How often should I water? This is one of the most common questions new gardeners ask. It sounds like a good question, and on social media, lots of people will supply an answer.
They are all wrong.
Why We Water
Plants need to be able to get enough water through their roots to keep the top green parts growing properly. They are able to do this when they have a good root system and the soil around the roots has enough water in it.
When water is added to soil, it fills the small pore spaces between soil particles and stays there until it runs away, plant roots absorb it, or it evaporates. Over time the soil becomes too dry and roots can no longer find enough water. The garden should be watered before this happens, but how does the gardener know when this critical point is reached?
Rate of Evaporation
To understand watering, it is important to understand evaporation. The rate of evaporation is a term used to describe how quickly water evaporates. Many things affect the rate of evaporation.
- Temperature – evaporation is higher at higher temperatures.
- Type of soil – clay holds lots of water, sand holds very little, and peat moss is somewhere in between.
- Size of pot or container – large pots tend to be deeper, and deeper soil holds water better since evaporation takes place at the surface of the soil.
- Type of container – clay pots are porous and have higher rates of evaporation than plastic pots.
- Humidity – evaporation is slower in humid environments than dry environments.
- Mulch on the soil surface reduces evaporation significantly.
- Wind increases the evaporation rate.
Watering on a Schedule
Everyone wants to water on a regular schedule: once every three days, once a week and so on. This does not work. If you look at the above factors affecting the rate of evaporation, you quickly realize that they change all of the time. Summer is hotter than winter. Spring may be drier or more humid than fall, depending on where you live. Humidity can change daily as different weather systems move through.
Plants also affect the amount of water in soil. Dormant plants remove water more slowly than actively growing ones. Plants that are located close together remove water faster than if they were planted farther apart. A perennial in early spring has few leaves and the amount of water transpired through the leaves is small. By mid summer the same plant is covered with leaves and it is warmer; resulting in high transpiration rates.
I frequently see people on social media asking for a watering schedule, “I just bought a new rose, how often should I water it?” Other people can’t tell you how often to water because they have no information about the factors affecting your rate of evaporation or transpiration. Only you can figure out how often to water.
What Time of Day is Best?
What is best, morning, noon or night? I had a close look at this question in Best Time to Water – Morning, Noon or Evening?
Wilting plants may or may not indicate that it is time to water.
Leaves will wilt if the soil is too dry and roots can’t get enough water for the plant. In this case it is a good idea to water.
If you water too much, the roots die, and the plant can’t get any water, which results in wilting plants. The last thing this plant needs is water.
For more on this topic see Should You Water When Plant Leaves Wilt?
When Should You Water?
The simple and correct answer is, when the soil needs it. It is really that simple.
How do you determine if the soil needs water? Use the finger meter. Stick your finger into the soil a couple of inches, and if it feels dry, water. If it feels moist, don’t water.
This works for house plants, outdoor planters and the garden.
Let me give you a simple example. Newly planted trees should be kept moist all of the time for at least a year. I usually plant in fall, in clay soil which holds water quite well. I also mulch with about eight inches of wood chips. If I water well in late September, I don’t have to water again until next summer. Zone 5 cools down in September, reducing evaporation. The mulch reduces this even more.
How could anyone on the internet tell me when to water?
Water when soil needs it – not on a schedule.
Tips and Tricks for Watering Plants
Here are some more posts about watering plants.