How much should I water potted plants

Here's how to water your plants properly

Well-rooted garden plants can usually survive a few days without being watered. If, in the summer months from June to September, high temperatures affect the vegetable and tub plants, but also the perennials in the beds, regular watering of the garden is necessary. This is how you can tell when your plants need water and how to water them correctly.

How to properly water plants

It is best to use rainwater and water penetratingly in the root area of ​​the plants without wetting the leaves. The best time to water is usually in the early morning hours. In the vegetable patch you calculate with around 10 to 15 liters of water per square meter, in the rest of the garden 20 to 30 liters may be necessary on hot days. Avoid waterlogging with plants in pots.

Water plants with rainwater

Rainwater is ideal for watering your plants in the garden. It is not too cold, does not contain any minerals and hardly affects the pH value and nutrient content of the soil. Some plants such as rhododendrons and hydrangeas thrive much better with lime-free rainwater. In addition, rainwater conserves natural resources and is free of charge. The best way to collect rainwater is in a rain barrel or a large underground cistern.

Water plants at the base

While the watering can is usually sufficient for the balcony, a garden hose, sprinkler and watering device are indispensable aids in a garden with beds and lawns if you don't want to get a crooked back from hauling the can. A garden hose with a spray attachment is sufficient for individual plants and small areas. With a watering device, plants can be watered specifically at the base. The water goes straight to the roots and less is lost through evaporation and runoff. In contrast to over-showering the whole plant, this also reduces the risk of infection by fungal diseases. A professional irrigation hose continuously feeds water drop by drop through fine pores to the plants at their base.

How much water do plants need?

Because the upper soil layers dry out more quickly, shallow roots have to be watered more frequently. Medium deep and deep roots get by with less watering. But water so abundantly that the soil is moistened right down to the main root zone. In the vegetable patch you need about 10 to 15 liters per square meter, in the rest of the garden you can expect a watering amount of 20 to 30 liters per square meter on hot days. A weekly water supply of ten liters per square meter is often sufficient for an ingrown lawn. Plants in pots have only limited storage capacities and are not able to tap water reserves from deeper layers of the earth. Therefore, during the hot season, they have to be watered up to twice a day. However, many potted plants die every year in the house as well as on the balcony and terrace due to waterlogging. Therefore, before each watering, check with your finger whether the time is right for the next watering.

A rule of thumb is that one liter of water is needed to moisten a layer of soil one centimeter deep. Depending on the type of soil, around 20 liters of water per square meter are required to moisten a 20 centimeter deep layer. The easiest way to check the amount of precipitation, whether artificial or natural, is to use a rain gauge.

Video: Make your own irrigation systems from PET bottles

In this video we show you how you can easily water plants with PET bottles.
Credit: MSG / Alexandra Tistounet / Alexander Buggisch

When is the right time to pour?

Water early in the morning if possible. It is really important: do not water in strong sunlight! Here the small water droplets on the leaves can act like burning glasses and cause sensitive burns to the plants. In the morning, during the morning warm-up phase from the sun, the water still has enough time to evaporate or pear off without damage.

However, this effect hardly plays a role in lawns - on the one hand the drops are very small because of the narrow leaves, on the other hand the leaves of the grass are more or less vertical, so that the angle of incidence of sunlight on the leaf is very acute. When watering in the evening, the moisture stays longer, but gives predators such as snails the opportunity to be active longer. Infections such as those caused by fungi are also more common because waterlogging promotes their growth.

Tips on how to water your plants properly

  • Condition your plants by not watering as often but lots of water. As a result, plants root much deeper and are still able to reach deeper water even during longer periods of heat. If watered daily but little, a lot of water evaporates and the plants only take root superficially.
  • Water your plants only in the root area and avoid wetting the leaves. This is how you prevent fungal infections in susceptible plants such as vegetables or roses.
  • Especially with very permeable soils, it makes sense to incorporate humus or green manure before planting. As a result, the soil is able to store more water. A layer of mulch after planting ensures that the soil does not dry out too quickly.
  • Many fruit plants such as tomatoes have a significantly higher water requirement during the formation of their buds or fruits. Give them a little more water during this phase - and some fertilizer if necessary.
  • Plants that have been freshly grown and only have short roots require more water than those that are already deeply rooted and those with deep roots. They also need to be poured more frequently.
  • The water in saucers for potted plants should be emptied after heavy downpours. Water that collects there can lead to waterlogging in many plants and thus to root rot. Avoid using coasters in spring and autumn if possible.
  • Terracotta or clay pots have the natural ability to store water and are therefore well suited as plant pots for balconies and patios. At the same time, however, the pots also give off moisture and a little more water is required for watering than with plastic containers.
  • In order to be able to estimate the water requirements of your plants, it is worth taking a look at the foliage. Lots of thin leaves means high water requirements. Plants with thick leaves require less water.

How do plants absorb water?

Plants use various physical effects to get the water they need:

  • Diffusion and osmosis: The term diffusion is derived from the Latin word "diffundere", which means "to spread". Osmosis comes from the Greek and means something like "to penetrate". From a scientific point of view, in osmosis a substance from a mixture of substances penetrates a partially permeable (semipermeable) membrane. The plant roots have a higher salt content than the water in the ground. Due to the physical effect of diffusion, water is sucked in through the partially permeable membrane of the roots until a physical equilibrium is created. However, since the water continues to rise through the plant and evaporates there, this equilibrium is not reached and the plant continues to suck in water. However, if the soil around the plant is too salty, the osmosis is detrimental to the plant. The higher salt content of the soil removes the water from the plant and it dies. This can happen, for example, through too much fertilizer or road salt in the winter months.

During diffusion (left), two substances mix until they are evenly distributed at the end of the process. In osmosis (right), liquids are exchanged through a partially permeable membrane until equilibrium is achieved. Plant roots have a higher salt content and this effect draws less salty water into the plant

  • Capillary effects arise when liquids and tiny tubes or cavities meet. Due to the surface tension of the liquid and the interfacial tension between solid and liquid, water in a tube rises higher than the actual liquid level. This effect allows the plant to move water from the roots up into the plant against gravity. The water transport in the plant is increased by the transpiration.
  • Transpiration: In addition to the effects listed above, there is a heat difference throughout the plant, which is particularly important when exposed to sunlight. The rich green or other, even darker colors of the leaves ensure that sunlight is absorbed. In addition to the important photosynthesis, there is more going on here. The leaf heats up due to the sun's energy and releases evaporating water molecules. Since the plant has a closed system of water channels from the roots to the leaves, this creates a negative pressure. In conjunction with the capillary effect, this draws water from the roots. Plants are able to regulate this effect to a certain extent by opening or closing stomata on the underside of the leaves.