Plants and water

In herbaceous plants water maintains the turgidity of the plant and without it we see the plant wilt. All plants require water for photosynthesis and other chemical reactions.

Most plants have adaptations that help them conserve water, particularly plants from arid environments. Water and plants is a very big topic, I once attended a 5 day plant physiology conference (East Berlin, August 1989) solely on the subject of  water and plants responses to it.

 

Adoptions that prevent water loss

The ones you’ll see most often, particularly in vegetables, are…

• Hairs on leaves (beans, tomatoes, apples)
• Waxy leaves (cabbages; beans; fruit trees)
• Dissected leaves which reduce the surface area (carrots, fennel, asparagus)
• Blue-grey colouration (also waxy) reflects light and heat (cabbage, broad beans, asparagus)
• Small rolled leaves (rosemary, lavender)
• No leaves (broom... not a vegetable I know! However, some varieties of pea have enlarged stipules but no leaves)
• Thick leaves and stems (succulents)
• Other less obvious adaptations are large root system, long tap roots (carrots, parsnips, tomatoes), stomata on the underside of leaves and a reduced number of stomata and sunken stomata

There are also many physiological adaptations that prevent water loss. Some plants have a high level of control over their stomata and will close them in the middle of the day when temperature reaches a certain threshold, soil water is reduced or another factor becomes limited.

Most succulents have the ability to photosynthesize at night by storing energy from the sun. Grasses including Corn have a different biochemical mechanism to fix carbon that uses water more efficiently in drought conditions.

Watering

Some of these strategies while they may be beneficial to the plant and prevent them dying during a drought may not be that useful to the vegetable grower whose main ambition is a large harvest. Watering is important in the sort of weather we have been experiencing over the last few months. However having left my neighbour to water my home garden while I was on holiday and come home to find some over watered and dying and others under watered and dead I realise not everybody quite understands how to water.

In most cases it is better to give plants a lot of water and leave them for a few days rather than just give them a dribble of water every day.  Doing this makes the plant grow it’s roots deeper into the soil, watering a little everyday means it doesn’t need to and if you don’t water one day the plants may wilt and die quite quickly.

Jude