This factor is crucial for growth. Indeed, all plants contain a large amount of water which can reach 90% of the total weight for herbaceous plants, which consume 300 to 500 grams per transpiration to constitute only one gram of dry matter.

It should be noted that the elimination of water, by transpiration and by evaporation, at the level of the aerial organs, in chlorophyll plants, is variable according to the light intensity, heat and humidity.
The study of the “water” factor therefore leads to examine two main problems that of water in the soil and that of water in the atmosphere, that is to say the problem of relative humidity or degree. hygrometric.

Problems with water in the soil

Below a certain threshold, which varies according to the species, insufficient water in the soil causes wilting of the foliage, then death if the normal water content is not restored as soon as possible.
The insufficiency threshold is reached all the more quickly as the species require a high percentage of underground humidity. This is the case for species of the genera Astilbe, Convallaria, Lythrum Salicaria (loosestrife).
On the contrary, some species cannot permanently withstand wet soil. This is the case for plants of the Cactaceae family and some species of the genus Pelargonium (in particular Pelargonium zonale).
In outdoor cultivation, most ornamental plants die off more from lack of water than from excess moisture, especially when it comes to plants grown in pots and placed in heather soil.

The water existing in the soil is never completely used as food for plants. Indeed, soils do not release part of the water they contain unless they have a certain percentage of humidity, which corresponds to the wilting point of cultivated plants. Thus, for peat, the percentage of preliminary humidity must be of the order of 40% of its weight, whereas it must be only 8% for earth of clay consistency and 3% for fine sand.

The wilting point of plants therefore depends more on the nature of the soil than on the cultivated species.

Steps to be taken to remedy water deficiencies in the soil

Watering is the only way to remedy this. While it is easy enough, by examining the foliage, to tell when a plant needs to be watered, it is quite difficult to determine the amount of water required by the growing soil and to indicate the frequency of watering to be observed, the speed of the soil drying out being variable according to the temperature, the light intensity, the humidity of the ambient air and its eddies.

As the purpose of watering is to restore the removed water to the cultivated soil, its frequency and intensity must be greater the higher the temperature and light intensity, the lower the humidity and the lower the humidity. the atmospheric eddies are greater.

It should be noted that the species with thick and fleshy leaves which contain large reserves of water in their tissues can use this water as and when they need it and require less frequent and less intense watering; these plants are called succulents. Plants with dull or whitish, downy or thorny colored foliage have requirements comparable to those of succulents.

The frequency and abundance of watering must go hand in hand with the vegetative intensity; they must be more numerous and more copious in spring than at the end of summer because, in spring, one attends an increase of the radicular system and the air system, which increases the absorption capacities, this increase being matched increased disposal capacities.

In addition to the signs of foliage wilting, the need for watering is particularly pressing for container-grown plants when, upon watering, the water rapidly passes through the earthy mixture, indicating that the interstitial spaces between the molecules have grown in size as a result of the drought.

Another easy to spot sign of the need for watering is the discoloration of the soil surface (gray or whitish tones).

It is necessary to prevent the cultivation soil from being in a permanent state of humidity, this soil having to present at most a marked state of freshness. It is important that, between two waterings, the earthy mixture can dry up, that is to say, for a short period, regain relative drought.

The best water is rainwater. Tap water can be used, but this has the disadvantage of always being more or less calcareous, which is detrimental to calcifuge species, that is to say fearful of limestone, as well as to those to be cultivated in acidic soil (heather soil). Among these species, mention may be made of those of the Fern family or of the genera Azalea (azalea), Cyclamen, Ficus, Hydrangea (hydrangea).

For these species, if the tap water contains an excessive percentage of limestone, it is possible, in the case of small plants and if the number of plants is not too large, to use mineral water. of the neutral type, qualified as natural.

For potted species requiring an earthy mixture based on heather soil which always takes a longer or shorter time to soak up water, rather than waiting several hours for the soil to be completely watered, watering should be carried out. by immersion, that is to say that we will soak each pot in a container until the water is flush with the upper level of the ground.

For species with delicate foliage and, mainly, for soft plants, avoid wetting the foliage, as water stagnant on the leaves may cause them to rot.

The so-called automatic watering pots and tubs that are found on the market, allow amateurs who fear that they will not be able to water their plants in a regular manner, to remove this worry from them; the same applies to those who are absent during the holidays.

Watering Plant Balcony
© istock

Problems with water in the atmosphere

These problems are linked to the needs of plants to find a certain relative humidity in the ambient air (hygrometric degree). For balcony and patio plants, since they are plants grown outdoors, the problems posed by atmospheric humidity can only be secondary if the soil has a satisfactory water content.

Requirements of balcony plants for the factor

It is only to the extent that the balconies have an exposure depriving them of rainwater that it is advisable to provide the plants with watering as for plants in apartments. However, balcony plants generally have a much lower transpiration, which means that the water withdrawals they take from the soil are also lower and the need for watering decreases as much, except during the summer. .

Since excess water can be drained off without difficulty, the fine apple watering can (greenhouse watering can) can be used without having to worry about the temperature of the houseplants, as with houseplants. water. It is preferable, however, to use water at atmospheric temperature during the summer months.

Requirements of patio plants with regard to the water factor

As terrace plants can benefit from rainwater, their behavior with respect to the water factor is therefore identical to that of outdoor plants.
Additional water should only be provided if the rainfall is insufficient in quantity or periodicity and if the plants and the soil show signs of a need for water such as wilting of the leaves or dryness of the soil.

The conditions to be observed for watering terrace plants grown in containers are the same as for balcony plants.

For plants grown in the ground in the central part of the terrace, it is possible to adjust the watering flow rate in fine rain at will by using a small hydraulic turnstile, which allows for basins when the temperature becomes excessive.

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