Another concern with trying to landscape around goats regards the herbicides, fertilizers and pesticides that may be required for optimum growth of these plants. Certain products will pose as much a danger if not more, to the health of the goat. And while a one-time spraying may appear to not be of concern, consider that many of these products will leech into the soil and create a potential hazard within the vicinity.
The age of the goat will also be a factor in determining plants that can be used in landscaping. Older goats that have formed memory triggers will certainly have a better instincts as to which plants they can browse and which they find less of an attraction or taste for. Younger goats however, are still in the process of forming memory triggers and tastes, and may prove to sample a large variety of your landscape before they learn.
In my opinion, the person wanting to landscape is going to have better results if trees are used instead of flowers. The young trees will need to be sectioned off and protected from the goats until they achieve height - the tallest goat should not be able to reach the lowest limbs and leaves of the tree. Also, certain trees are more susceptible to the bark being eaten or rubbed. Softer wood trees especially. Bark eating can usually be eliminated by providing adequate vitamin and mineral nutrition as well as the addition of a "head scratching post" for goats who engage in that behavior. Keep in mind that certain trees are also listed in the poisonous plants section and must be planted with care to avoid potential poisoning hazards.
In regard to Russian Knapweed, I've gone over this with several extension agents that claim that goats will control it. I have not found this to be true for the most part. But let's look a little closer at the situation as it may give insight not only to Russian Knapweed, but other plants as well.
First of all, most plants basically grow in three or four stages; germination, sprouting to flowering/seed, flowering/seeding, full maturity to withering away (most plants). After discussing Russian Knapweed with agents, it was explained that many goats will eat the knapweeds in the early stages, but not in the flowering/seeding stages to maturity because it has become too bitter. They certainly won't eat it in its dried, withered state either.
But my findings were quite different in that the goats wouldn't touch the knapweeds at any stage of life - more than likely because they were being fed other hays and grains. The very next year, I didn't offer very much hay or grains and while the goats ate a small amount of knapweed, they spent more time at the fence line sounding like a herd of hungry goats. So this is something to keep in mind with any plants. If your goats are receiving an adequate diet,thy will shy away from plants that they don't like. But for those plants they have a liking for, good luck keeping them away.
I would strongly suggest planning well ahead before attempting to garden or landscape, paying close attention to all the possibilities I have listed within this article. Overall it will save you time, money and the lessen the risk of an ill or dead goat. As I research this subject and receive more data from other goat owners, I will update this article from time to time.