I have a system for keeping track of what plants I have in my garden.
I have an alphabetical name list in a spreadsheet and a corresponding list of descriptions of the plants in a document.
I started both lists when I bought my home in 2006. There were barely any plants in the yard at the time, so I was starting with basically a blank slate. What few plants were there, I guessed on or made a generic entry for them.
Some might think I have an awful lot of free time on my hands for doing this. It does take some time, but I find that it is really worth it for me in the long run.
My spreadsheet list has tabs for my categories (Annuals, Bulbs, Ferns, Grasses, Peony, Perennial, Shrubs, Succulents, Trees, Vines, Water, Tomatoes, Dead Stuff, etc.) and then each individual worksheet has the plant names in alphabetical order.
For some of my favorite plants (like Peonies), I also included what I paid for each plant.
I can print this list and keep a copy in my car in a 3-ring binder, so when I go shopping, I'm not accidentally buying a plant I already have. I tend towards "collecting", so I try to avoid buying duplicate plants.
My memory isn't what it used to be either, so a list is handy.
My document file is the same list of all my plants but with a description and photo for each plant. Since Excel isn't the best for word processing, this document is done in Word.
It's not perfect information, but it does give me an idea about the plant's general characteristics and what it will hopefully do in the garden.
I take my own photos for the descriptions and since I have been keeping track since 2006, I will often include updated pictures to show how plants have grown over time. It would be WAY too crazy to do for everything. Even my crazy has limits! So I have only done this with the a few of the ornamental trees.
If the plant tag's information is insufficient, I just Google the plant name, read a few descriptions, and take an educated guess.
For the Peonies, I have also added a vague description of their actual planted location in the garden, when they are not blooming they all look alike and totally disappear when sleeping.
In the winter, I peruse my lists and descriptions. I update what I know has died or been removed for whatever reason. It also reminds me where certain plants are and often I will add a comment how a plant has done over time.
Should something ever happen to me that I need to sell my house, at least the future residents will know what's out there and know exactly what they are getting into plant-wise.
Last count there were 865 different plants in the yard. I hope they are plant people!
I do my best to keep the lists current but even I don't know what some things are anymore.
I'm sure there are some things long since dead, but are still on my list.