Expert: Long Island Gardener - 10/2/2006

Question
Does the temperature of the water I use to water my daises affect how fast they grow or how well and full they grow?  Can certain temperatures kill plants and can others cause them to grow faster and bloom more often and fuller?

Answer
Amia Marie, I'll try to give you a basic answer on this, but without more information about which daisies you are growing (and there are hundreds from different parts of the world) I can't be very helpful.  I can give you a good general reply, however.  For a better one, let me know what you mean by "daisies".

Temperature plays a very important role in cell growth.  It controls rates of photosynthesis, cell division, and metabolism.  The right temperature is always important.  The air has to be right, the water has to be right, the soil has to be right.  Metabolism is mainly a lot of constant chemical reactions.  For all chemical reactions, there are perfect temperatures where they take place smoothly.  Outside of that perfect range, chemicals reactions slow down.  Or stop.

Now, let's go to one part of the plant that would care about the temperature of your water:  The leaf stomata.

Stomata are the pores of the plant leaf.  You see them mainly on the undersides of the leaves.  

When things are going well, air gets into the leaves through the stomata; Carbon Dioxide (CO2) and Oxygen in the air are absorbed, used for respiration and photosynthesis.

But when the stomata close, respiration and photosynthesis are cut off.  

And that's what happens when you water your plant with water that is too hot or too cold.  Plant hormones in the roots shoot up to the leaves and tell the stomata close up in a desperate attempt to save water.  Some plants are more delicate (i.e., susceptible) than others.  But the bottom line is, if you stress, or shock, your daisies, depending on the plant, you can injure or kill them by shutting down the cell functions.

Exactly what happens to the plant cells?  Mitochondria (which make energy) become distorted; the number of ribosomes (which make RNA) decrease and cell parts change or begin to disappear.  Leaves stop taking in air.  Root cells stop taking in water.  Fatty acids change in the cell membranes, proteins alter, metabolism is upside down.  Free radicals begin to circulate; they damage DNA, proteins and lipids.  Goodbye houseplants.

If you looked at root and leaf cells after watering them with the wrong temperature of water, you would at some point see this happening with a microscope.  Or you could watch a sudden, dramatic drop in root water pressure within minutes of exposure to cold temperatures.

You can see photos of some of the more common damage caused by watering errors on the APSnet feature pages (www.apsnet.org/online/feature/abiotic/water.html).  You can see another view at the University of Florida extension service pages (fawn.ifas.ufl.edu/tools/cold_protection/evaporative_cooling.asp), which I note because as they point out, "It is possible that, on nights when temperatures are close to critical levels, introduction of water could produce more damage than would result if no action was taken."

The West Virginia Extension Service winter "Caring for Houseplants" handout (www.wvu.edu/~exten/infores/pubs/fypubs/WL_167_Houseplants.pdf#search='cold%20hot%20water%20damage%20houseplants'), which you can print out with Adobe, recommends: "Use room temperature water to avoid shocking the plant with cold tap water".

If you need clarification on any of the above, let me know.  If you want more info on your daisies, let me know.  Thanks for writing.