I figured it might be interesting to revisit the topic of pH and cactus cultivation. There seems to be a lot of voodoo around it. There's a discussion (somewhat heated) right now on Cacti_Etc. about whether or not it makes any difference to lower the pH of the water we water our plants with to 5 or so.
The only thing I notice is that rain water has a marked effect on growth and germination that isn't as apparent after soaking plants with tap water. The tap water here in Tempe has a pH of 8.8. Rain water is roughly 5.
peterb
pH again
pH again
Zone 9
Testing the pH of water isn't hard (I'm claiming that as my pun for the day!). A pool kit probably isn't the best one since it will have a limited pH range and not the one you want, but there are kits out there.
Amazing stuff rainwater. I have observed it do wonderful things for plants but haven't ever been able to reproduce the effects. Not even by using stored rainwater! And certainly not by using water from other sources with added chemicals of any kind. That said, most of the time my plants do great on the soft tapwater we have here.
I haven't been following the cacti_etc discussion but I've participated in other discussions. Mostly I take the "con" position, mostly because the people arguing in favour of acidifying their water claim it cures everything from verrucas to prostate cancer, and all from three drops of pixie juice regardless of what sort of water you are starting out with. I'm a bit of a contrarian
Any attempt to dig deeper into what the initial problems were, what nasty properties their water might have, and what magical reaction may have cured them are met with the usual hurt surprise that anyone could question their epiphany handed down on clay tablets. God forbid you should start wondering whether the results apply equally to different species in different soil types.
Amazing stuff rainwater. I have observed it do wonderful things for plants but haven't ever been able to reproduce the effects. Not even by using stored rainwater! And certainly not by using water from other sources with added chemicals of any kind. That said, most of the time my plants do great on the soft tapwater we have here.
I haven't been following the cacti_etc discussion but I've participated in other discussions. Mostly I take the "con" position, mostly because the people arguing in favour of acidifying their water claim it cures everything from verrucas to prostate cancer, and all from three drops of pixie juice regardless of what sort of water you are starting out with. I'm a bit of a contrarian
Any attempt to dig deeper into what the initial problems were, what nasty properties their water might have, and what magical reaction may have cured them are met with the usual hurt surprise that anyone could question their epiphany handed down on clay tablets. God forbid you should start wondering whether the results apply equally to different species in different soil types.--ian
Yes, it is a sore point for many growers, and not just of cacti. And you're right, rain water straight from the sky is the best...trying to store it or recreate that freshness somehow just never does it the same.
I think there are probably a complex set of variables involved that merge to create a simple-seeming effect.
peterb
I think there are probably a complex set of variables involved that merge to create a simple-seeming effect.
peterb
Zone 9
I just took a look at the book Cacti: Biology and Uses. The chapter on environmental biology mentions nothing about soil or water ph.
They discuss temperature, water, salinity, and gravity and wind. They express their results as changes to net CO2 uptake.
Googling Cactus and PH also turns up nothing meaningful.
I'm not sure I'd say that PH has NO impact on plant growth and cacti in particular, but there doesn't seem to be any (extremely easily found) resources to provide learned guidance.
I'll just hazard a guess and say that if you live in an area with EXTREME ph you might want to consider doing something about it.
I acidify the water that I put on my plants to bring it to around 6, because, like PeterB, my tap water is 8+PH. Ian is absolutely correct though, there's a lot more to water than just PH that will impact the vitality of your plants.
It might be safe to say that the only info you'll get on this subject is anecdotal and should be treated as such.
my 2 cents,
Tim
Tim
They discuss temperature, water, salinity, and gravity and wind. They express their results as changes to net CO2 uptake.
Googling Cactus and PH also turns up nothing meaningful.
I'm not sure I'd say that PH has NO impact on plant growth and cacti in particular, but there doesn't seem to be any (extremely easily found) resources to provide learned guidance.
I'll just hazard a guess and say that if you live in an area with EXTREME ph you might want to consider doing something about it.
I acidify the water that I put on my plants to bring it to around 6, because, like PeterB, my tap water is 8+PH. Ian is absolutely correct though, there's a lot more to water than just PH that will impact the vitality of your plants.
It might be safe to say that the only info you'll get on this subject is anecdotal and should be treated as such.
my 2 cents,
Tim
Tim
My experience with tap water is this:
I believe that what affects more on our plants is chlorine that with time do not allow the roots to absorb forming a layer intorno.Il ph although slightly high 8 does not create damage if we repoting often plants about every three years
. Ph control the use of water is that soil in pots and I have not found large variations over the three years also using water with ph8, measured with digital tools calibrated well.
In the past I used water filtered by a reverse osmosis plant but I did not find any benefits and I returned to water from the tap, my has an average of ph 7,5-8.
The best solution is no doubt rainwater for those lucky enough to be able to collect.
Giovanni.
I believe that what affects more on our plants is chlorine that with time do not allow the roots to absorb forming a layer intorno.Il ph although slightly high 8 does not create damage if we repoting often plants about every three years
. Ph control the use of water is that soil in pots and I have not found large variations over the three years also using water with ph8, measured with digital tools calibrated well.
In the past I used water filtered by a reverse osmosis plant but I did not find any benefits and I returned to water from the tap, my has an average of ph 7,5-8.
The best solution is no doubt rainwater for those lucky enough to be able to collect.
Giovanni.
I have always just used the hose to water my plants due to the lack of rain here at the appropriate times. So Im really interested in this subject, although I still have not started doing anything different as far as watering, mostly because of a lack of time. I have not seen a difference in plants watered with rain water or hose water because it simply doesnt rain when I want it to. 
What could be the difference in water straight from the sky as opposed to stored rain water?
Could it be excess CO2 that disapates as it sits?
Many advanced aquarists inject CO2 to help balance an aquarium full of fish and plants as the plants use it up quickly. Injecting CO2 makes the plants in the aquairium grow like krazy due to the fact that the whole system is closer to natural levels of CO2, nitrogen, and O2.
If plants convert CO2 and nutrients into carbohydrates and oxygen provided there is light to maintain photosynthesis. is it that there is less CO2 in the old rain water / hose water and thats effecting the growth of the plants, or just the difference in Ph?
Now Im not considereing hooking up Co2 injection to my hose, just wondereing if that may be part of the difference you have experienced.
What could be the difference in water straight from the sky as opposed to stored rain water?
Could it be excess CO2 that disapates as it sits?
Many advanced aquarists inject CO2 to help balance an aquarium full of fish and plants as the plants use it up quickly. Injecting CO2 makes the plants in the aquairium grow like krazy due to the fact that the whole system is closer to natural levels of CO2, nitrogen, and O2.
If plants convert CO2 and nutrients into carbohydrates and oxygen provided there is light to maintain photosynthesis. is it that there is less CO2 in the old rain water / hose water and thats effecting the growth of the plants, or just the difference in Ph?
Now Im not considereing hooking up Co2 injection to my hose, just wondereing if that may be part of the difference you have experienced.
Forget the dog...Beware of the plants!!!
Tony
Tony
CO2 is what makes rainwater acidic, even without industrial pollutants that cause acid rain. Water droplets falling through the sky have no more or less dissolved CO2 than rainwater that has stood in a barrel for a week, the gas doesn't escape. One exception would be if your stored water gets hot, hot water holds less CO2 than cold water. Even tapwater contains about the same amount of CO2 as rainwater, but it is nowhere near enough to counteract the minerals in hard water. For that matter, "pure" distilled water is not pH 7 unless you take great care to exclude carbon dioxide after you condense it. If you expose the distilled water to air then it dissolves CO2 and becomes acidic just like rainwater.
--ian
Malcolm Burleigh posted this to Cacti-Etc and I repost it here with his permission. It's interesting stuff! For me anyway.
OK lets start at the top. I am a practicing Ph.D. chemist and I have about
14 or 15 patents. Several of these patents deal with the use of low pH and
divalent cations to deposit chemicals and emulsions onto fibers so I have
been working intimately for the last 20 years on the subject of pH.
I've also been raising cacti since the 50's. I have been a member of the
CSSA since 1972. I raise many plants and though most of my cacti are from
the Chihuahuan Desert they actually don't consume that much water compared
to my succulents, leafy tropicals and tomatoes. For this reason, I drop the
pH of all my water to ca. 5.5 and water the plants with this water. It would
save a bit on acid but that's not an issue for me. I also add fertilizer
into the water. I am not sure why my plants seem to respond so well to low
pH water. I have done this for all of my plants and the results are quite
amazing. The Chihuahuan species, my Stapeliads, and the rest of my summer
outdoor tropicals are doing amazingly well. Before this they were just OK
and I had to repot frequently.
I also raise and have tried in the past to raise many of the small ferns
that you find in the desert and other dry environments. Cheilanthes,
Pellaea, Notholaena as well as the fern allies such as Selaginella all
evaded my attempts to keep them alive. Sedum integrifolium, Dudleya etc.
also evaded my attempts. At first I blamed the smog in Southern California,
where I lived at the time. But there were Dudleyas living in smoggier areas
than my garden in Riverside CA. When I moved to St. Paul MN, I then had to
blame the chlorine in the water. I can tell you now that these plants are in
my garden and living and growing very well on low pH water! I don't know
what the pH of the Riverside CA water was but here in St Paul it is 9.0! I
didn't realize that for some time and so I'm trying to tell others that don't
water with rainwater that their water may be a serious problem to their
horticultural success.
Limestone soil issues -- My target plants were and still are Escobaria and
Turbinicarpus. I had been having trouble growing these plants in the normal
peat moss etc soil. I could graft that very well but on their own roots they
didn't shine for me. My inspiration was jogged in 1998 by the article of
Ralph Peters in the CSJ 70-1 (pp10) recommended a zero organic soil. Ralph
is right. These plants are growing in rock, solid vertical rock ledges and
benches. Under no circumstances would anyone think of this as "soil". The
normal response is to ask -" Wow! why are they growing there?". I could say
that they like it there but I will say that they are remarkably adapted to
this existence. I have been traveling in that desert for many years and
actually seeing these plants, where and how they grow.
People who visit these deserts see this and are amazed. Yet they return home
and continue to use their "cactus" potting mix with loads of organic leaf
mold, black dirt and peat moss with a few sprinkles of perlite. Then they
wonder why they have problems with Sclerocactus, Pediocactus, Mammillaria
tetrancistra and the other deep desert species. These plants take poorly to
this treatment. Then you hear that these plants are "difficult"! They are
tricky but they are not difficult. Their needs are just quite out of the
ordinary.
Here is what I do - Limestone plants -- Since I knew these plants grew on
limestone, I decided that I would repot my plants with our local dolomite. I
don't exactly add Dolomite to my Chihuahuan Desert species. Rather dolomite
is the soil for these plants! There is a type of crushed rock that is sold
cheaply around here for about $2.25 for a 5 gal bucket. It is called Class
5, \276 minus Dolomite. Normally it is used for putting on cheap driveways. It
contains all the rock that is less than \276 in. (2cm) in diameter. I have
screens that are 1/2in, 1/4in, 1/8in and window screen. I screen out the
large >1/2in rock and save the rest. I use the \275-1/4 for top dressing and
keep the \274 - 1/8 for my soil. My plants, especially the Turbis that easily
lose their seeds now have seedlings growing from them.
I take this "soil" material and wash it thoroughly in a large box with
window screen in order to remove the fines. What remains is then my soil. I
often mix it with perlite, of the same mesh size since some of my pots get
too heavy to carry. I have to bring all of my plants inside due to our
extreme winters. (with a few exceptions.)
My non-limestone species get a similar treatment but with a local igneous
ground rock from Dresser WI. It is used in places to hold down the soil. But
they also sell the <1> H2CO3 (or hydrated CO2)
(biarbonate) -->(bisulfate)
The function p is defined as the negative log. (Log100=2 so p100= -2)
The equilibrium constant for this reaction is Ka = 4.26X10-7. And the pK
value is 6.37 as listed in the Handbook of Chemistry and Physics. The
Equilibrium equation is defined as. The values in parentheses are the
concentrations of the individual species in the water.
((HCO3)-) x (H+)/ H2CO3 = 4.26X10-7= Ka
As bisulfate is put into the water the concentration of bicarbonate ion is
diminished and the concentration of dissolved CO2 increases, Applying this
to the reaction the concentration of bicarbonate becomes 0.760-0.638meq/li =
0.122meq/li and the CO2 becomes 0.638meq/li.
Plugging that into the formula and then solving for the concentration of H+.
Then taking the negative log. We come out with a pH of 5.65. Cute? But I
already know this because I measured it about 2 years ago.
Now lets get onto the reaction of this rainwater with the limestone because
I wondered about that also. This reaction as Tomasz suggests is rather slow.
The water in these summer thunderstorms comes through and quickly washes the
solubles away. The pH of the water starts out low and gradually increases to
somewhere below 7. At a pH of 7, about 80% of the CO2 has been converted
into bicarbonate. It appears to take about 48 hours with dolomite. This
reaction is basically controlled by the surface area of the limestone rock.
This is why I wash out my fines. It also gives me the excellent drainage
they need. I suspect that these plants are simply adapted to higher pH than
non-limestone plants but this is not to suggest that a pH in excess of 8 is
healthy for them.
There is an Orchid here in parts of the mid-west that only grows in
calcareous fens, Cypripedium candidum. The rest of its Cypripedium relatives
are only found in acidic bogs. This would suggest that it is possible for a
plant to quickly adapt to these higher pH conditions. If you are raising
cacti it would be a good idea to have some data about where the seeds are
from.
The reaction of Calcium Hydroxide to form Calcium Carbonate is the one that
Mac Clarke mentioned. In this case you start at a very high pH using the
soluble Calcium Hydroxide (Slaked Lime). You blow with a straw into the lime
water and gradually you create a cloudy suspension of Calcium Carbonate with
the CO2 in your breath.
Ca++ + 2(OH)- + CO2 --> CaCO3 + H20
However, as you continue blowing, the Calcium Carbonate, that you created
previously, will further react with the CO2 in your breath and dissolve as
Calcium Bicarbonate is created.
CaCO3 + H2O + CO2 --> Ca++ + 2(HCO3)-
This latter reaction is why limestone rocks have all the fissures and
cracks, since the rainwater slowly over the course of time does the same
reaction.
Calcium Bicarbonate is generally the source of hardness in the water.
Heating this water will cause the equilibrium to shift and for CO2 to be
expelled from the water. You may see this on teakettles and in hot water
pipes. The scale(CaCO3) will dissolve in vinegar and cause some fizzing as
the CO2 is released.
Further heating of Calcium Carbonate will cause the rest of the CO2 to be
released and the end product is Calcium Oxide.
CaCO3 --> CaO + CO2
When this is reacted with water it forms Calcium Hydroxide and you are back
to the start.
CaO + H2O --> Ca++ + 2(OH)-
An aside - "Lime" is a confusing word. There is Lime, which is Calcium
Oxide. There is slaked lime, which is Calcium Hydroxide and there is
Limestone which is Calcium Carbonate. Never add the first two to your soil
they are toxic and also caustic! Oh yes! there is also a nice fruit which is
good when rubbed on the mouths of Mexican Beer Bottles. Yum-yum! Low pH too!
These deserts can be very harsh climates. Droughts have been known to last
for decades. There is ample evidence for very severe droughts in the west
around 1000 AD and in the later 1200's. The collapse and disappearance of
the Mimbres and Anasazi civilizations attests to how dry this can be. The
drought in the late 1200's lasted as long as 100 years! The people of the
American West may be in for a big surprise some day!
The desert "soil" here after 3-4 years of no rain can be quite dry and free
of any water. In many instances the plants disappear from the landscape.
What remains are the seeds which can last for many years. When and if the
drought breaks, these seeds can quickly grow. It is not an exaggeration to
say that a cactus may spend most of its life as a seed!
A case in point is a colony of Mammillaria tetrancistra in the Newberry Mts.
of Southern Nevada. During the early 80's, I traveled there quite
frequently. These plants grow on the granite outcrops in a small area in
these mountains. As the years passed the drought of the 80's took its toll
on these plants and finally the only place they could be found were just the
tops of the granite outcrops and very few plants at that. Finally the
drought broke in the early 90's and when I visited in '93, many were back
and growing nicely. They were all quite small. I think that is why people
will say that they found a bunch of small tetrancistra and think that is
their habit to stay small. What I'm getting at is that the amount of water
and the pH that the cacti experience varies wildly. These plants are really
growing on the edge of existence.
The water in many municipal supplies is often artificially adjusted upward.
The reason is that this protect the pipes from corrosion, which can readily
happen with low pH. In many of the older cities such as St. Paul much of the
pipe is still lead. So they have even more reason to keep the pH high here.
It is kept around 9.0 as long as I have followed it. The alkalinity of our
water is also controlled. This is probably more important for me than the
actual pH.
The alkalinity in various places can vary a lot. Before you start adjusting
your pH you should have some knowledge of the pH and the alkalinity. So to
begin with you need a pH meter. But the good ones sell for at least $150.
This is a lot to spend for a problematical issue. You don't know if it's
broken so you don't fix it.
A much better solution is to purchase a pH indicator kit. Fortunately there
is a group of people who are much more technically advanced than we cactus
growers are. These are the hydroponics people and you can purchase a kit for
about $6-8 from a hydroponics store. General Hydroponics and Sunleaves sell
the two I know of. They are small bottles and a plastic 5cc test tube to
measure the pH of your water. The color gamut goes from 4(red) 6(yellow) to
8(blue). 5.5 is a peachy color.
Take a bucket of your water and start putting measured amounts of acid into
your water. Until you either get the right color with your indicator. For
most people, the best acid to start with is 5% vinegar. It is safe and
readily available. The initial pH will tell you the pH of your water and how
much acid it takes to drop the pH will tell you about your alkalinity. But
don't add any oxalic acid to your water or soil if you want to keep any of
your important trace minerals such as iron, copper, manganese, zinc etc. it
will sequester all of them. There are water sources I'm aware of which
contain almost 10x the amount of alkalinity. In these cases you may want to
either consider either reverse osmosis or citric acid which will render the
calcium salt soluble. Calcium Sulfate, the reaction product of bisulfate and
calcium is only soluble in water to 0.2%. This will cause deposits to form
on your plants.
The hydroponics people generally use phosphoric acid to adjust their pH and
sometimes you will see nitric acid for sale. In addition to this there are
several fertilizers which are pH balanced. I would be careful of them since
they are often not what they claim. MiracleGro is one of these. The pH of
all of the MG products winds up at 6.8 for the recommended addition, even
Miracid. Also you might as well forget Sulfur. This might be good for
temperate plants but cactus soil normally does not have the right bacteria
to convert the sulfur to acid. I have found it easier to add acid and
fertilizer in rather than trying to adjust the pH with phosphoric acid and
then trying to get my NPK amounts correct.
One more thing and this gets back to the original question. If you drop the
pH of your high pH water you may also want to lower the amount of fertilizer
you give your plants. Too quick growth in these normally slow growing plants
will often cause splitting. I have this on a few of my spherical plants now.
Grafting though will cause a lot more splitting.
Malcolm Burleigh
OK lets start at the top. I am a practicing Ph.D. chemist and I have about
14 or 15 patents. Several of these patents deal with the use of low pH and
divalent cations to deposit chemicals and emulsions onto fibers so I have
been working intimately for the last 20 years on the subject of pH.
I've also been raising cacti since the 50's. I have been a member of the
CSSA since 1972. I raise many plants and though most of my cacti are from
the Chihuahuan Desert they actually don't consume that much water compared
to my succulents, leafy tropicals and tomatoes. For this reason, I drop the
pH of all my water to ca. 5.5 and water the plants with this water. It would
save a bit on acid but that's not an issue for me. I also add fertilizer
into the water. I am not sure why my plants seem to respond so well to low
pH water. I have done this for all of my plants and the results are quite
amazing. The Chihuahuan species, my Stapeliads, and the rest of my summer
outdoor tropicals are doing amazingly well. Before this they were just OK
and I had to repot frequently.
I also raise and have tried in the past to raise many of the small ferns
that you find in the desert and other dry environments. Cheilanthes,
Pellaea, Notholaena as well as the fern allies such as Selaginella all
evaded my attempts to keep them alive. Sedum integrifolium, Dudleya etc.
also evaded my attempts. At first I blamed the smog in Southern California,
where I lived at the time. But there were Dudleyas living in smoggier areas
than my garden in Riverside CA. When I moved to St. Paul MN, I then had to
blame the chlorine in the water. I can tell you now that these plants are in
my garden and living and growing very well on low pH water! I don't know
what the pH of the Riverside CA water was but here in St Paul it is 9.0! I
didn't realize that for some time and so I'm trying to tell others that don't
water with rainwater that their water may be a serious problem to their
horticultural success.
Limestone soil issues -- My target plants were and still are Escobaria and
Turbinicarpus. I had been having trouble growing these plants in the normal
peat moss etc soil. I could graft that very well but on their own roots they
didn't shine for me. My inspiration was jogged in 1998 by the article of
Ralph Peters in the CSJ 70-1 (pp10) recommended a zero organic soil. Ralph
is right. These plants are growing in rock, solid vertical rock ledges and
benches. Under no circumstances would anyone think of this as "soil". The
normal response is to ask -" Wow! why are they growing there?". I could say
that they like it there but I will say that they are remarkably adapted to
this existence. I have been traveling in that desert for many years and
actually seeing these plants, where and how they grow.
People who visit these deserts see this and are amazed. Yet they return home
and continue to use their "cactus" potting mix with loads of organic leaf
mold, black dirt and peat moss with a few sprinkles of perlite. Then they
wonder why they have problems with Sclerocactus, Pediocactus, Mammillaria
tetrancistra and the other deep desert species. These plants take poorly to
this treatment. Then you hear that these plants are "difficult"! They are
tricky but they are not difficult. Their needs are just quite out of the
ordinary.
Here is what I do - Limestone plants -- Since I knew these plants grew on
limestone, I decided that I would repot my plants with our local dolomite. I
don't exactly add Dolomite to my Chihuahuan Desert species. Rather dolomite
is the soil for these plants! There is a type of crushed rock that is sold
cheaply around here for about $2.25 for a 5 gal bucket. It is called Class
5, \276 minus Dolomite. Normally it is used for putting on cheap driveways. It
contains all the rock that is less than \276 in. (2cm) in diameter. I have
screens that are 1/2in, 1/4in, 1/8in and window screen. I screen out the
large >1/2in rock and save the rest. I use the \275-1/4 for top dressing and
keep the \274 - 1/8 for my soil. My plants, especially the Turbis that easily
lose their seeds now have seedlings growing from them.
I take this "soil" material and wash it thoroughly in a large box with
window screen in order to remove the fines. What remains is then my soil. I
often mix it with perlite, of the same mesh size since some of my pots get
too heavy to carry. I have to bring all of my plants inside due to our
extreme winters. (with a few exceptions.)
My non-limestone species get a similar treatment but with a local igneous
ground rock from Dresser WI. It is used in places to hold down the soil. But
they also sell the <1> H2CO3 (or hydrated CO2)
(biarbonate) -->(bisulfate)
The function p is defined as the negative log. (Log100=2 so p100= -2)
The equilibrium constant for this reaction is Ka = 4.26X10-7. And the pK
value is 6.37 as listed in the Handbook of Chemistry and Physics. The
Equilibrium equation is defined as. The values in parentheses are the
concentrations of the individual species in the water.
((HCO3)-) x (H+)/ H2CO3 = 4.26X10-7= Ka
As bisulfate is put into the water the concentration of bicarbonate ion is
diminished and the concentration of dissolved CO2 increases, Applying this
to the reaction the concentration of bicarbonate becomes 0.760-0.638meq/li =
0.122meq/li and the CO2 becomes 0.638meq/li.
Plugging that into the formula and then solving for the concentration of H+.
Then taking the negative log. We come out with a pH of 5.65. Cute? But I
already know this because I measured it about 2 years ago.
Now lets get onto the reaction of this rainwater with the limestone because
I wondered about that also. This reaction as Tomasz suggests is rather slow.
The water in these summer thunderstorms comes through and quickly washes the
solubles away. The pH of the water starts out low and gradually increases to
somewhere below 7. At a pH of 7, about 80% of the CO2 has been converted
into bicarbonate. It appears to take about 48 hours with dolomite. This
reaction is basically controlled by the surface area of the limestone rock.
This is why I wash out my fines. It also gives me the excellent drainage
they need. I suspect that these plants are simply adapted to higher pH than
non-limestone plants but this is not to suggest that a pH in excess of 8 is
healthy for them.
There is an Orchid here in parts of the mid-west that only grows in
calcareous fens, Cypripedium candidum. The rest of its Cypripedium relatives
are only found in acidic bogs. This would suggest that it is possible for a
plant to quickly adapt to these higher pH conditions. If you are raising
cacti it would be a good idea to have some data about where the seeds are
from.
The reaction of Calcium Hydroxide to form Calcium Carbonate is the one that
Mac Clarke mentioned. In this case you start at a very high pH using the
soluble Calcium Hydroxide (Slaked Lime). You blow with a straw into the lime
water and gradually you create a cloudy suspension of Calcium Carbonate with
the CO2 in your breath.
Ca++ + 2(OH)- + CO2 --> CaCO3 + H20
However, as you continue blowing, the Calcium Carbonate, that you created
previously, will further react with the CO2 in your breath and dissolve as
Calcium Bicarbonate is created.
CaCO3 + H2O + CO2 --> Ca++ + 2(HCO3)-
This latter reaction is why limestone rocks have all the fissures and
cracks, since the rainwater slowly over the course of time does the same
reaction.
Calcium Bicarbonate is generally the source of hardness in the water.
Heating this water will cause the equilibrium to shift and for CO2 to be
expelled from the water. You may see this on teakettles and in hot water
pipes. The scale(CaCO3) will dissolve in vinegar and cause some fizzing as
the CO2 is released.
Further heating of Calcium Carbonate will cause the rest of the CO2 to be
released and the end product is Calcium Oxide.
CaCO3 --> CaO + CO2
When this is reacted with water it forms Calcium Hydroxide and you are back
to the start.
CaO + H2O --> Ca++ + 2(OH)-
An aside - "Lime" is a confusing word. There is Lime, which is Calcium
Oxide. There is slaked lime, which is Calcium Hydroxide and there is
Limestone which is Calcium Carbonate. Never add the first two to your soil
they are toxic and also caustic! Oh yes! there is also a nice fruit which is
good when rubbed on the mouths of Mexican Beer Bottles. Yum-yum! Low pH too!
These deserts can be very harsh climates. Droughts have been known to last
for decades. There is ample evidence for very severe droughts in the west
around 1000 AD and in the later 1200's. The collapse and disappearance of
the Mimbres and Anasazi civilizations attests to how dry this can be. The
drought in the late 1200's lasted as long as 100 years! The people of the
American West may be in for a big surprise some day!
The desert "soil" here after 3-4 years of no rain can be quite dry and free
of any water. In many instances the plants disappear from the landscape.
What remains are the seeds which can last for many years. When and if the
drought breaks, these seeds can quickly grow. It is not an exaggeration to
say that a cactus may spend most of its life as a seed!
A case in point is a colony of Mammillaria tetrancistra in the Newberry Mts.
of Southern Nevada. During the early 80's, I traveled there quite
frequently. These plants grow on the granite outcrops in a small area in
these mountains. As the years passed the drought of the 80's took its toll
on these plants and finally the only place they could be found were just the
tops of the granite outcrops and very few plants at that. Finally the
drought broke in the early 90's and when I visited in '93, many were back
and growing nicely. They were all quite small. I think that is why people
will say that they found a bunch of small tetrancistra and think that is
their habit to stay small. What I'm getting at is that the amount of water
and the pH that the cacti experience varies wildly. These plants are really
growing on the edge of existence.
The water in many municipal supplies is often artificially adjusted upward.
The reason is that this protect the pipes from corrosion, which can readily
happen with low pH. In many of the older cities such as St. Paul much of the
pipe is still lead. So they have even more reason to keep the pH high here.
It is kept around 9.0 as long as I have followed it. The alkalinity of our
water is also controlled. This is probably more important for me than the
actual pH.
The alkalinity in various places can vary a lot. Before you start adjusting
your pH you should have some knowledge of the pH and the alkalinity. So to
begin with you need a pH meter. But the good ones sell for at least $150.
This is a lot to spend for a problematical issue. You don't know if it's
broken so you don't fix it.
A much better solution is to purchase a pH indicator kit. Fortunately there
is a group of people who are much more technically advanced than we cactus
growers are. These are the hydroponics people and you can purchase a kit for
about $6-8 from a hydroponics store. General Hydroponics and Sunleaves sell
the two I know of. They are small bottles and a plastic 5cc test tube to
measure the pH of your water. The color gamut goes from 4(red) 6(yellow) to
8(blue). 5.5 is a peachy color.
Take a bucket of your water and start putting measured amounts of acid into
your water. Until you either get the right color with your indicator. For
most people, the best acid to start with is 5% vinegar. It is safe and
readily available. The initial pH will tell you the pH of your water and how
much acid it takes to drop the pH will tell you about your alkalinity. But
don't add any oxalic acid to your water or soil if you want to keep any of
your important trace minerals such as iron, copper, manganese, zinc etc. it
will sequester all of them. There are water sources I'm aware of which
contain almost 10x the amount of alkalinity. In these cases you may want to
either consider either reverse osmosis or citric acid which will render the
calcium salt soluble. Calcium Sulfate, the reaction product of bisulfate and
calcium is only soluble in water to 0.2%. This will cause deposits to form
on your plants.
The hydroponics people generally use phosphoric acid to adjust their pH and
sometimes you will see nitric acid for sale. In addition to this there are
several fertilizers which are pH balanced. I would be careful of them since
they are often not what they claim. MiracleGro is one of these. The pH of
all of the MG products winds up at 6.8 for the recommended addition, even
Miracid. Also you might as well forget Sulfur. This might be good for
temperate plants but cactus soil normally does not have the right bacteria
to convert the sulfur to acid. I have found it easier to add acid and
fertilizer in rather than trying to adjust the pH with phosphoric acid and
then trying to get my NPK amounts correct.
One more thing and this gets back to the original question. If you drop the
pH of your high pH water you may also want to lower the amount of fertilizer
you give your plants. Too quick growth in these normally slow growing plants
will often cause splitting. I have this on a few of my spherical plants now.
Grafting though will cause a lot more splitting.
Malcolm Burleigh
Zone 9
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CoronaCactus
- Posts: 10421
- Joined: Thu May 24, 2007 6:16 pm
- Location: Corona, California USA [Zone 10]
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Since this thread is called PH again, I don't know someone already said this but...
Elton Roberts has been advocating using 1 Tb. vinegar to 5 gallons of tap water for the last few years. He is in an area that has water that is quite high in PH. He had plants that were either dying or not growing for years. Well if you ever go to his nursery he is more than happy to show some of the plants that were not growing and since he now acidifies his water, he can show you where they are now starting to grow over the older part of the plant with nice new growth. Although I have lower than neutral well water, last year I started using his method on some stuff of mine that had not grown in a few years and was amazed to see that it seemed to make a difference and they started pumping up and growing. He says repotting will over-ride the Ph thing, but will be shortlived if the plant continues to receive the high PH water(and if you see how many plants he has,you'd rather change the PH of your water than repot every year!).I've also been following this thread on Cacti_etc and found Mr. Burleigh's entry this morning quite interesting.
For what its worth.
Chris
Elton Roberts has been advocating using 1 Tb. vinegar to 5 gallons of tap water for the last few years. He is in an area that has water that is quite high in PH. He had plants that were either dying or not growing for years. Well if you ever go to his nursery he is more than happy to show some of the plants that were not growing and since he now acidifies his water, he can show you where they are now starting to grow over the older part of the plant with nice new growth. Although I have lower than neutral well water, last year I started using his method on some stuff of mine that had not grown in a few years and was amazed to see that it seemed to make a difference and they started pumping up and growing. He says repotting will over-ride the Ph thing, but will be shortlived if the plant continues to receive the high PH water(and if you see how many plants he has,you'd rather change the PH of your water than repot every year!).I've also been following this thread on Cacti_etc and found Mr. Burleigh's entry this morning quite interesting.
For what its worth.
Chris
I guess technically my "less than neutral" is acidic,but since it is at 6.8, it is a far cry higher than normal rain water. Since I live in an area that almost never gets summer rain fall and don't get the pleasure of putting my plants out for a little summer rain, I thought I'd give Elton's vinegar thing a try when he asked me to. I was only reporting a little of what I noticed here. No different than advocating pumice vs perlite or peat vs no peat.
Chris
Chris