Watching a garden grow

I've been watering my friends' garden for the past week while they are out of town. It's still in the early stages of growth. Except for the cayenne peppers which are hitting their prime and the sugar snap peas which have passed their prime. The tomatoes are starting to ripen and other plants are beginning to flower. But gardens are interesting to me, because you wait and wait and wait for things to grow and bloom and produce, then one day you walk outside and....tada! The plants are six inches higher. A week later you go out and...tada! Flowers or fruit or vegetables have appeared. Do we just not notice the growth until it's significant or do the plants grow in bursts. And why do they always grown when we're not looking?