It is sometimes hard to tell if plants are being watered too much by looking. Signs include:
- Lack of growth, particular if weather is warm and conducive to growth.
- Green moss or algae growing on top of the compost.
- A very heavy pot (if your pots are small enough, lifting them is a very handy way to test if they need watering, you quickly notice the difference in weight.)
- Compost that smells a little putrid.
Another thing that may sound blindingly obvious but it took me years to work out is: larger plants need watering a lot more than small plants… So a baby plant in a large pot will usually only need watering every few days, perhaps only once a week. While a large plant in a small pot can often need watering once sometimes even twice a day. So as the season progresses and plants get bigger, you need to water more and more (particularly as it gets warmer, too).
The most reliable way to test if plants need watering is to put your finger a few inches into the soil. It should feel damp like a wrung out flannel, not dry or or soggy wet. Clearly this would be a faff to do with every pot every day - but is a good way to learn how fast your plants are drinking the water. After a while you can use your instinct, but even then, testing with your finger is still a good idea from time to time. I’m still often surprised by pots that are much drier (or wetter) than I expected.