Watering tomatoes: How much and how often should you water tomato plants

Full grown mature tomato plants can easily use 2-3 gallons of water daily, sometimes more. Some may use 4-5 gallons daily. How do I know this?  I make and use SelfWatering containers and pots. The containers/pots have a water reservoir in the bottom holding 3-4 gallons of water. During peak season bigger plants can run out of water within a couple days.  

Using the suggested potting mix/soil will keep the soil moist but not soggy ... these soils contain lots of sphagnum peat moss. One pound of sphagnum peat moss can hold up to 25 pounds of water.  When using great potting soil you save on water and you don’t need to water as often either—you save water.

What is the Best Time of Day to Water?

Water in the mornings if you can—this way any excess water on the leaves or surface on the soil will evaporate quickly with the morning sunshine. Evening watering will leave the surface soil wet too long inviting disease.

Avoid getting water on the leaves

Also, prevent lawn sprinklers from spraying water or misting on the tomato leaves.

Too much water on the leaves invites disease and your plants will become diseased. If you must get water on the leaves, do it during the day when it will quickly dry.

Where does all this water go? 80-90% of the 2-3 gallons of water taken in through the roots is used by the plant to transport minerals, nutrients and food including your fertilizer throughout the plant. Some evaporates from the soil. After delivering the nutrients, most of the water eventually evaporates as water vapor through the leaves.

How to water your tomatoes in pots, containers

When watering tomatoes in your pots, containers, etc—slow water until water comes out the overflow hole on Self-Watering Containers or out the bottom drain hole on regular containers. The water reservoir in Self-Watering Containers holds about 3-4 gallons of water.

Containers hold about 4 gallons of water. 

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water pouring out of drain hole of self watering container

Self Watering container: put the hose down the fill pipe until water runs out the overflow hole.

Do you need a moisture meter?

Everyone should have a moisture meter.  They cost about $10.  Buy online or big box stores, plant nurseries. 

Above, a simple moisture meter with a 6 inch probe down into the soil that tells you when to water.  There are 3 zones on the meter. Dry, Moist, Wet. Simple enough. When it gets close to the Red Dry, time to water. Remember, when using great potting soil you cannot over water.  

Gently water without washing away the soil

Fill deep water pipes a couple times

Then, if you have “deep water” pipes, fill each deep water pipe a couple of times every time you water your tomato plants.  Slow water around the base of the plant then fill the Deep Water Pipes a couple times.

You are welcome to share this information with others—family, friends and clubs, etc.

Sharing tips helps us be better growers.

Dave Freed /  the Tomato Guy