I used to have a hard time not killing plants in my flower, herb, and vegetable gardens. I'd either overwater them or under water them.
Often I thought a recent summer rain had already watered plants for me because the soil was wet on top but not deep down at the root of the plant. The result? Plant murder. (Unintentional, but it's still death.)
A few years ago, I learned a great little gardening hack on how to know when you need to water a garden that works 100% of the time - use a simple rain gage like this one! (Disclosure: I'm including an affiliate link for your convenience.)
I put my rain gage in a pot in my outdoor container garden.