of Sirius. In 2017-18 that will be August 8. It precesses 1 day every 4 years. It will become August 9th in 2019. The August date is celebrated by fewer people so it is considered the alternate date. That date got left off of this year's calendar, possibly due to a delay in turning the date in because I had to research how to calculate it. If we do another calendar next year, it will be included from the beginning.

When I did the math for these two Calendars, I only calculated dates for 2017. The publisher did the Calendars as 16 month calendars rather than 12 month calendars. Some holidays have fixed dates, such as Feb. 2nd for Charming of the Plough. Moveable holidays such as full moons were not calculated for 2018. I will calculate the 2018 holidays for the 2018 Calendars if we publish 2018 calendars. The decision about whether to publish calendars for a second year has not been made by the publisher yet. 

When agricultural holidays become fixed date holidays, like Charming of the Plough, different groups choose different dates. In some parts of the world, one could not plough in January or February because there is snow on the ground. I encourage people who have farms and gardens to align their agricultural holidays with the actual dates of ploughing, harvesting, etc. in their regions. 

Image: 

A printing of the Slavic Calendar and the Heathen Calendar.