- Groot - long o (You need two vowels for a long sound because they are followed by a consonant at the end)
- Grot - short o (If you only have one vowel followed by a consonant you get a short sound)
- Grote - long o (If one vowel is followed by a consonant, which is followed by a vowel again you get a long sound)
- Grotten - short o (If one vowel is followed by two consonants you get a short sound)
So following that logic groote = grote since it is the same pronunciation. To make it more obvious:
- Een groot huis, following the addition of an e would make: Het groote huis.
- However, groote becomes grote.
Now with grote you can ask, why get rid of the second o. That's because at some point we decided to leave the second one out. Why? Probably because we are lazy (or efficient, you pick).
Sounds correct to me, have a listen here for another example: http://www.heardutchhere.net/DutchPronunciation.html#S