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Water travels up through a plant, against gravity, from its roots to its leaves, through a network of xylem vessels

Xylem vessels are the pipework in plant stems that transport water and minerals from the roots to the rest of the plant. . The pulling force that generates this movement is created by water evaporating from the leaves, in a process called transpiration

Transpiration is the process by which water is lost from pores in the leaves. This creates a pulling force that moves water up through a plant from roots to shoots, vital for their survival and growth. :

Water moves into and through a plant by osmosis, from a place where it’s abundant to a place where it’s less so. In the leaves, water moves from xylem vessels in the veins, into leaf cells, and out into the spaces between cells.

As water moves out of leaf cells it is warmed by the sun and evaporates, filling the spaces with water vapour. Once these contain a higher concentration of water than the outside air, the vapour diffuses (moves) out.

Water lost from the leaves is replaced by more from leaf cells, and in turn from xylem vessels in the leaf, stem and roots, and finally from soil water, creating a continuous pull.

Water is cohesive (its molecules are attracted to each other and cling together) and adhesive (it 'sticks' to cell and vessel walls), so it moves as a column up through a plant.

When you dig up a plant, removing its roots from the soil, you break the continuous stream of water moving through it. You may see temporary wilting and a check in growth as a result. Giving plants a good drink before and after moving them helps to reduce this interruption.

For more advice see our guide to moving trees and shrubs .

The pull of water through a plant, created by transpiration

Transpiration is the process by which water is lost from pores in the leaves. This creates a pulling force that moves water up through a plant from roots to shoots, vital for their survival and growth. , has a number of important functions:

• it delivers soluble mineral nutrients
  To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key nutrients usually taken up from the soil are nitrogen, phosphorus and potassium. Plants also need carbon, oxygen and hydrogen to make carbohydrates — their main energy source. Carbon and oxygen come from the air as carbon dioxide, while hydrogen is drawn from water absorbed by the roots. Other important soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough of these nutrients to support healthy plant growth. to the places where they’re needed for growth
• it delivers water, a raw material in the process of photosynthesis
  Photosynthesis is the process by which plants make their own food, harnessing the energy in sunlight to fuse water (absorbed from the soil) and carbon dioxide (absorbed from the air) to create simple sugars. , to the leaves
• it keeps cells plump and firm, providing stability and helping plants stay upright
• it keeps plants cool, as water evaporating from warmed leaf surfaces takes heat away with it

A mature tree can drink up to 900 litres (200 gallons) of water a day, yet plants lose most of the water they take up. Only around two per cent is used in processes like photosynthesis

Photosynthesis is the process by which plants make their own food, harnessing the energy in sunlight to fuse water (absorbed from the soil) and carbon dioxide (absorbed from the air) to create simple sugars. and tissue building. Uncontrolled, this loss of water would be fatal for a plant.

Luckily, plants have a way to conserve water when they need to – the leaf pores through which water vapour escapes, called stomata

Small pores on the surface of leaves that allow for gas exchange, including the intake of carbon dioxide for photosynthesis and the release of oxygen and water vapour. , are bordered by guard cells that act as doors to open and close each pore (stoma). When roots detect dryness in the soil or when water is lost from leaves more quickly than it can be replaced, a chemical signal is sent to these guard cells to close the pores.

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Plants originally from regions of low rainfall often have other leaf adaptations to reduce water loss:

• thick waxy cuticles
  A waxy, protective layer on the surface of leaves and stems that helps to prevent water loss. It also provides a barrier against insect feeding damage and diseases. The thickness and composition of the cuticle can vary depending on the plant species and environmental conditions. (the coating on leaves) create a barrier to evaporation
• narrow leaves with fewer pores reduce the amount of water escaping
• leaf hairs insulate, trapping air and moisture, to reduce the rate of transpiration
  Transpiration is the process by which water is lost from pores in the leaves. This creates a pulling force that moves water up through a plant from roots to shoots, vital for their survival and growth.
• sunken stomata slow air currents and reduce vapour loss

As these plants are adapted to lose less water, they need to drink less as a result, so take care not to overwater if you have them growing in your garden.

For more plants suited to dry conditions, see our guide to drought-resistant plants .

Stomata

Small pores on the surface of leaves that allow for gas exchange, including the intake of carbon dioxide for photosynthesis and the release of oxygen and water vapour. close in the dark, stopping water vapour from escaping and reducing the effect of transpirational pull. Even so, root pressure still pumps some water up through a plant at night. To preserve their water and nutrient balance and prevent cells rupturing under pressure, some plants lose excess water by guttation

A process by which some plants lose excess water by exuding sap droplets overnight through specialized pores called hydathodes, usually found at leaf margins. This process helps plants relieve water pressure in their cells and avoid damage. It is often seen as a result of overwatering, and can be mistaken for early morning dew drops. . They exude sap

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding. droplets overnight through specialised pores, called hydathodes, usually found at leaf margins. These droplets can be mistaken for dewdrops in early morning.

If a plant takes in more water than it can let out, its cell walls eventually burst under pressure, causing water-soaked patches on the leaves that turn corky. This is known as oedema , and can usually be remedied by reducing watering.

In humid conditions, transpiration

Transpiration is the process by which water is lost from pores in the leaves. This creates a pulling force that moves water up through a plant from roots to shoots, vital for their survival and growth. slows down, as the concentration of water inside a leaf is no longer much higher than the outside air. As less water is lost from a leaf in these conditions, less is needed by the roots to replace it.

Conversely, in warm and/or windy weather, transpiration speeds up as water evaporates faster at higher temperatures and moving air currents wick moisture away from around a leaf. In these conditions, plants need plenty of water to replace what is lost and are prone to wilting if this isn’t available.  

You can change the humidity

The concentration of water vapour in the atmosphere. This affects the rate at which plants transpire (lose water from their leaf pores), which in turn affects how much water their roots absorb from the soil. If air humidity is low, plants transpire quickly and become at risk of wilting if water is lost from the leaves faster than it can be absorbed by the roots. Different plants require different levels of humidity to thrive. Many tropical houseplants need high humidity and are best grown in a steamy bathroom, misted regularly or placed on a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor or overhead misting. level around your plants to suit their needs, helping them to stay happy and healthy:

In our homes

The air in our homes tends to be quite dry, especially over winter when the central heating is on. Houseplants are at risk of losing more water than they can take up, resulting in dry, crispy leaves, leaf drop and wilting. So, if you grow houseplants:

• Mist plants regularly, especially those from humid, sub-tropical climes
• Group plants together to raise air humidity around their leaves
• Stand plants in saucers of wet gravel
• Grow plants in a terrarium

In the greenhouse

Greenhouses heat up quickly on sunny days, increasing the rate plants transpire and the amount of water they need to drink. To look after your greenhouse plants:

• Damp down
  In a greenhouse, damping down means wetting floors and other surfaces to lower the temperature and add humidity. This helps to prevent plants from suffering heat stress. the floor on hot days to increase relative humidity
• Use greenhouse ventilation and shading to reduce the temperature
• Mist foliage regularly
• Pay close attention to watering – especially seedlings
  A seedling is a young plant grown from seed. and young plants growing in small volumes of compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

In the garden

It’s harder to control humidity levels outdoors, but there are still a few things you can do:

• P lant a windbreak if your garden is exposed, to slow air movement and raise the humidity around your plants
• Group together container plants, especially those on sunny patios
• Improve your soil by digging-in organic matter , so it holds more water for roots to drink
• Pay close attention to watering in warm and/or windy weather – especially new plants and those in containers.

Now you know more about how plants lose water, put this into practice to help your plants thrive:

• Give plants a good drink before and after moving them to reduce interruption to the transpiration
  Transpiration is the process by which water is lost from pores in the leaves. This creates a pulling force that moves water up through a plant from roots to shoots, vital for their survival and growth. stream
• Plant a tree to cool your garden's microclimate – see our guide to trees for smaller gardens
• Choose plants with narrow, hairy or waxy leaves if you have a hot, sunny garden or free-draining soil, as they are adapted to lose less water – see our guide to drought-tolerant plants
• Check your plants regularly in warm and/or windy weather, when transpiration speeds up, to ensure they have enough water at the roots
• Raise the air humidity
  The concentration of water vapour in the atmosphere. This affects the rate at which plants transpire (lose water from their leaf pores), which in turn affects how much water their roots absorb from the soil. If air humidity is low, plants transpire quickly and become at risk of wilting if water is lost from the leaves faster than it can be absorbed by the roots. Different plants require different levels of humidity to thrive. Many tropical houseplants need high humidity and are best grown in a steamy bathroom, misted regularly or placed on a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor or overhead misting. around your houseplants, especially when the heating is on, to avoid the damaging effects of drying out