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Watering Greenhouse Tomatoes

How much and how often to water tomato plants, and other plants, is not an exact science. There are too many variables to lay down hard and fast rules. The size of the plants, their vigour, the type of compost / soil, temperatures and amount of light will all affect watering requirements.
But there are some basic rules which can be followed by amateur greenhouse gardeners which should ensure a reasonably accurate supply of water and nutrients. We explain these below and highlight the important different parts of of a tomatoes root systems. The need for potash and nitrogen are also considered.



One of the most frequently asked questions about greenhouse tomatoes is how often and how much to water. The only true answer is that it all depends on the too many variables to give a hard and fast single answer. But our estimate for average conditions is that each greenhouse plant will require 1.1 litre / 2 pints of water per plant per day. The key variables which will affect that estimate are:

Temperature / sun - in cool cloudy conditions, water requirements will be about half the above estimate; in warm full sun conditions water requirements will be about 50% more.

Growing method - if grown directly in the soil, then watering requirements will be less, depending on the soil type. If growing in bottomless pots with a gravel type base then watering requirements will be slightly more.

Aside from the very imprecise estimates given above two other methods can and should be used. First is visual examination of the soil. It should be moist but not water-logged. Examine not only the surface of the soil but also the dampness of the soil 5cm / 2in below. When growing tomatoes in bottomless pots especially, the top surface of the soil can look dry but just 3cm / 1in below the surface, the compost can very moist.

The second indicator of water needs is the appearance of the plant. If it is wilting then, disease aside, it probably needs watering. For more long term watering requirement, it is common for over-watered tomato plants to have lighter green foliage compared to normal. The lower leaves will start to yellow. Reduce watering if this is the case.

Under-watered tomato plants tend to have darker than normal foliage which is harder and in severe cases it begins to go crisp. Increase watering in these cases.

Watering frequency - little but often is the best rule. This will ensure an even supply of water which is good for tomato plants. Infrequent applications of large amounts of water will cause the skin of the fruits to split.

MULCHING - when growing tomatoes directly in the soil or in bottomless pots, a layer of mulch on the surface will help retain water and reduce the need for watering. Black plastic sheet can be used or a 3 to 5cm / 1 to 2 in layer of chipped bark for a more attractive finish. Gravel is another alternative for pots.

AUTOMATIC WATERING SYSTEMS - there is a wide range of watering systems from the various horticultural companies online and in garden centres and diy stores.


Automatic watering system for a greenhouse When you have mastered your chosen system they are an excellent method of automatic watering. They also provide an excellent backup if you plan to go on holidays during the growing season.

On the left (click to enlarge the picture) is a basic system. It consists of an tap attachment which supplies water at timed intervals. The water is piped to the greenhouse and small nozzles spray water over the soil.


The nozzles can be set high or low as required. For reliable and value for money greenhouse watering systems click here to go to our recommended supplier.