Astral travel is an elaborate and excessive way to communicate with spirits, even then it's not even guaranteed.
To begin with, nature spirits are very easy to get a hold of for the most part or at least easy to find, they tend to differ in preferred manner of communication so you should do a bit research on the specific spirit you're interested in communicating with. Then you need to decide who you're going to work with the particular aspects of that spirit to first, get its attention and then second, keep its audience. This can range from offerings--some spirits like flowers or seeds or sometimes food, to activities--an example would be music or nature walks. After you've figured out the initial gaining of their audience you can usually just talk to them, call their name (if suggested or if known) and speak to them.
My best advice is deciding location, you won't find a nature spirit in the middle New York City.