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Why Do We Put Cut Flowers In Water?

Why do we put cut flowers in water? Does it really help?

Cut peonies in a vase.

Dear A Moment Of Science,
What is the point of putting cut flowers in water? Is there any science behind it?
Signed,
Roses Seem Overpriced

Our Answer

Dear Roses Seem Overpriced,
Water keeps cut flowers and other plants crisp because of one of the most important and all-pervasive natural processes operating on the face of planet Earth. It goes by the technical name of osmosis.

Osmosis is the process in which liquid water tends to move toward regions with a higher concentration of dissolved substances. The dissolved substances might be minerals, sugars, anything. Water will tend to move into the region where there’s more dissolved material.

Osmosis And Plants

Here’s how it applies to plants. Each cell of a plant has a membrane; it’s a sort of skin. Water can pass through the membrane easily, but other materials can’t.

Each plant cell maintains a relatively high internal concentration of dissolved materials. Water, therefore, tends to move into the cell, toward those dissolved materials.

As long as the concentration of dissolved substances is higher inside the cell than outside, water will tend to push its way in. Water pressure builds up inside the cell. That water pressure gives a healthy plant its crisp texture.

Crisp

Often that pressure will make cells expand. And from this you can see why plants wilt if they don’t get enough water: the cells lose internal water pressure.

So, plants in general, and cut flowers in particular, stay crisp because dissolved materials, in effect, draw water through the cell membranes into the plant cells by the process of osmosis.

There are other ways living things move water from one place to another, but osmosis is one of the most important.

Sources And Further Reading:

  • Frank B. Salisbury and Cleon W. Ross, Plant Physiology, 3rd ed. (1985).
  • Helena Curtis Biology, 4th ed. (1983).

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