I use an app called Garden Manager (for android). I'm using it as a diary and already I found out a few things such as how I could have planted my beans better. I also was able to identify what pests I have because with the diary I had been monitoring the symptoms. I used to think certain problems had been caused by squirrels until I started using the app. It helped me pay better attention to what was going on. If this is what you had in mind for keeping a log of what works/didn't work, this app served those purposes for me. I'll make a better garden next year for sure.

It has a photo diary, and you can enter measurements like how tall the plant is and you can view a graph showing its growth over time. One of the features you asked for might be in it. You can set alarms for different things. I applied Sluggo to an area in my garden, and the packaging says it lasts four weeks. I set an alarm to let me know when the application wears off.

I created an entry for cucumbers and set a time for when I want to plant its seeds in the fall.

I could use Google Calendar for a lot of these things but the app puts it all in one place so you can see everything on one screen. If you don't have android, there should be plenty of gardening apps that work like photo diaries.

For one entry, I can take a photo, enter the width and height, enter the weather that day (it enters it for you based on local weather data), check off some boxes in a drop-down list of what kind of care I gave the plant (watered, weeded, fertilized, thinned, pruned, custom, etc.), the condition of the plant (germinating, blooming, healthy, sick...), and there's a field for comments. The app has backups. The backup is a file in a folder in your phone. I don't know if it backs up photos too or if you need to back up the folder the photos are kept in as well.