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How to water plants. Answers to when and how to water plants in your garden

Watering plants

What is the best time to water the plants?

The question about the best time to water plants has actually two answers. We can water plants in the early morning or late afternoon.

Watering plants in the early morning

The best time to water plants is early in the morning while temperatures are still low. Early morning watering will give the water time to reach deep into the soil and be gradually absorbed by the plant roots, without losing valuable water to evaporation.

Watering plants early in the morning will make water available to the plants for the rest of the day, so they can effectively deal with the sun and heat of the rest of the day.

As always, what’s good to keep in mind is not to get the leaves wet. If the sun is strong and the drops that have fallen on the leaves don’t have time to evaporate, they can act as lenses and cause sunburns on the leaves.

Watering the plants in the afternoon

If you can’t water plants in the morning, the second best time is in the afternoon, after 5:00 pm.

If you water your vegetables in the afternoon, the extreme heat will be gone, but there will still be enough to evaporate any drops that fall on the leaves.

Watering in the afternoon or early evening also limits evaporation and gives the plants several hours to absorb the water.

When watering in the afternoon, you should be doubly careful not to get water on the leaves of the plants. Moisture on the leaves in the evening hours increases the chances of fungal infestations.

Watering the plants in the night

You should avoid watering plants at night. There is a risk of mold growth and fungal attack.

Only water at night in an emergency, so that the plant can be watered immediately.

Water less than you would at other times.

Watering plants at midday

Avoid watering plants at midday and during hot and sunny periods.

Water at midday only if absolutely necessary. Do not wet the leaves because there is a serious risk of burning the leaves from sunburn.

How much water the plants need. How much to water them?

How much water does a plant need? How much should we water it?

The easy and simplest answer is enough to keep it healthy and healthy looking. Be vigorous without symptoms of water shortage. Empirically in our garden, we can see when our plants need water and water them.

Each plant has its own water requirements. These depend on a number of parameters such as:

  • The type of plant
  • The depth of its root system
  • The type of soil
  • Environmental conditions

What is worth knowing is that 70% of the water is absorbed by the roots located at 50% of the depth of the root system.

In other words, if a plant’s root system reaches a depth of 30 cm, 70% of the water we water it with, is absorbed by the roots located at the first 15 cm. So we have to drop enough water to reach this depth.

Το 70% της ποσότητας του νερού, απορροφάται από τις ρίζες που βρίσκονται στο 50% του βάθους του ριζικού συστήματος του φυτού
70% of the water is absorbed by the roots at 50% of the depth of the plant’s root system
Source: Irrigation – Drainage of green projects. Section 9: Calculating the water requirements of plants. Dr. Tsirogiannis L. Ioannis

Soil and watering

An important factor in determining how deep the water can reach is the quality and composition of the soil. It is easy to understand that in a sandy soil, water will penetrate more easily to a greater depth than in a dense, rough soil. In dense, unworked soil, water will drain before it can be absorbed by the soil. It will be a waste of the watering if we don’t first till and if we don’t pour the water a little at a time, rather than all at once.

If the plant can’t develop the root system deeply, it will try to do so broadly. But that doesn’t mean the quality will be the same. Horizontal root system growth is a solution of necessity for the plant. A panic solution. An attempt to survive by seeking water. Not something normal.

Calculation. How much water does a plant need

Knowing all of the above, the question remains. How much water do we need to give to a plant to water it properly?

To be able to answer this question  we need to know two more parameters. The surface we are watering and the depth of the root system of the plant we are interested in. To make life easier for us, let us consider that in most plants (vegetables) the roots reach a depth of about 0.30 meters (30 cm).

With this information, we can calculate the litres of water a plant needs using the following simplified formula:

Watering Water Volume (in litres): ( π * R^2* (0.5 * D) ) / 1000
π = 3.14
R: the irrigation radius around the trunk of the plant (in meters)
D: the depth of the root (in meters)

Assuming that we water within a radius of 0.10 meters and the root depth is 0.30 meters, by substituting we have the following:

( π * 0.1^2 * (0.5 * 0.3) ) / 1000 = 4.7 liters of water

So we need to water this plant with almost 5 liters of water.

If we change the watering radius to 15 cm, then we will need almost 10.5 litres of water.

How often should we water our plants

Here the answer is not one for all and I will not venture to say you should water every day, or every other day or whatever.

The answer to the question how often should we water our plants, is influenced by many parameters. I will mention a few:

  • The type of plant
  • The type of soil
  • The environmental conditions
  • The temperature of the environment
  • The evapotranspiration
  • The growth phase of the plant
  • Whether it has rained or not

Empirically, we can say to water when the plant seems to need water or when the soil at some depth is dry.

For those who want to delve deeper into the subject of calculating the water needs of plants, I refer you to the excellent work of Dr. Ioannis Tsirogiannis at Technological Institute of Epirus, Greece.

You can study two of his many excellent notes:
Calculation of plant water requirements

How to water potted plants

Water potted plants slowly so that the soil has time to absorb the water. We don’t want to pour water fast, so that it runs off the pot, but in fact the pot is left dry.

You will often run into an advice about when to water potted plants. Use your finger. Put your finger in the soil to test the humidity. If the soil feels dry, it is time to water the plant.

Bonus Info

In 2007, I had helped (on a programming level) Dr. Yannis Tsirogiannis to implement an online crop irrigation management system in the Arta, Greece region. To my surprise, I noticed that the online system is still (2018) being used to provide irrigation advice to farmers in the Arta region.

The system automatically receives meteorological data. By implementing mathematical formulas (given to me at the time by Mr. Tsirogiannis and mentioned in his notes that I am giving you), the type of crop and the environmental conditions, it manages to calculate when and how much watering the crops need in order to have the optimal yield without wasting precious water.

You can find it here: ProBioSis Water Management – Crop irrigation management in the Arta, Greece region




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