Transpiration in Tomato Plants – water evaporates through a plant’s leaves and is replaced by water absorbed through a plant’s roots – in an unbroken flow.

 

Why this is important for our plants

  • If moisture is unable to evaporate from leaves, a plant cannot absorb moisture and nutrients through its roots.
  • A lack of transpiration (evaporation) is a common cause of Blossom End Rot – interruption to the calcium supply.
  • High humidity in the greenhouse can reduce transpiration and cause BER.
  • Low transpiration can cause nutrient deficiency and reduces growth rate.

 

Pro Tip: Air circulation (aeration) around leaves is important to prevent many problems – open the greenhouse windows when the air inside is humid.

 

It’s like a good sweat! (humans perspire, plants transpire)

Tomato plants lose moisture through their leaves (by evaporation) and absorb water through their roots in an unbroken flow of moisture upwards through a plants plumbing system – a bit like people sweat and replace water by drinking.

 

This helps a tomato plant in several ways …

Nutrients are delivered to a plant in water absorbed by its roots.
If there was no evaporation through the leaves, there would be no water absorbed by the roots. When there is no water flowing through a plant, there are no nutrients available for a plant to feed on.

Plants are cooled by water evaporation in hot weather and receive more nutrients for growth.
The hotter it is, the more moisture is lost through the leaves, so the greater need for frequent watering – especially hanging baskets and small containers.

Some tomato varieties have more leaves than others. The more leaf area, the more water a plant needs and uses.

Also, the more water that flows through a plants system, the greater the amount of nutrients available. Too much nutrient absorption when plants are absorbing a lot of water can cause over-feeding issues.

Pro Tip:  In hot, dry weather when moisture loss (transpiration) is at its greatest, reduce feed if possible.

 

Plant pressure keeps plants with soft tissue upright

When evaporation continues but there is no water for the roots to absorb, pressure (turgidity) drops and plants wilt.
Tomato plants can absorb water through their leaves, just as they can lose it through their leaves, so the quickest way to revive a wilting plant is to mist it with water.

Because the holes in the leaves (called stomata) are mainly on the underside of each leaf, it’s a good idea to mist the underside of the leaves – spraying upwards. This applies to reviving plants and when applying a foliar feed such as a seaweed tonic.

 

More points to consider

  • When it’s cold – Evaporation (transpiration) is reduced so plants receive less food.
  • When it’s humid – Leaves lose less water in humid air than they do in dry air, so plants receive less food.
  • When it’s cold and humid (sounds like every morning in my greenhouse in the early spring!) – plants receive no food!
  • When it’s hot in the greenhouse and the air is damp because there is no airflow, plants get no food – open the greenhouse windows!

Try to keep condensation away with good air circulation in the greenhouse, and try to keep leaves dry if growing outside.

 

 

Save

Save

Save

Save

Save

Save

9 Responses

  1. melisa
    | Reply

    Tomato plants used to be cheap, but now they are not. I am harvesting suckers to grow as plants to save on money.I like to bring plants, or cuttings, indoors just before winter and keep them alive for spring planting. I was not able to do that this past winter, but I plan to do that again this year.It is difficult to keep a very small plant alive, but much easier with a larger plant or cutting.Some cuttings will do fine in plain water without any soil at all.

  2. John
    | Reply

    My wife has been away for a week and asked me to look after the garden. Unfortunately I forgot to water the greenhouse tomato plants. They had no water for 5 days two of which were hot & sunny. They now look badly wilted and the little yellow flowers dried up. I gave them a big water last night. Have I killed them or do you think they will survive?.

    • Nick
      | Reply

      Hi John,
      They may survive – they should revive after being watered within 30 minutes or so.
      Flowers will re-grow on other trusses so there is every hope. Misting them with a foliar spray of water is the quickest way to revive wilting plants.
      Regards,
      Nick

  3. Steve
    | Reply

    This post has nothing to do with transpiration, but I couldn’t see another place to make the posting. I’ve got mate who can’t shut up about an F1 cherry tomato called “Piccolo” Does anyone know anything about it? Should we be growing it? From what I can make out it is an indeterminate variety. Steve

    • Nick
      | Reply

      Hi Steve,
      I haven’t grown this variety myself, but I have heard good comments about it.
      As you say, it’s an indeterminate variety.
      Regards,
      Nick

  4. Dave
    | Reply

    This article provided some very useful information for me. My concern at the moment is wether I will over water or underwater my seedlings, so I’m wondering if I should just mist the leaves rather than watering them from below by pouring water into the trays in which they sit.

    • Dave
      | Reply

      Also I notice that the base leaves have withered on some seedlings that have more foliage than just those two leaves. Is this a bad sign?

      I know those base leaves have a name, but I can’t think what it is.

      • Nick
        | Reply

        These are the seed leaves and they do eventually turn yellow and wither as the energy is sent to the upper leaves and growing tip.

    • Nick
      | Reply

      Hi Dave,
      If the compost is still slightly moist, I would mist them rather than risk the seedlings sat in cold water overnight when temperatures drop.
      Regards,
      Nick

Leave a Reply

Your email address will not be published.