Appeltern has labeled its park the 'garden information park', which, I guess, may be a typically Dutch concept. You can walk through a nice collection of show gardens to find ideas for your own yard. In addition, there is a library with books on any type of plant or yard you can imagine, a park area to walk in and a shop for buying garden materials and other paraphernalia. They also show garden furniture, outdoor stoves, different types of pavement and fences.
Appeltern is probably a nice place for foreigners to see how the Dutch live and garden.
It's nice to know there is a the rhododendron show garden at Appeltern, as well as a Japanese garden. Both should look beautiful around the time we visit.
You can find more information here; The information is in English but most of the information (prices, lunch options) doesn't pertain to you as this is already taken care of. The video on the English home page doesn't work but you can always just look at the images, outdated as they may be.