The water cycle is a global phenomenon, but something similar is happening in your garden.
In its simplest terms, the water cycle describes how water moves around on the Earth’s surface. It might be moving very slowly as ice in a glacier, whipping around on the wind as a gas, or flowing across the soil surface to water your bean plants. Regardless of its form, the mass of water on Earth stays relatively unchanged. The same is not true of your garden.
Unless you water exclusively from a rain barrel, the water for your garden probably comes from a spigot. If you’ve ever experienced a water main break or a flood, you know just how devastating too much water can be.
Let’s compare the basic aspects of the water cycle from global and gardening perspectives.
The water cycle starts when the sun heats the surface of the planet. Water on the surface is converted to a gas that rises into the atmosphere. The soil of your garden, your driveway and house, and the concrete of your patio also act as heat islands, absorbing the sun’s heat and causing nearby water to evaporate. This is why it’s a good idea to give potted plants sitting on a concrete patio feet that raise them off the surface enough to allow air to flow. This will keep them cooler and reduce the amount of water they need.
Water held within plants is also released. As they perform photosynthesis, gas exchanges must occur. Water is released into the atmosphere as this happens. The combination of evaporation by heat and transpiration by plants is called evapotranspiration.
As water vapor moves around in the atmosphere, the bits of water vapor bump into each other and grab on. Those clusters of water vapor keep getting bigger, condensing into fog, mist, and clouds. If you’ve ever been to Disney World in August, you know exactly what I mean.
Some plants thrive in misty, foggy, humid environments. Others end up with fungal diseases. If humidity is causing problems in your garden, be sure to prune your plants in ways that provide good airflow.
Water falling to the ground is precipitation. Globally, precipitation may mean rain, snow, hail, or sleet. In your garden, that precipitation may be rain, sprinklers, or a garden hose. As precipitation passes through the atmosphere, it collects particles along the way. Those particles are often car fumes, factory pollution, and dust, and those particles reach your soil right along with the water.
Water passing from the surface into the ground is called infiltration. Once the water has been absorbed by the soil, it is known as groundwater or soil moisture. Just because water is in the ground does not mean it is available to plants. Compacted soil has poor infiltration rates. And water does not spread smoothly through the soil in all directions.
A fellow gardener called me with a zucchini problem. Her plant kept wilting, even though she was watering it regularly. I asked her if the water was reaching the roots. The phone was silent for a moment before she replied, saying she thought so. I had her go check. She called me back a few minutes later astounded. Even though she had been laying the hose next to her zucchini plant, the water was all veering away in another direction once it infiltrated the soil. I had her create an irrigation ring around her zucchini and it grew much better.
Speaking of growing well, infiltration is how minerals get in the water that feeds our plants. As water enters the soil, some minerals are caught in solution. That solution is then absorbed by plants to provide both food and water. Now, some plant nutrients are more mobile than others. Immobile nutrients aren’t actually immobile, they just need a lot more water to move around. Blossom end rot is an example of irregular irrigation causing what looks like a nutrient deficiency. Most gardens on the West Coast of the US have abundant calcium, but may not be watered regularly enough. [Of course, a lab-based soil test is the only way you can learn what’s really in your soil.]
Water moving across the land is called runoff. Surface runoff, or urban drool, is wasteful and potentially dangerous. As suburban sprinklers miss their mark and water streets and sidewalks instead of lawns, they also carry oil, excess fertilizer, trash, and pollutants into waterways. Please make sure your sprinklers water where you think they do and adjust them as needed.
As you can see, the water cycle is a series of steps that pass through various filters along the way. I once had a student create a variety of natural filtering systems for a science project. She used rocks, leaves, sand, and soil in separate containers to filter muddy water. Which material do you think did the best job of cleaning the water?
I thought it would be the rocks, but I was wrong.
It was the soil.
You can grow a surprising amount of food in your own yard. Ask me how!
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