Germany in March

If you mean the weather, it would concern me, too. You can explore day-by-day actual historical weather data on wunderground.com. Enter one of your major destinations, choose History > Monthly, then select March 2018 from the pull down boxes. Repeat for March 2017, March 2016, etc.

Germany is a big country - weather varies a lot from east to west, north to south, and elevation plays a part.

Where in Germany?

Starting in Dortmund to see a soccer match then heading south to Cologne, Munich regions

My response is based on travel during the first 2 weeks of March 1990. During that time, we traveled from Frankfurt south through Bavaria and down into Geneva Switzerland. We did not see any snow nor was our vehicle equipped with snow tires as is mandated in Germany in the winter months. We saw sun and rain and weather that would be described as chilly to me or cold to my wife. My recommendation is to have waterproof comfortable walking shoes and a 3 in 1 jacket that is waterproof. I would travel again at that time of year. However, Since then our travels to Europe have been in mid to late September or November/December. Pay attention to the weather and plan accordingly. You can add some of the cities to your phones weather report and keep a daily watch if you like. I currently have Frankfurt, Prague, & Budapest on mine.

I’ve been to Scotland, Ireland and Italy in March and had no rain at all, surprisingly. Go for it! Be prepared for cold, wet weather with layered clothing. If driving in snow is a concern, take the train. It probably isn’t an issue in the north, but if you want to go to the Garmisch area it could be an issue. The hours for sights might be shorter than peak season, just plan accordingly.

I’ve been to Scotland, Ireland and Italy in March and had no rain at all, surprisingly. Go for it! Be prepared for cold, wet weather with layered clothing. If driving in snow is a concern, take the train. It probably isn’t an issue in the north, but if you want to go to the Garmisch area it could be an issue. The hours for sights might be shorter than peak season, just plan accordingly. To me, March is the ideal time to travel as long as your expectations are realistic. You won’t be swimming in lakes or sunbathing, but you won’t have the crowds of summer either!

Based on our climate the weather at this time is really unpredictable.

For all mentioned regions in total expect between +25c with first green leaves and -20c with snow thunderstorms. Not ironically meant.

In Germany weather is reliably predictable 3-4 days ahead. Public weather service:
https://www.dwd.de/EN/Home/home_node.html

I suggest also to lookup climate tables in Wikipedia, e.g. Cologne:
https://www.wikiwand.com/en/Cologne#/Climate

Attractions shall be open but look up special opening times. And events are rarely moved due to weather only. In Germany we do not have bad weather, there is only wrong clothing.

We travelled in Vienna, Budapest. Berlin and Munich in March 1- 29, 2017 -- by the end of the first week I was able to peel off the leggings under my jeans. Rain jacket came in handy, with a fleece underneath. Crowds not bad, everything seemed to be open.

I've frequently been to the Frankfurt and the Rhine/Mosel areas in March over the last 40 years and it was NEVER warm, not warm enough for buds, blossoms, biergartens, or bare forearms. It's generally not a great time for biking or other outdoor activities unless you bundle up a bit. Easter (April 21 in 2019) week is a typical time for seasonal attractions to re-open. Because Easter comes so late next year I suspect some places will open a bit earlier, but perhaps not as early as mid-March... but then what really matters are the places YOU intend to visit, and opening dates are fairly simple to look up these days.

On the plus side, cities of some size tend to offer year-round attractions and are often pleasantly free of foreign tourist crowds.

You're a Borussia Dortmund fan? Fantastic ! So am I. Will you wear the yellow?