We often think of watering plants by pouring water over the top of them. Plants, in fact, don’t like this. They need water at their roots, and can be harmed by water on their leaves, since the dampness can invite mold and other diseases.
But wait. Aren’t plants watered in nature by rain falling on top of them? Yes! Plants have evolved to deal with this by developing various strategies for moving water off their leaves and down to their roots. These strategies also work pretty well when the water is coming from a hose, sprinkler, or watering can, rather than from rain.
But this is a case where we can do better than nature. We can water plants directly at their roots, keeping their leaves dry.
It might seem intuitive to do this by watering at the base of the plant’s stem, but that’s not quite what the plant wants. When plants water themselves by moving rain off their leaves and down to their roots, that water doesn’t end up next to the plant’s stem. It falls along a circle defined by the plant’s outermost leaves. That circle is called the drip line.
Pouring water on the ground in a circle that approximates a plant’s drip line is the most efficient way of putting the water where the plant can absorb it.