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The Science of Hydration: How Much Water Do Plants Actually Need?

May 28, 2023

Watering Plants – The Ultimate Guide

Water is fundamental to all forms of life, and plants are no exception. It’s essential to the process of photosynthesis, where plants use water, carbon dioxide, and sunlight to produce food and oxygen—a vital component for human survival. But the often-asked question is, how much water do plants actually need? The answer is more complex than you might think, depending on multiple factors like plant type, climate, soil composition, and more. In this blog post, we’ll delve into the nitty-gritty of plant hydration, aiming to equip you with the knowledge to water your green companions optimally.

Why do plants need water?

Let’s start out with a biology refresher, and understand how plants use the water in the soil. Plants need water for several crucial reasons:

  1. Photosynthesis Water is a key ingredient in the photosynthesis process. During photosynthesis, plants use sunlight to convert water and carbon dioxide into oxygen and glucose. This glucose provides energy for growth and development.
  2. Transport of Nutrients Water helps transport nutrients from the soil into the plant. As water is absorbed by the roots, it dissolves minerals and nutrients in the soil, carrying them through the plant’s vascular system to where they are needed.
  3. Cell Turgidity and Growth Water provides turgidity to plant cells, helping them maintain their structure. When plants are well-hydrated, their cells are firm, which keeps the plant upright and strong. This turgidity is essential for growth and for the expansion of new cells.
  4. Temperature Regulation Water helps regulate the temperature of plants through a process known as transpiration. As water evaporates from the surface of leaves, it cools the plant, similar to how sweating cools the human body.
  5. Metabolic and Biochemical Reactions Many metabolic and biochemical reactions in plants require water. These reactions are necessary for various physiological processes, including growth and enzyme activity.
  6. Maintaining Plant Structure In vascular plants, water also maintains the structure of the plant by providing the necessary pressure inside the plant’s stem and leaves. This pressure, known as turgor pressure, is crucial for keeping the plant upright and for the movement of leaves and opening of flowers.

In summary, water is essential to plants for photosynthesis, nutrient transport, maintaining structure and turgidity, regulating temperature, and facilitating numerous metabolic processes. Without adequate water, plants cannot perform these vital functions and may wilt, cease to grow, or even die.

Understanding Plant Water Needs

The water needs of plants can vary significantly based on their species. For instance, succulents and cacti have evolved to survive in arid environments and require far less water than, say, a watermelon plant or a willow tree. On average, most plants lose about 95% of the water absorbed through their roots to evaporation. However, it’s important to note that this percentage can fluctuate significantly depending on environmental factors.

Factors Influencing Water Needs

Plant Species

Plant species play a vital role in determining the water requirement. Different species have adapted to various climates and habitats, which directly affects their water needs. For example, plants native to the desert, such as cacti and succulents, have evolved to retain water in their leaves, stems, and roots. Conversely, plants from rainforest environments typically require more consistent moisture levels.

Soil Composition

The soil is the plant’s reservoir for water. The type of soil also influences how much water a plant needs. Some soils, like sandy ones, drain quickly and hold less water, requiring more frequent watering. On the other hand, clay soils hold onto water longer, but they can become easily waterlogged, depriving the plant roots of oxygen. Loamy soils, a balanced mix of sand, silt, and clay, are generally ideal for most plants as they retain moisture while also providing good drainage.


Weather patterns and climate conditions can significantly affect a plant’s hydration needs. During hot, dry periods, plants may require more frequent watering. In contrast, during cooler or more humid times, plants may need less.

Pot Size and Material

For indoor plants and those grown in containers, the size and material of the pot play crucial roles. Smaller pots dry out quicker than larger ones. Similarly, pots made from porous materials like terracotta lose water faster than plastic or glazed ceramic pots.

Guidelines & Tips for Watering Plants

While it’s challenging to define a ‘one-size-fits-all’ approach to watering plants due to the factors mentioned above, certain principles typically apply:

Deep, Infrequent Watering

Deep watering, where the water is delivered slowly and deeply into the soil, encourages roots to grow deeper. This strategy makes plants more resilient in dry conditions and is especially effective for mature plants.

Morning Watering

Watering in the early morning reduces evaporation, giving the plants ample time to absorb the water before the heat of the day. It also helps prevent the growth of fungal diseases that can develop in the cooler evening temperatures with damp leaves.

Checking Soil Moisture

Rather than watering on a set schedule, check the soil’s moisture levels. You can do this by simply sticking your finger into the soil. For most plants, the top 1-2 inches of soil should be allowed to dry out between watering. More on moisture meters here: How to use a moisture meter in soil.

The Role of Technology

With advancements in technology, tools like soil moisture sensors, automated irrigation systems, and smart plant monitors can help gauge a plant’s water needs more precisely. These tools can be particularly useful for larger gardens or for those who want to optimize their watering schedule. Not only can this technology save water and promote healthier plant growth, but it can also make gardening more manageable and enjoyable for those with busy lifestyles.

Watering Indoor Plants

When it comes to watering indoor plants, similar rules apply. Still, indoor environments present unique challenges such as lower light levels, less air circulation, and consistent temperatures, which can influence watering frequency. Overwatering is a common problem with indoor plants. Many houseplants prefer their soil to dry out completely between waterings.

Interestingly, signs of overwatering can often mimic those of underwatering, such as yellowing leaves and wilting. This is because both underwatering and overwatering can lead to a lack of oxygen reaching the plant roots, causing them to suffocate and eventually die. Regularly checking the soil moisture and understanding the specific water requirements of your indoor plants can help avoid these issues. You can find a list of great watering cans for indoor plants here: Best Watering Cans for Indoors

How much water is enough?

A good rule of thumb for watering plants is the “1-inch per week” rule. This guideline suggests that plants typically need about 1 inch (2.5 cm) of water per week, either from rainfall or manual watering.

What About Rain?

Rainwater can provide significant benefits for plants. It’s generally softer than tap water and contains useful amounts of nitrogen and other nutrients. However, it’s essential to ensure that plants aren’t becoming waterlogged during particularly wet periods, as this can lead to root rot and other problems.

For those living in regions with regular rainfall, it might be worth considering setting up a rainwater harvesting system. This way, you can collect and store rainwater for use in your garden during drier periods.

Water Conservation Considerations

With water scarcity being a concern in many parts of the world, it’s important to consider water conservation in your gardening practices. Using techniques such as mulching, efficient watering systems, and choosing drought-tolerant plant species can significantly reduce water use. Not only will these strategies save water, but they can also save you time and effort in maintaining your garden.

In conclusion, understanding how much water plants need is a combination of science and careful observation. Each plant species has its unique water requirements, and these can change depending on environmental factors. The more in tune you are with your plants and their needs, the better you’ll become at providing them with the optimal amount of hydration. Remember, overwatering is just as harmful as underwatering. So, pay attention to your plant’s signals and adjust your watering routine accordingly.


  1. University of Arizona, Cooperative Extension. Plant Water Requirement
  2. USGS. The Water Cycle: Transpiration
  3. NC State Extension. Plant Water Needs
  4. University of California, Division of Agriculture and Natural Resources. Soil Type and Watering
  5. The Old Farmer’s Almanac. When to Water Plants
  6. University of Illinois Extension. Container Gardening
  7. Colorado State University Extension. Watering a Home Landscape During Drought
  8. The Spruce. [Best Time to Water Plants](