It's easy to forget what our garden looks like throughout the year unless we write it down.
We do most of our pruning, planting, and assessing in the early Spring. The problem is that at that time of the year, we may have forgotten all of the plants we have gathered in the garden. Sometimes, in our desire to urge Spring and Summer on, we'll plant something in a spot where, in fact, some beautiful wildflowers grew.
You can avoid some of the planting and design problems if you maintain a journal where you note each month where, when, and size of perennial plants. This helps you to remember what has grown and will grow in particular locations of your garden. Your garden is not a monolithic thing, it is full of microclimates, which have different growth requirements.
The garden journal is also a place to add information about the specific plants you have included in the garden. Also, you may not where you got your plants from, which may be helpful in choosing plants for the future.
By keeping a garden journal, you will also be able to note where the pests show up, and when they tend to make themselves known. This way you can be proactive in stopping them--hopefully organically--because they can cause too much harm. You can also use your journal to keep track of fertilization applications, quantities, etc, which will help you to predict your garden's needs for the following year.
Keep track of how your garden changes each year. Take pictures and add them to help you remember.
Add information about the weather for each year. Keep track of rainfall, temperature, and other key data to help identify plants that will work best with climate trends.
Finally, use your garden journal as a compendium of ideas and inspiration. When you see gardens you like, make a note of what you like about them and whether you could implement some components into your own garden.
Growing a sensory garden (or any garden) is a journey, not a destination. Enjoy the journey and enjoy the fact that it is always changing. Use a garden journal to help keep track of the ride.