[Earthling]

Abner Aclan  asked the Naked Scientists:
   
Hello Chris and the rest of the Naked Scientists,

I really love your podcasts [nofollow].

Is my observation correct that the grasses and weeds bloom so nice and fast after a rainy day?What's in the rain that the plants love so much compared to ordinary water?

Thank you once again.

Abner Aclan
Lipa City, Philippines

What do you think?

[Chemistry4me]

More dissolved nutrients.

[Don_1]

As C4M say's, there will be more nutrients in rain water than in tap water. In fact tap water usually contains high levels of calcium which can be positively damaging to some ericacious plants, such as Azaleas, Rhododendrons and Erica (Heather).

Rain also washes the leaves, clearing the pores and allowing them to 'breath' and most plants can absorb some of the nutrients directly through the leaves. See this on foliar feeding. http://en.wikipedia.org/wiki/Foliar_feeding

[Earthling]

Thank you for the replies, but what do you mean by " more dissolved nutrients" in rain water?Isn't tap water has more nutrients or salt in it, thus it has more "plant" food than rain water? Thank you again []

[Chemistry4me]

Tap water has chlorine in it which is deadly to plants. The minerals and pH level of the water will contribute to the soil content, which is the most vital part of the plants environment.

[Earthling]

Granting I have a ground water or I let the tap water stand for 24 hours to let chlorine degenerate.Is not the tap water will have more nutrient than rain water? In my humble opinion, there is more to the rain water than just mineral levels or ph or so.I hope someone out there will give a better explanation. Thank you very much. [] []

[Chemistry4me]

Well Don_1 did mention Foliar Feeding []

Rain also washes the leaves, clearing the pores and allowing them to 'breath' and most plants can absorb some of the nutrients directly through the leaves.

[Earthling]

Do you think the rain has enough plant food(nutrient) in the first place?I am not sure about it but I suspect there is very little dissolved nutrient in it.The foliar thing does not answer the question unless someone give us a data of rainwater analysis.Thank you again for your help.

[Chemistry4me]

Help? I don't think I did that []
Sorry I couldn't help you out a bit more [:I]

[Earthling]

You were a big help...by replying and participating in a discussion, we are helping each other so we will learn more. In fact, some of your points maybe right. We just need to have other people to butt in.The reason why we ask question is because we need to separate the "facts from the quacks". I really appreciate your being here. Thank you very much. [] [] []

[Don_1]

The chemical analysis of rainwater will differ from region to region, but there is more likelyhood of rainwater containing the elements plants need to survive (N, K, P, Mg) than tap water which will contain mostly elements of no real use & some positively damaging.

[Earthling]

That's a problem with rain nowadays because of atmospheric pollution we can't be really sure.But I think it is much better than tap water, isn't it?Perhaps plants bloom better after a rainy day is because aside from those optimal salts that you've mentioned, it is a highly oxygenated that the plants will love it so much.What do you think? I hope there is a study between a fresh rain vs stored rain in relation to plant growth. Thanks a lot.

[Don_1]

The higher oxygen levels in rainwater will certainly benefit plants. A point I should have noted.

I don't know if any study of fresh rain compared to stored rain has been carried out. Might be worth looking to see. I should think different storage methods could have different effects on the water. The comparison would need to be between metal, plastic & wooden butts kept in shade, semi-shade and full sun, covered and uncovered, length of time stored. It could get a bit complex. Then you would need to test actual results on different plant types. A mere biochemical examination might not tell what will happen in practice!

[Bored chemist]

Where do you guys think tap water comes from?

Rainwater is relatively pure water. By the time it has been collected and piped to taps it contains more stuff, not less.
(groundwater is just rain that fell a long time ago).

While it's true that calcium salts in tapwater might be harmful to some plants, the same salts are a nutrient from the point of view of calcium loving plants.
There's not a lot of free chlorine in tap water and the process of spraying it reduces the concentration still further. If the chlorine in tap water was deadly to plants the water companies wouldn't need to call for hosepipe bans in droughts.

Is there any evidence to support the original assertion that rain water affects plants differently from other water?
Similarly, where's the evidence for assertions like this "there is more likelyhood of rainwater containing the elements plants need to survive (N, K, P, Mg) than tap water which will contain mostly elements of no real use & some positively damaging."
I can see how there might be significant nitrogen in rainwater but would someoone care to explain how the K, P and Mg got into the clouds?

"The higher oxygen levels in rainwater will certainly benefit plants. A point I should have noted."
Why? it's not like plants (which generate oxygen) have a shortage of the stuff.


Isn't this meant to be a scientific website?

[Chemistry4me]

[:0] I feel like I've just been slapped in the face [:0]

[Chemistry4me]

Even though he wasn't even talking to me.

[Earthling]

Where do you guys think tap water comes from?

Rainwater is relatively pure water. By the time it has been collected and piped to taps it contains more stuff, not less.
(groundwater is just rain that fell a long time ago).

While it's true that calcium salts in tapwater might be harmful to some plants, the same salts are a nutrient from the point of view of calcium loving plants.
There's not a lot of free chlorine in tap water and the process of spraying it reduces the concentration still further. If the chlorine in tap water was deadly to plants the water companies wouldn't need to call for hosepipe bans in droughts.

Is there any evidence to support the original assertion that rain water affects plants differently from other water?
Similarly, where's the evidence for assertions like this "there is more likelyhood of rainwater containing the elements plants need to survive (N, K, P, Mg) than tap water which will contain mostly elements of no real use & some positively damaging."
I can see how there might be significant nitrogen in rainwater but would someoone care to explain how the K, P and Mg got into the clouds?

"The higher oxygen levels in rainwater will certainly benefit plants. A point I should have noted."
Why? it's not like plants (which generate oxygen) have a shortage of the stuff.


Isn't this meant to be a scientific website?

From the beginning I ask this question if my observation was correct...that plants bloom after a rainy day.Nobody answered me directly and every replies assumed that it is beneficial.It is just my observation and  I don't know if I am correct. I grow up in a farm and I do observed that grasses and weeds grow very well after a pouring rain.Maybe there are other factors and maybe it is not just the rain after all.
Yes, this is a scientific website and in here we ask question so we will know that it is a fact and not a myth.
Chlorine in tap water? We live in different location guys. I assumed that when you say tap water.. it is like our chlorinated city water ( that is tap water to us).No it is not harmful to plants as long as the chlorine level is kept at 4ppm. Now the tap water that you mentioned is actually well water to us, an underground water,river, spring,runoff, etc.and mostly are being drawn up by a pump. No I don't think there are chlorine in this tap water maybe Chlorides.
There are some traces of some elements in rain water now ( not necessarily the one mentioned previously)....maybe you want to see this link

http://www.people.carleton.edu/~bhaileab/EnvironmentalGeology/RainWater.pdf [nofollow]

Please note the presence of Oxygen Isotopes, whether it is significant or not I have no knowledge to answer that.
Yes!! Plants benefits from high oxygen content. The leaves manufacture the oxygen but the roots are the ones needing it. The highly oxygenated root zones will surely benefit the plants as they are also benefited with high CO2 content thru their leaves....ask any hydroponics greenhouse grower and they will attest to this.
I could be wrong but we are here to learn....this is a scientific website, isn't it?

[Don_1]

BC, Sorry, my post is misleading. It does suggest that N, K, P & Mg would be found in rainwater, which, as you state, is not the case, except for N. This was intended as a short list of the more essential elements plants require, not as a list of what might be found in rainwater.

However, I must take issue with you on the matter of acidity & Oxygen.

Plants do need oxygen for cellular respiration. Oxygenated water is a good means of obtaining that oxygen. As for lime preferring plants, the majority of plants prefer soils with a Ph around 6.5. The next largest group are the ericaceous (Acid preferring) plants, which include Azaleas, Rhododendrons, Camellias, Erica’s, Ilex, Hebe’s & most other shrubs, Acer, Magnolia, Pines, many fruit trees & bushes. The smallest group by far are Lime preferring plants, such as Diasicas & Brassicas. In the case of most plants in this group, they are not so much lime preferring as lime tolerant.

Rainwater, being softer than tap water, is less likely to leave a residue on the leaves, allowing them to absorb water and breathe easier. If you have house plants, you will find they will benefit from being put out in light rain during the warmer months. (Except those which do not like getting leaves wet, such as African Violets).

I don’t know if any controlled tests have ever been carried out to compare rainwater to tap water in plant growth, but any horticulturalist will tell you that there garden always grows better after a good watering with rain than a good watering with tap water. I have certainly found this to be the case, and put it down, mainly, to the leaf washing and the fact that tap water can have an adverse effect on soil acidity, even if only temporary. It is worth pointing out that some plants, such as the Azalea family may survive tap water used during one growing season, but will probably die as a result the following year.

[Bored chemist]

Whatever other points may be put forward I think the dominant factor is that rain generally puts down a lot more water than people usually bother to do with a watering can or hose.
Plants like water.
"Plants do need oxygen for cellular respiration. Oxygenated water is a good means of obtaining that oxygen. "
Plants (at least during the day) produce oxygen. In order for that oxygen to escape from the plant the partial pressure of oxygen in the plant must excede the partial pressure outside it (ie in the air). The highest concentration of oxygen that would be present in tap water would be the saturation level (ie saturated with oxygen at 0.21 atmospheres).
The plants contain more oxygen than the water you spray onto them- this is true whether it's rain water or tap water. The olly exceptions would be if you were spraying carefully oxygenated chilled water on a hot day or if you were watering the garden at night.

[Earthling]

I think this will go on and on and on and so many questions will arise.How much is too much water for plant to tolerate? Extended rains for days are known to damage or kill the plants.Not all plants tolerates so much water while others love it.There is so much to know out there.Maybe some plants bloom after a rainy day and why or does it matter if it is a rain or just a tap water. I am still searching for an answer. [] [] []