I would not recommend planting them in ground because they like acidic soil, don’t like city water and hate cold weather. Unless you have a long term plan to keep them warm and acidify your soil and water, it is going to be a difficult and often short road.
Even when grown in pots and moved indoors during cold weather, many people have difficulties growing this plant and keeping it alive for more than a couple years.
Seedlings grow very slowly, especially for the first year or two. I have not tried to direct seed miracle fruit into the ground. I would assume that they will probably succumb to the cold weather at my location since I get a bit of frost almost every year.
Like Finca la isla said, you may want to try air layered plants. I order my plants from Plantogram.com
Simon