Here in Southern California my local forecast shows another two days of rain coming starting tomorrow morning. Considering the fact California is in a state of serious drought, all rain is welcomed. Last year was to be the year of the drought-breaking El Niño, but that never happened. Earlier this fall a few long-range forecasts guessed for a cold, dry winter for us. Luckily this hasn’t played out. Not only has it been a very warm December (I have yet to see under 40° F), it has also been wet. Very wet. The best part is that these storms have been hitting every 7-10 days. Another plus is that the last three storms have recorded 1 inch or more of rain. It is right about here that my readers from tropical areas start to laugh. But believe it or not, 1 inch of rain is a lot when you consider San Diego averages just over 10 inches of rain each year!
Rain in Southern California is always an exciting event for me. I love to go outside, sit under some cover, pop open a beer and just watch and listen to it come down. A few beers and storms later, I noticed just how green and alive the garden is for late December. I believe it to be thanks to the magical properties of rainwater. Much of these observed “magical properties” have always remained of an anecdotal nature by me. I couldn’t back them up more than what my eyes could observe. After the considerable difference in appearance in my garden this December versus the last few Decembers, I decided to turn anecdotal into fact. Research ensued and now I have a better understanding of what makes up these magical properties of rainwater.
Here are the key properties of rainwater that I was able to come up with during my research.
Rainwater is almost entirely just pure water.
Free of the salts, minerals, treatment chemicals, and pharmaceuticals that are found in municipal tap water. This purity is mostly due to evaporation: nature’s purification process. The process of evaporation leaves the bad behind; things like nasty chemicals and pollutants. Once the rain falls to earth it will pick up stuff like pollution and particulates. So what finally hits the earth isn’t as pure as what went up into the clouds. But unless you live in a really smoggy, polluted area, what is lost through evaporation will always be greater than what the rain picks up from the sky as it is falling.
When looking at rainwater over municipal tap water, remember too that rainwater hasn’t had things like fluoride and chlorine added to it. Worse yet is that most tap water in the US now contains chloramines. They stay in water much longer than chlorine and they are designed to kill all bacteria. These chloramines are the reason you have to treat city water before filling fish tanks or koi ponds. Too much chloramines can’t be good for the beneficial bacteria found in soil.
Rainwater is soft water.
Rainwater is naturally slightly acidic. Most of the plants people grow will prefer a soil pH slightly acidic. Somewhere around a pH of 5.5 to 6.5, where 7.0 is of course neutral. Thanks to Mother Nature, rainwater typically has a pH of 5.7. This is because it is exposed to carbon dioxide in the atmosphere. In some cases the pH can be much lower. Acid rain is an example of this in which industrial pollutants such as sulfur dioxide dissolve in rain water and lower its pH considerably.
Unlike rainwater, municipal tap water is hard water. To protect metal pipes from corroding, your municipal tap water is treated to be alkaline. It can have a pH level upwards of 8.5. My water from Vista Irrigation District (VID) has a pH of 8.2.
Rainwater has Nitrogen.
Not only is rainwater highly oxygenated, it also has another secret beneficial ingredient, one that goes unknown to most. This secret is that rainwater contains nitrogen and it is in forms that plants can absorb. How nitrogen works in the atmosphere is a very complex thing, as the graph below shows. To put it in basic terms, the nitrogen found in the atmosphere came from both natural (wildfires) and human sources (transportation, agriculture and industrial emissions). This nitrogen in rainwater is what gives us the free “fertilizer.” The cleanest way the “fertilizer” is made is when lightning strikes the nitrogen molecules in the air. Some of the now-free nitrogen atoms combine with oxygen to form nitrates that mix with the rain. This process is called atmospheric nitrogen fixation. Truly one of the best magical properties of rainwater.
Atmospheric Nitrogen Pathways (Source: National Science and Technology Council Committee on Environment and Natural Resources, Air Quality Research Subcommittee)
Rainwater leaches out salts in your soil.
In a Mediterranean climate with lower rainfall, such as here in San Diego, soils build up high levels of salts. These salts have accumulated during the driest, hottest months when plants have received the most municipal irrigation. Municipal irrigation is always high in Total Dissolved Solids (salts, minerals and metals that are dissolved in water). Salts also build up in soils from fertilizers. High salt levels can cause things like leaf-tip burn and even death in weak plants. It is very important to leach out these salts from the root zone, so gardeners must periodically deep water their plants. The drought and cost of water here in California make this a very difficult proposition. This is where rain water comes in. Long rainstorms will leach all the accumulated salts out of the soil and pots, making your plant’s roots happier and healthier.
Rainwater saturates your entire garden.
It doesn’t matter how well you planned your irrigation system, you just can’t get uniform watering to your entire garden. It is impossible to replicate rain with your outdoor irrigation system. With irrigation, some areas will inevitably get a lot of water, while others can stay dry. If you are on drip, like many in low rainfall areas, you are only spot watering a part of a plant’s entire root zone. Worse yet, in order to meet drought restriction requirements and save money, many gardeners don’t water long enough to get water to the deeper roots. Dry soils soak up all the water and only the roots in the upper soil levels get the water. When it rains, your entire garden is getting a uniform drenching. Roots that never see irrigated water, now help take it up. Also, with saturated soils your plants stays hydrated for a longer period.
Rainwater literally washes your plants.
Plants collect light and nutrients through their leaves, and through the process of photosynthesis they convert it into the chemical energy they need for growth. In dry areas like here in San Diego, plants accumulate things like litter, dirt, dust and even pollution on their leaves. This buildup can interfere with the absorption of sunlight and nutrients. Rainwater washes all this away, giving your plants a squeaky-clean new start.
The magical properties of rainwater are truly amazing. Nothing we can do will ever replicate rainwater. I only wish we would get more rain here in Southern California. Some years we can go 6-8 months without a single drop of rain. There has been a lot of talk about rainwater harvesting and it is a popular buzzword right now. The subject should warrant its own blog post in the future. Sadly, for me, the Return on Investment (ROI) just doesn’t add up. A unit of water costs me $2.34/mo. One unit of water is 748 gallons of water. I have one acre. You do the math. Until they can find a way to make rain harvesting cost effective here in Southern California, I will just have to feel blessed with every storm we get. Time to get ready for the next one coming tomorrow…
Len, I have been thinking of doing some minimal rain harvesting. I have two plant beds under a roof and many potted plants around the yard.
I am thinking of rerouting some downspouts to drain into the covered beds. Despite my best efforts, those beds do not get salts washed out as well as I would like.
Also thought about putting a couple of cheap plastic barrels on other downspouts to collect a some water for use on potted plants during the summer.
I figure for targeted and limites use that can’t be too expensive can it?
Its perfect for targeted uses. That is what I would put it in for. Greenhouse plants, house plants, succulents in pots, etc. Replacing irrigation doesn’t work for gardens like ours. You will fill rain barrels in minutes with a good storm. It is amazing how much rain comes off your roof.
It also makes sense to capture and retain rain water onsite to the maximum extent possible rather than direct it off site into storm drains. Something I advocate with any new landscape design if it can be safely done without causing flooding, erosion or slope instability. It definitely reduces the amount of irrigation required between rains, or at least at the shoulders of the final rainy period.
I totally agree that ROI is better for using a sustained, continuing all year round source such as gray water in our Mediterranean climate, even though it is trickier to use.
Part of the magic is very simple–the dust is washed off the foliage. Everything looks greener. The agaves and aloes had little mud puddles in the lowest leaves the first couple of rains–so much stuff washed off.
The rain has been wonderful, and now signs of a pineapple express type event for next weekend for some part of California.
I spent a minimal amount on downspout diverters and trash barrels to collect rainwater and channel it to the driest places on the property. It does help.