Evaporation

You already know what evaporation is, right? I’ll bet there’s more to it than we know, so let’s find out!

Hillside mist (StockSnap) Pixabay

Okay, so what is evaporation?

Technically, evaporation is the process of turning a liquid into a vapor without forming bubbles. As soon as bubbles happen, we call it boiling. There shouldn’t be any boiling in the garden, but  you can bet there’s a lot of evaporation going on! But how does the liquid actually turn into a gas? It ends up, at the molecular level, as something is heated, all those molecules move around more. Then they start banging into each other. Eventually, they start to fall apart, transforming into a gas. That’s evaporation.

Plants and evaporation

If you’ve been reading The Daily Garden for a while, you may recall a post called evapotranspiration. If not, give it a read. It’s really short. Okay, so plants absorb water through their roots and move it around in the xylem, and then lose water through tiny holes on the underside of leaves, called stoma. This process is called transpiration. You may be surprised to learn that plants only hang on to 2 or 3% of the absorbed water. The rest is lost to evaporation through transpiration and guttation. [Think of guttation as sweating.]

Wilting summer squash

Evaporation and irrigation

The bulk of water loss through evaporation happens to the soil around your plants, leaving them high and dry. Farmers use complex equations involving rates of evapotranspiration to decide how much water to give their crops. We don’t have that much technology in our gardens or landscapes, but we can use what we know about evaporation to reduce water loss and water waste. Here’s how:

• use drip irrigation and soaker hoses
• water at night or in the early morning
• avoid watering during the heat of the day
• water deeply and infrequently, to encourage deeper root systems

Just because a plant wilts during the hottest part of the day does not mean you need to run outside and turn on the hose. Wait to see how the plant is able to recover in the evening. If it stays wilted, then water it. If it perks back up, then it has not lost too much water through evaporation.