Just for your knowledge, the word 'igelkott' should be pronounced like this: http://www.forvo.com/word/igelkott/#sv

are hedgehogs common there?

I always thought igelkott was a porcupine and not a hedgehog. Turns out porcupine is a piggsvin according to google translate. Now I know.

Could this sentence, depending on context, not be accurately translated as "... in my garden"? If you were at home and wanted to show your housemates the animal you found, I think the most idiomatic English usage would be "... in the garden." If you were at work though, telling your coworkers about what happened over the weekend, I think that "... i trädgården" would more more generally understood as "... in my garden [at home]" than "in the garden [in the office courtyard]", though not unambiguously. Is this an accurate interpretation of this sentence and it's meaning?

So, this is actually happened to me, in another Germanic language country, and it confused the heck out of me. I was in Germany, and the family I was with started looking at something under a hedge, and they said to me "Guckmal! Igel..." (which sounds like "eagle"). So, my German being poor, I was thinking "How can there be an eagle under a hedge... it'd have to be a baby." and I look under there and I'm like "That's a hedgehog." and they go "Igel!" SO... ok. This was long before smart phones, so back inside, I get a German-English dictionary... and voila...

Den blåa igelkotten är väldigt snabb!