Water.
Water is important in the plant's ability to make and move nutrients.
Without water or with too much water, a plant dies. For this reason, watering
is an important part of plant care. Most plants like to be watered when
the soil is slightly dry to the touch. When watering, moisten the soil
by using enough water so that it starts to come out of the hole in the
bottom. (This is why it is important to use containers with drainage holes.)
How often you water depends on a lot of things. Plant size, time of the
year, and type of plant are a few. Your best guide, though, is to feel
the soil. If you stick your finger one inch into the soil and it is dry,
then water your plant.