You can grow outside, but it depends on the climate. I’m from the US in a region that’s very well known for being great for growing bud outdoors.
Try looking up outdoor growing for Germany, specifically in the area you live. Not only the weather, but the soil and amount of daylight/ night time they get matters too. During the first part of the grow, your plants need at least 16 hours of sunlight, and at the end during flowering you need as close to 12 hours sunlight and 12 hours dark as possible.