HLW has made an attempt with their barrel planter kit, its been fairly successful, so there is a potential market out there, but I think one of the major factors has to be an initial interest in trains in general, which has historically been on the decline. So to try and sell trains in the garden to a generation thats never had first hand interaction beyond maybe their kids Thomas or a commuter train is possibly a tough sell. Now that said in years past at the BTS there was always a good representation from the general families that were there out of curiosity or for their kids, and once seeing the trains in the sample garden that they always set up often opened the doors to the hobby.
One thing about these casual participants though, they often are not interested in running a scale Dash9 around scale 20’ diameter curves on a layout based on a scale reproduction of the Illinois Central, they just want to run a cute engine around a loop of track and thats something that the manufacturers are in danger of losing sight of. If they want to grow their market, they have to address the starter set market, because THAT is where the market begins for most poeple. Bachmann is introducing 2 starter sets based on the Davenport, a mining train and a logging train, which I think are definetly a good move, Aristo’s Critter and switcher sets are also a good place to start, but any manufacturer will need to take this market seriously if they want to continue to attract new hobbiests
Advertsing in garden magazines IS a good idea, you dont need to have full page ads to get the message across, but having the occasional garden layout in a magazine would actually be a better way to spread the word, now that said, how many garden railroaders have even considered submitting their layout to a major gardening magazine or even to the smaller local magazines, they like the train magazines, are always looking for submittals, I dont think they will care if the garden is really good and it just happens to have a garden train in it, in fact that would make a good hook for the reader.