Our green brothers and sisters are not as obvious as our animal relatives, but they are just as informative and helpful. Some people do regularly talk to their plants, or hug trees, but rarely do these same people expect to be talked back to! And, if you are open and attuned to receiving such vibrations, you certainly can hear the small voices of plants, or the Devic energies which inhabit them.
You can learn a great deal by simply placing yourself among plants; say, at a plant shop, hot house, garden, or out in the wilds. Look at them, touch them -- if that's appropriate, some plants are harmful when touched, like Bleeding Hearts. Smell them, admire them, and in general get a sense of the plants identity. Once that's done, sit down as close to the plant as you can get, relax while gazing at the plant, and close your eyes. What body sensations do you get? Where? Do you feel anything at all. Does it seem like you can hear something? IF so, what? Is it high or low pitched? Do any of your senses seem suddenly more predominant than any of the others? Which one? Can you relate this to a feature of the plant?
Relax some more. Do you hear anything, perhaps a low humming, or even a regular pulsing beat? Shift your attention to your imagination and see if you are experiencing any mental images? Are there colors? Shapes? Can you relate this to the plant in any way? Open your eyes and look at the plant again. Greet it, tell you are trying open yourself to communication with plants and would welcome hearing from it in whatever way is best. Then close your eyes, wait, and again pay attention to any input from any of your senses. Don't worry if nothing seems to be happening at first; it will. The fact that you've taken this time to do this preliminary works has opened the doorways between you and plant kingdom. In fact, if you've already found, or been found, by your animal friend and guide, call it in and get it involved in this experiment too!
Remember to be as open and child-like as you can. If you're looking for a tree to stand up and walk over to you, it isn't likely. But if you're open to having your inner site opened so that you can perceive the living energy and personality of the plant, then you'll probably be successful. Sometimes, however, I've heard of people doing this work with a variety of plants for several weeks only to receive nothing in the way of psychic input; then out of the blue, the entire Devic Realm yawned open and nearly overwhelmed the senses. So don't pressure yourself or the plant kingdom, it will happen when and as it should.
As with the other kingdoms, take the time to study and read up about plants. A very good book, one that often turns people's thinking right on its ear, is The Secret Life of Plants by Tompkins and Burns. You might also do a little research into the Findhorn Community; Perelandra, here in the US; and take a look at one or two of Michael Roade's books, which describe his encounters with Pan and other forms in the natural world. The point is, the more knowledge you have in your head, the wider the possibilities for the Otherworld to work with -- since they can only use what you have as storehouses of personal information and knowledge to communicate with you. Of course, you could go too far. You could read so many things that you subconsciously think this communication has to go in a certain way, or it's all wrong. Find a happy medium and then try plant communication. And don't forget that the communication just might take place in your dreams!
For more specific information on herbs go the Garden or to the Cottage. And don't forget, you're on the World wide Net, there are many good sources right here at your finger tips. Over time I will be adding specific herbs and other plants to this page, so do come back and check it out.