Watering Tomatoes: How to Do It?

What water should be used to water tomatoes? And in what quantity?

We can’t stress this enough: the best water for watering is rainwater. Stored at room temperature, it doesn’t cause thermal shock to plants.

In theory, we recommend watering tomatoes with 1 litre of water per day. This indicative figure should of course be adjusted according to several factors:

• The growth stage of the plant: water needs increase until fruit formation and then stabilise during ripening. A recently planted tomato plant doesn’t need large quantities of water to develop. Overwatering at this stage could cause rotting or, especially if combined with heavy nitrogen fertiliser application, lead to overly rapid growth making the plant more fragile.
• The climate, outdoor temperatures and cultivation method (in pots, in the ground, outdoors or under cover): the hotter it is, the greater the evaporation and the more your tomatoes will need watering. In greenhouses or polytunnels, temperatures rise very quickly and can easily reach 50°C. In pots, soil temperature can also rise very rapidly.

Under cover, tomatoes are exposed to high temperatures: adjust watering accordingly

• The nature of the soil also has significant influence: clay soils as well as rich, humus-bearing soils retain moisture longer than poorer, sandy, free-draining soils…
• The varieties grown: small-fruited tomatoes like cherry types will need less water for fruit formation compared to large-fruited varieties.

Key points to remember: water moderately, taking into account the size of your young plants, growing conditions and rainfall. Avoid overwatering to encourage the root system to develop deeply. Remember to mulch the soil to retain moisture.

When and how often to water tomatoes?

The best time to water tomatoes is early in the morning. You can also water in the evening, but this is slightly riskier: if the foliage gets wet, it will dry more slowly than during the day, increasing the risk of blight taking hold.

There is only one golden rule when it comes to the frequency of watering: regularity.

Indeed, watering too randomly, inconsistently, too often or not often enough, and in excessive amounts causes water stress, leading to physiological issues such as blossom end rot, fruit splitting, and leaf curling (to learn more about these phenomena, check out our advice sheet “Tomatoes: Blight, Other Diseases and Pests”).

Proper watering doesn’t necessarily mean watering very frequently, but rather at a regular rhythm, which could be every three or four days—or even, in very favourable conditions, every two weeks!

If you grow your tomatoes in pots or containers, the growing medium dries out very quickly, so watering should be even more regular to prevent the compost from drying out completely. Otherwise, you’ll find it much harder to rehydrate.

Key takeaway: water while it’s still cool, choose a schedule and stick to it to avoid stressing your young plants. If this seems complicated, opt for an automatic drip irrigation system.

How to Water Tomatoes Properly?

• The watering can: a classic yet effective method for watering tomatoes

The simplest way is to water your tomatoes manually, using a watering can, gently and carefully to avoid wetting the foliage. To achieve this, don’t hesitate to remove the lower leaves (see our advice sheet «Pruning tomatoes and their cultivation»).

Water using the rose, at the base of the young plant and around it (especially if you planted your tomatoes lying down) so that the entire root system of your tomatoes can benefit from the water.

You can also water directly with a hose, but this method is less practical as you’ll often struggle to gauge the amount of water being distributed.

• Automatic drip irrigation: well-suited for tomatoes

Nothing is more consistent than drip irrigation. This method is therefore perfectly suited to growing tomatoes and even allows you to be away for a few days. Sold in kits and easy to install, these systems connect either:

– to a tap,
– to a water tank placed at height so that gravity provides sufficient pressure.

The only drawback of drip irrigation is that you usually place a single dripper at the base of the young plant. The watering is therefore very localised, which doesn’t encourage the roots to spread underground.

Also read: How to install automatic irrigation on a balcony or terrace?

• The bottle technique and other tips and tricks for watering tomatoes

One of the most well-known tricks is the water bottle method. You can choose between these two variations:

– cut off the bottom, pierce small holes in the cap, turn the bottle upside down and bury it in the soil, then fill it
– pierce small holes in the bottle, bury it in the soil and fill it

In the same spirit, you can also use ollas or, on the same principle, bury large unglazed terracotta pots and cover them with a saucer to limit evaporation and prevent small creatures from drowning inside. Once filled, they will slowly release water all around and deep into the soil.

Key takeaway : the simplest method is to use a watering can and irrigate widely around the base, without wetting the foliage. Drip irrigation systems are particularly well-suited for watering tomatoes.

Watering tomatoes: the water bottle trick