Yeah, I know this sounds super boring, but to someone who is trying to get a handle on what's growing in your garden, its a must. I know personally that my brain can only handle so much and I often forget that I have planted certain things. A plant database is also helpful when people come over to look at your garden and want to know the name of each plant. This is a chance for you to appear as a super genius for knowing the scientific names for your plants.
I'm going through this process right now, myself. Its easier to identify a cultivar and variety of a plant when its in full bloom and at its maximum height. If I look through a few good plant databases online, I then have enough information to find what I need.
A few good resources I like to use are:
Dave's Garden - PlantFiles - Non-subscribers are limited to 10 searches per day, but I love the details provided and the great pictures. The feedback from contributors is helpful also. If you subscribe, then you have access to an unlimited amount of searches.
USDA - Plants Database - Great Resource with reliable information that can be broken down by states. It also includes Canada U.S territories, France and Denmark. Printable Fact Sheets and Plant guides are available if you want to create a binder for your garden
The Plant Encyclopedia - This is like the Wikipedia community for plants. Its goal is to collect plant information from around the world. There are already 300,000 plants listed.
There are many others that are state specific, so I'm sure you can find what you need.
**Word of Caution - If you google a plant, be wary of what pops up as reliable. Its better to use information from a university, government agency or other research based guide. You just don't know what you're going to get otherwise.
To make your plant database shine:
Don't be intimidated that you can't get all of the information, but build it as you go. Now is a great time to start. There is plenty to keep you busy. You will thank yourself later.