Watering Tomato Plants

Updated: Jul 27

Watering tomato plants properly is the magic ingredient need to help them to thrive - emphasis on properly. But how much water do tomatoes need, and how often? Lets dive in.

We're going to walk through 3 key things:

  1. What you need to know about watering tomato plants

  2. How often to water tomato plants ; and

  3. How much water do tomatoes need?

Fun right? Although if you're anything like me, I'm guessing you'd rather be playing in the garden than reading about watering it, so lets get to it! :)

What you need to know about watering tomato plants:

First, the why. Watering and irrigation lets Tomato plants 'transpire', which is when water moves up the plant stem, from root to leaf. It's to plants what a heartbeat is to humans.

This is important for 4 reasons:

  1. It helps your tomato plant draw up essential nutrients from the soil, and distributes these nutrients throughout the plant.

  2. The water that moves through the plant to the leaves (as a result of transpiration) contains essential minerals that aid photosynthesis.

  3. It also helps to keep your tomato plant cool if necessary since water evaporates through the pores of the plant. It's a bit like when people sweat.

  4. Lastly, If you’ve ever had a plant look droopy, then noticed it perked up after watering it, then you've seen another important effect of transpiration: M\maintaining water pressure in the plants cells to support the plant.

Next up, when it comes to what you need to know about watering tomato plants is when.

Watering tomato plants when they're seeds:

To ensure there’s a good seed-to-mix contact, I find it helpful to water them after seeding. Whenever possible, use a plant mister or just slowly drip a light stream of water over the top.

You don’t need to drench the ‘soil,’ just dampen the top layer. If you don't have a mister yet, they're awesome since it dampens the seeding mix without disturbing the surface or the seed. Mines' just from the dollar store, but you can also get prettier ones online or at your local garden center.

Continue to keep the soil moist but not saturated. Since dry seed-starting mix usually turns a lighter color when it dries out, so when you see this, it’s a good indication that your sprouting tomato babies need water.

Watering tomato plants when they're seedlings:

Watering tomato plant seedlings from below makes it easier to avoid disturbing the seeds, or compacting your soil (which typically happens when you water them from above).

To water from below, rest your sprouting tray or containers onto a tray of water, but don’t let the water go above the top of the planter, as the goal is to simply allow the soil and roots to absorb the water they need through the drainage holes at the bottom of your container. Leave it to soak the soil for a couple hours and then remove any left over water.

If watering from below your tomato seedling isn’t possible, use a mister to dampen the soil rather than directly pour water onto the surface. Yup, we're back at the mister. They really are awesome!

Watering tomato plants while growing and producing fruits

Are you thinking "Yes, can I now finally just dump some water on them for the win?". You can, but your tomato plants will thank you if you keep watering low. If your tomato plants are in containers, try watering form the bottom. The reason I don't recommend watering from the top is because most people end up doing what's called shallow watering – a little bit of water given fairly often. Plus getting your leaves wet in the hot summer sun can lead to all sorts of challenges. So even if you need to water from above, try to do so close to the soil to avoid as much of the leaves as possible.

The challenge with you watering tomato plants a little and often, only the top layer of soil tends to gets damp, and the water never makes it down into the deep-rooted area of the soil. This discourages roots from getting strong and diving more deeply into the soil, which isn't ideal, plus keeping the top layer of soil damp also creates an ideal environment for harmful bacteria and fungi to grow – ummm, no thanks!

On the other end of the watering spectrum is deep watering. You're going to make your tomato plants VERY happy with this method.

Deep watering is the process of saturating a plant’s root system, so that it can hold enough water to fuel itself for a while. The key to deep watering is to saturate, but not over-water.

This can feel intimidating at first. Many of us will have lost plants to over-watering in the past, and as a result we may be cautious. It is a fine line, but don’t worry – we are here to walk you through it and make sure you avoid drowning your plants!

For deep watering, we suggest soaking the soil to a depth of at least eight inches beneath the surface. The key to effective deep watering is to pour your water slow and deep. If your water flow is too quick, the soil won’t have enough time to absorb the moisture, and the water may run right through it, missing the roots completely.

The best way to care for your leafy friends is to take your time, and to pour the water slow and steady. If you are using a sprinkler system, usually a half-hour or so does the trick nicely.

To avoid over-watering and plant death-by-drowning, we recommend that you deep water your plants only once a week, unless you are experiencing a drought and/or significant heat (remember that transpiration helps to keep your plant cool if it’s hot).

I love this watering method because it encourages tomato plants to develop deep and strong root systems, and strong roots are a gardener’s dream!

How Often to Water Tomato Plants and how often do tomatoes need watering?

Now that you know what you need to know about watering tomato plants, next up is how often to water tomato plants.

How often? Trick question! I've always found that it's less about frequency and more about moisture level. For example, although I could tell you that most tomato plants need on average at least a quarter inch of rainfall consistently every other day (the equivalent of a light rain for 2-3 hours, or a moderate amount of rain for 30-60 minutes.) That's not going to really help you. So if it's been over 75 degrees outside, you'll want to double that amount of water. Then throw in different kinds of soil, and it just get messy and needlessly confusing really fast. So lets keep it simple. First, lets talk about the right amount of moisture, and how to help keep that watering consistent and save some water along the way.

For starters, I find a cup of water each day per square foot of soil does the trick. Two cups if it's extra hot. If you can get a moisture reader (they're usually about $20 at your local garden center), tomatoes love a moisture rating of 60-80 depending on your soil type. Don't worry about the details, just land somewhere in there and nature tends to take care of the rest. Gardening should be fun, so good enough is...well...good enough when it comes to this topic.

If your soil is a 60 or an 80 is less important than watering consistently. Let me give two examples of why that is.

1) Have you ever had cracked tomatoes? Inconsistent watering is likely the culprit. Irregular watering—missing a week and trying to make up for it—leads to blossom end rot and cracking. Inconsistent watering exposes your tomato plants to rushes of water and can pop the skin of a ripening tomato, much like an overfilled water balloon.

  • Solution: Instead of a quick sprinkle every day, try watering deeply once or twice a week (depending on rainfall), twice as much if its extremely hot out. Mulching is also a big help because it keeps moisture from evaporating...but I'll get to that in a bit.

2) Have you ever found tomatoes with a soft of rotten spot while growing? This is usually a sign of a calcium deficiency and is often caused by uneven watering. Frequently going between wet and dry soil can interfere with your tomato plants’ abilities to use calcium.

Mulching is a great way to help your soil retain water and increase room for aeration if you lightly mix it with your topsoil that's around the base of the plant. Mulching can significantly reduce the rate of water that evaporates from the soil. With mulching I find that if I was previously watering tomatoes twice a day (or more), I can usually go down to watering once daily—that sounds like a win to me, and my water bill.

Water Tomato Plants, and...

...so much more. To discover everything else you need to know about growing tomatoes from seed to harvest, check-out the full step by step guide: Watch the animated video, read the transcript or download the PDF for later. Your garden, your choice. :)

Topics covered in those include:

Tomato Seeds

• How to select the suitable tomato varieties for your situation

• Avoiding disease in tomato plants

• Starting your Tomato seeds

• Preparing containers and your growing medium

• How to plant your seeds

Tomato Seedlings

• Growing strong seedlings

• Useful tips

• Moving growing seedlings to bigger pots

• To fertilize or not

• Thinning your seedlings

• Transplanting tomatoes outside

Supporting Tomato plant growth

• Support structures

• Pruning

• Feeding & fertilizing tomatoes

• Mulching

Common tomato plant problems and solutions

Harvesting and storing tomatoes

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