Watering your plants at night is a great time, especially during hot summer months when the sun can dry up the plant or flowers you just watered. This is even true for indoor plants that are placed near a sunny window. Watering at night requires less watering and helps conserve water.
Gather your water during the afternoon so it will be room temperature when you go to water you plants at night. If your water is fluorinated, as many city water sources are, sit the water out starting the night before. This may not be possible or convenient if your plants are in an outdoor garden.
Water your plants according to their needs. Most plants need soil that is kept moist. Examples of plants that need moist soil include ferns and lilies. Other plants can dry out between waterings (e.g. hoyas), while others only need to brwatered on occasion (e.g. cacti). Remember, over-watering can lead to root rot and other problems.
Water at the base of your indoor plants, if possible. Also water your plants slowly. Don't dump the water all at once. Allow it to soak in slowly as you water. You are less likely to over-water this way because you can stop watering once you notice it coming out the bottom, but if you've already dumped all the water in, it's too late.
Water outdoor plants at the bottom with a hose. Use the spray setting or a rain nozzle if possible and like indoor plants, don't water the plants too fast.
Use a sprinkler at night instead of a hose, if desired. Set your sprinkler so the water spread is wide on full power or decrease the pressure if the water spread is narrow. Since you're watering at night, don't forget to turn it off before you go to bed. Generally, you should water your outdoor plants about an inch to an inch-and-a-half deep. To determine this, you may want to set some containers out to measure how much you are watering and how long it takes. Do this once and you have a good idea of how long to turn your sprinkler on (using the same settings) for the rest of the season.