Water and irrigation in plants

Today in Gardenprue, we have to talk about an essential element for the growth of plants, water. We will tell you some problems that appear in irrigation and their solutions, as well as some irrigation techniques to avoid fungal growth problems and disorders due to excess or lack of water. You will find the explanation to many doubts you had about irrigation. Enjoy it!



Plants have a high amount of water in their composition (80-90%), except for dry parts, wood or seeds (from 50% to 18%).

This water is divided into two parts: the first is the component of the structural material, the cells and that of essential materials, it is the water that is related to the turgor of the plant.

The second is part of the sap, it is the circulating water since it dissolves the nutrients thanks to its chemical properties.

The water absorbed by the roots is lost by evaporation   through the leaves, perspiration, in very high proportions, 9 out of 10 parts are used to cool the leaves, the same proportion as an iceberg (note: I don’t know if it comes the case but it is an easy example to remember), that is why if a plant is not fresh it does not perform the transpiration function correctly it is important to find out the cause.

Some mornings, certain types of plants have a few drops on their leaves. It is not dew , it is the water pressure in the roots that is much higher than in the leaves.

This does not happen neither in large bushes nor in trees.

The plant has a greater capacity to evaporate more water in summer than in winter, since temperature and other physical-chemical factors influence circulation. The cold winter wind dries the leaves as if it were a hot summer wind, we say “burns” them.

Plants cannot evaporate enough water.

This beautiful flower emerges between the thorns, leaves, of the specimen. The chlorophyll function is carried out by the stem which is in turn covered with a thin waxy layer, hence those whitish tones that these cacti usually have.

Plants to defend themselves against such a problem, excess evaporation , have evolved over time, replacing leaves with thorns, cacti, or thinning their leaves, coniferous needles, or covering themselves with various types of hairs ( Tradescantia Sillamontana) , or waxes.

In this way they evaporate less water. Others are simply deciduous, remove the sap, which is very expensive, and drop the leaves in yellow and orange tones, xanthophyll, and its similar canthaxanthin that turns crustaceans red when cooked.

We have just discovered something: as a general rule, acicular, prickly, hairy or waxed plants will need less water than their counterparts under the same conditions.

And I’m going to the opposite side. Many plants, especially tropical, which we know as “indoor” suffer from “lack of water because they have the tips of their leaves brown” and therefore we water them more.

Big mistake : almost all of the times the plant has lacked water due to being flooded, most likely due to having it in a pot (we will talk about them) or watering it with a dish underneath.

We return to the principle: ” For a root of a plant to take in the surrounding water from the ground, there must be oxygen around it “, if I go under water I lack air, because they are exactly the same. And the swamp cypress? Well, it has pneumatophores  through which it takes the necessary air.

Only aquatic plants and algae absorb CO2 through the roots, which is why the proliferation and invasion of aquatic plants in a pond, some can double the mass in 24 hours, duckweed – Lemna minor – or spectacular growth of some algae such as Sargassum in whose shelter eels grow.

When we have a plant in an enclosure without aeration, pot or similar, although the pot has drained the water vapor from the humid substrate and the reactions that take place, both chemical and bacterial, emit gases that displace the air with its oxygen, little by little. little roots lose their function, the plant at first seems to lack of water, but it is the opposite .

In wicker, bamboo or similar pots this does not happen, the air circulates calmly.

Without being true or false, I believe that during the night the plant releases CO2 which, being heavier than air, gets into the pots, displaces oxygen and the plant suffers from the problem of not having enough to obtain water even though it is around of mycorrhizae.

They, in turn, undergo a fermentation process that makes them useless for plants, it is noticeable by the brown or brownish color of the roots. If someone has a fine nose, they will smell something acidic like vinegar, a memory like opening bags of slightly stale bean sprouts.


SOLUTION: eliminate flower pots. Put stones or pieces of tile under the pots and on the plate so that the water that runs off does not touch the bottom and the roots are always aerated. The drained water in the dish evaporates and helps the plant moisture without the need for diffusion wetting.


It is also true that some plants need extra humidity and it can be good to spray them, not too much. But with what kind of water? When hard water evaporates, it leaves a white lime residue on the leaves, most of the water comes from the tap and contains dissolved chlorine.

The solution is to use the water from the heat pump (air conditioning / heating).

Yes, even for irrigation, but we must meet a series of conditions. As we know, the water from the heat pumps does not have dissolved mineral salts and it will steal those from the earth, impoverishing it .

If we add a few drops of a liquid fertilizer the problem is solved, but if we are in a calcareous area it is not enough to give it an irrigation with the fertilized water, at very low doses, and that eliminates salts, those so ugly that they accumulate in the earth in the form of somewhat whitish granules.

It is a matter of practice. If it is for spraying, mix it with 20% tap water or a few drops of foliar fertilizer.

If you do not have this type of water, ask the bar below, you will not have to throw it away. You will not keep it for long either, it is water without chlorine. Keep it covered so that no pet or bird drinks from it.

In summary: the roots take water, thanks to ATP, and there must be oxygen available, oxidation, which increases the water pressure in the lower zone, passes to the primary xylem and this forces the water to rise through the intercellular spaces preferably, apoplast , and / or by the syplast, a more difficult path, from here to the atmosphere through the stomata, for simplicity.


As the plant evaporates, it loses turgor, recoverable vacuolar water, and then non-recoverable or hardly recoverable cellular water, the leaf dries and dies , or the whole plant. This water is what we must supply to the plant without excess. Let’s see which methods are the most convenient to water our garden, terrace or indoor plants.

The best irrigation is the hose in small gardens


Because one knows where more water is needed, because one sees the hibiscus aphids while contemplating the flower or the mealybug of a laurel. If the garden is very big my idea is not good. Let’s apply a drip system in bushy areas and sprinkle in lawns.

If you water with a hose, you can clean the plant of aphids by spraying a little hard, not with a clean stream. When you water again you will have aphids, they are very prolific, spray them again.

The jet of strong water can be applied to laurel or  ficus nitida when the cochineal invades them.

In the case of outdoor pots, the water can be supplied with the various artichokes that exist on the market, better those with a small 50 to 70 cm lance, and with an opening / closing valve, it will help us not to bend over and that the water does not fall violently against the earth and stain the soil digging up the roots of the plant.

To prevent the water from wetting the soil, we put a plate under the pot, and as a recommendation to prevent the water from touching the pot, pieces of brick are placed between the two (like the previous image)

The amount of water is important : if we water little, all the salts dissolved in the irrigation water precipitate on the ground, so we must irrigate by letting some water out, that water will have dragged the salts from the previous irrigation, but if we water very abundantly With the same wash, we will take the salts that are easier to dissolve, which are precisely the ones that the plant needs the most.

Once verified that it is not any type of spider, this Calathea has arranged not to lose more water by evaporation by rolling up its leaves. The necrotic parts are dead, the loss of water is irreversible. The rest of the plant is fine. This plant will replace these leaves this spring.


There are discussions about it. One theory says that the substrate must always be kept moist, it is the most common practice in production greenhouses, and it is the way that the plant does not suffer from water stress and dedicates all its energy to growth and flowering, which is what sells.

I have practiced this system in many of the greenhouses that I have advised, but we water little many times, and the plants are treated.

Now, however, I am going the other way for a very different reason.

If in the previous case we have a controlled irrigation, desalinated water with injection of fertilizer, heating and humidity according to programming, at home the temperature fluctuates, the luminosity is what we have, air currents abound, the water is not the most appropriate If we cause excess water to all of this, the plant will become ugly.

It is preferable to wait until the earth is somewhat dry to water. If we go over, we empty the water dish. But if we do not arrive, that we water little or we return from a trip and that the root ball of the pot is contracted, do not get nervous, we take the pot and water it in a sink.

A little water, let it drain, another little water, let it drain, and so on until we see the substrate wet enough and we take our plant to its place.


That the tips of the leaves turn brown and then black. If we continue to maintain humidity, the entire leaf turns black until the plant dies.

This is due to the fungi of the earth and there is a family of them, in particular, that is anaerobic (lives in the absence of oxygen) and at depths of 30 cm or more. When the earth is flooded the fungus rises entering through the roots and ( phyton = plant; phthotra = destruction) the plant goes to hell.

Anthurium andreanum attacked by phytohpthora. The new leaves come out very healthy but the crisis will return the moment we go over with watering or keep water at the bottom.

In the above case, the dry parts do not have to be cut. It is a scar area and it will spread, there may be fungi and we will transmit the disease again.

But when the earth dries , this fungus of evolution different from the rest because they have their cellulose cell wall, it becomes aerobic (presence of oxygen). It is a fungus called facultative, which gives it the ability to attack again when excess water exists.

From here you can see why I prefer to water from the top, little and slowly, let it drain and water (wetting the leaves or not is to the taste of the watering and the humidity of the environment and the type of plant) than to water it by leaving it in a container and to absorb, as the fungus rises.

And the disinfection of free chlorine in the water is not worth me, since it would attack the roots first than the much more resistant spores.

The problem that arises is that the substrate will retain a lot of moisture and the water will form a continuity through which the aforementioned fungus, and many others, will rise, facilitating its subsequent attack. In greenhouses it is prevented with its doses of fungicides, but it does nothing to the fungal spores.

These spores will wait for the most convenient moment to wake up and attack, the curious thing is that they always do it at home.

When it comes to spray irrigation, you have to be an artist. Although it is good for the leaves, the problem is that the lower part of the roots remains dry and therefore they cannot perform all the functions that have been entrusted to them.

Therefore and with the aforementioned: water for spraying or spraying plants should be slightly calcareous , not tap or shake before use, and water the soil enough to keep it moist . It is convenient, from time to time, to water these pots abundantly to carry out a wash.

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