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Why do we need to water potted plants?

To understand the importance of irrigation, we must begin with the lifeblood of plants themselves. Cellulose fibers, the polymer from which plants are made, are composed of chains of sugars, specifically glucose molecules, the plant sugar. To create a new leaf or flower, plants need energy, and they generate it like us humans: by burning sugars, specifically glucose molecules.

But where do plants get their glucose? Thanks to the miracle of photosynthesis, they harness solar energy to bind carbon dioxide (CO2) and water (H2O) to produce sugars, releasing oxygen (O) into the air as a byproduct. Plants are therefore a source of oxygen for our homes.

Water is therefore a fundamental element for photosynthesis, the basis of our plants' life. Potted plants, moreover, cannot seek moisture deep within with their roots: it will be up to us to provide the water necessary for their survival.

When should plants be watered?

The correct answer to this question is "when needed." There is no "fixed" rule that applies to all plants and all occasions. The frequency of watering is influenced by many factors, sometimes concurrent. Let's look at the main ones to understand how to build our "model."

First and foremost, the season and temperature play a role. In summer, the sweltering heat will cause the moisture in the soil to evaporate more quickly, requiring more frequent watering. Sun exposure is also important: pots that must withstand the sun's rays during the hottest hours of the day will be thirstier than those grown in the shade.

Equally important is the size of the pot. A small container holds little soil and is completely exposed to the sun's rays: obviously, the moisture will evaporate very quickly. Conversely, a very large pot will be able to retain some moisture more easily.

Finally, let's not forget that every plant has very different needs. Cacti and succulents prefer dry soil and aren't accustomed to too much humidity, which easily leads to root rot. On the other hand, aromatic plants should be watered daily in summer.

The best solution is to dip your finger in the pot and check the humidity level: if it's dry, water; otherwise, wait. Over time, it will be easier to identify the needs of all the plants and water them when necessary.

Watering plants once a week, because we only have time on weekends, is ideal only for some types of plants: succulents are overwatered, and a small pot of basil under the July sun is too underwater. If we don't have time to water the plants, we can use pots with a water reserve: they ensure the right amount of humidity for the roots and alert us when water is running low.

How to water potted plants?

In nurseries and garden centers, houseplants are grown on trays, which are filled and emptied with water to irrigate and fertilize them. This irrigation method is called bottom irrigation: it allows the roots to absorb the necessary water and saturate the soil, without unnecessarily wetting the leaves and above-ground parts of the plants. In wetter seasons, such as spring and autumn, water droplets on the leaves can stimulate the development of fungal spores; it's best not to water the leaves unless necessary.

One way to water potted plants is to fill the saucer with water, waiting 15-20 minutes to allow the soil to absorb the moisture. Finally, empty the saucer and let the excess water drain. Stagnant water in the saucer should be avoided: it encourages asphyxiation and root rot and is a breeding ground for fungal diseases.

Alternatively, if the pots are small, we can move to a sink: water the soil well, even near the edges, and let the pot drain before placing it on the saucer or in the cachepot.

With what water?

Use room-temperature water: if it's too cold, it could cause thermal shock, especially for plants exposed to the sun in summer.

Tap water often contains limescale and chlorine, which are unsuitable for plants. This is especially true for acid-loving plants (such as camellias or azaleas): continued use of limescale-containing water tends to reduce the substrate's pH.

In summer, some plants, such as orchids, require foliar spraying during the hottest days. Even in this case, it's best to avoid limescale water, which leaves whitish stains on the leaves.

We can use rainwater or demineralized water. Alternatively, let tap water settle overnight in a watering can: the limescale will settle to the bottom.

When to water?

In summer, it's best to water after sunset. This will give the roots and soil time to "drink" throughout the night, before the sun's warm rays begin evaporating.

During periods when fungal diseases are most active, such as spring and autumn, it's best to water in the early morning hours to avoid excessive humidity at night.

These rules are especially true for plants grown on terraces. Plants grown indoors year-round generally benefit from fairly stable temperatures and humidity levels.