I had the same thing happen with the Magic Fruit Tree quest. I got Gems just for collecting from it.
I read through the questline (I'm also on Outdoor Abode and have the Skunkhouse) and I only see we have to collect from it once for the 20Gems reward and then 2x at the end to finish things out.
I think it's pretty awesome since I originally picked it up at sale price and I am now getting further discounts