Monsoon Rains Have Hidden Benefits For Plants

The loud crackle and thunderous boom of lightning is now a familiar sound as our Monsoon season is in full swing! But have you ever noticed that our summer storms bring more than just much needed rainfall? The desert, and plants in general, just seem greener after a thunderstorm. And the reason: with the rain comes a wealth of life giving plant nutrients.

Lightening is a potent fertilizing agent. Every time it strikes, nitrogen in the atmosphere is combined with hydrogen or oxygen to form ammonium and nitrate, two forms of nitrogen. The nitrogen then goes into solution in atmospheric moisture and is washed to the ground in rainfall. Plants then absorb nitrogen from the ground and utilize it for growth. Since it is a key constituent in chlorophyll, the green pigment of plants, nitrogen causes a greening of the plant.

Physicists estimate that roughly 250,000 tons of nitrogen are produced by about 1,800 thunderstorms that occur on Earth every day. Our summer thunder storms can release significant amounts of nitrogen for plant growth here in Tucson. That causes a significant part of the greening of plants we notice after a storm. But other constituents of rain also contribute to this greening!

In theory, rain water is pure. It is formed from evaporation of moisture largely from the ocean, but also from inland bodies of water, the soil, plants, and even animals. Condensation returns it to earth; but not before it picks up some hitch-hikers. Sulfur is one of these. It is possible for rain to provide as much as 40 pounds of sulfur per acre per year. Less in our desert environment, but still when the rains come so too does the sulfur. Sulfur is an important constituent in the formation of plant amino acids.

Dust is something we have no shortage of here in the Southwest, but dust although a nuisance indoors can be beneficial. Dust is often carried thousands of miles on the upper air currents, and comes down to earth during rain storms. Dust carries with it a number of mineral nutrients necessary for plant growth. It also contains beneficial microorganisms which enhance plant growth. The solubilized nutrients can quickly influence the color of foliage. Microorganisms aid in the breakdown of organic compounds into plant nutrients. They also create symbiotic relationships with plant roots which aid in the uptake of nutrients. All this translates into a rapid "green-up" of plants!

The level of soil benefiting elements and microorganisms is related to the origin of such dust. Ashes from forest fires contain potash, an essential plant nutrient. Debris from volcanos, which can travel world-wide contains a wealth of essential minerals for plant growth.

The number of thunderstorms we enjoy in the Tucson area are limited, however the beneficial effects of rainstorms can be bottled; or at least barreled, for later use. Rainwater can easily be trapped and stored for later use. The easiest way is to attach barrels to the down spouts from roof gutters. Large plastic garbage cans work well. Use a dark color, like green or gray, to keep the light out. Keep the lid on tight to keep out light, bugs, and critters. This will keep the water fresh and prevent stagnation from algae and bacteria. Cut a hole in the lid, large enough to put the downspout through and seal the crack with caulking or duct tape. A valved exit pipe at the bottom of the barrel allows you to attach a drip system or hose for irrigating plants. If you want, you can connect several rain barrels to collect more water. PVC piping from the top of one barrel to another will allow water to overflow from the first barrel into the next. You can connect a number of barrels this way. Barrels can be screened with shrubs if appearance is a priority.

During a typical Monsoon season, the roof of an average size house can collect as much as 4,000 gallons of rain water! You can collect as much water as you wish, depending on the number of barrels you use. An overflow pipe well allow the excess to escape. A rule of thumb for the Tucson area is to have one plastic trash container (32 gallon capacity) for each 6 feet length of gutter.

Rainwater does have real benefits for plants. So, if after the next thunderstorm you notice everything looks greener; it's not your imagination! It's just Mother Nature working her special magic.

John Begeman
September, 1998