Pelecyphora aselliformis, pots, clay pots

[Karsty]

Reading about pH in limestone soils... I use rainwater here which I have tested with Johnson's pH indicator, and it comes up as Ph 5.5. Maybe that is why my cacti are mainly doing well? (the only negative is the P. aselliformis doesn't flower)

The weird thing is, we have hard water here, we get limescale, but the pH of the water in my flat is acid. It's quite a mystery.

[adetheproducer]

The lack of flowering could be the result of the damage to the roots. They dehydrate at the pot edges well before the core of the soil will dry. You then water because the pot appears dry so then you have wet dead ends of roots. This would then mean the plant is expending energy for root production to take up the water and increased immune response to cope with the wet rotting organic material left over from the dead roots all this extra energy takes away from flower production which is expensive in a survival fight. I understand you will want the plant and pot to look good but how great is a dead or dying plant in a pretty pot(excuse my extremity I am not insinuating your plant is dying but you get the idea). There are several things you can try. The easiest would be to seel the inside of the pot with a good varnish. Yacht varnish is good as it's very durable and water proof. It turns your pot into a plastic pot. Also using a fully glazed and fired clay pots, these are nonporous and act the same way as plastic pots. A good source of glazed and fired pots are bonsai tree pots and can be very asthetically pleasing and readily available in most garden centres, ebay is a pretty good source for them too look for stoneware. Here is the sort if pot I mean

20160825_105847.jpg (56.88 KiB) Viewed 2038 times

This one stays outside through summer as well so I keep it in a pretty pot as I look at the pot more than I see the pots in the green house all packed tightly together. It's a non-porous stoneware rather than earthenware and the glaze fills the inside of the pot. These pots do have great advantages. They dry from top and bottom evenly which helps maintain healthy roots, they are also cooler than plastic pots which again is good for the roots which don't like being hot.

Check out Steve Johnson's thread in the members section he has moved to glazed and fired pots and his plants look great and are clearly growing well

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[kristian_Fossmo]

The weird thing is, we have hard water here, we get limescale, but the pH of the water in my flat is acid. It's quite a mystery.

Not really a mystery, "hard water" is water with much dissolved minerals, acidic water is water with hight amount of [H+] or hydrogen protons, so it is two totaly different things. I know it is a common thing to think that the to is linked... hard water if often linked to high buffer capacity, thus withstand acidification very well.

[Karsty]

Many thanks Ade.

I think you are saying good things. I just need to be finally convinced, why do the outer root hairs die because of dryness, but the inner root hairs do not? What's the difference? If what you are saying is really 100% true, I think the idea of sealing the inside of the pot is fantastic

Hey Kristian,

Thanks for your input.

I'm just not quite sure, could you clarify? Are you saying water with an acid pH can be hard because it has minerals dissolved in it?

Just 2 miles away at my mother's house, many years ago, I tested the water and it came up about pH 10 ! I could barely believe it, but every time I tested it it was the same.

Thanks folks, this is fascinating.

[adetheproducer]

The tips dry and the main roots don't because the porous clay pots dry from outside edges inwards but the centre never really thoroughly dry right to the centre, maybe only after the winter rest when there has been months of drying. With sealed or plastic pots the water can only go 2 directions up or down so slower drying times but more even movement of water through drainage and evaporation. The roots are not attracted to the side of the pot as water does not move in that direction it only goes up and down so roots are left sucking up the water in the centre of the pot and lower. As I mentioned earlier the center of the pot will not really dry out 100%, stones will hold water in microscopic cracks and pours even after months of heat in the hottest deserts of the world so a pot in the humid uk will really never dry out. Cacti are specialist of sucking up these hiden water reservoirs. In nature deserts dry out top soil up and in cooler nights the water table will move water up into the soil dried by day so the next day the wetter soil then dries and the roots then needs to reach down to the lowering water table so they evo lved to follow the water. They don't know they are in a pot so the roots follow the water to the pot edges. In the wild soil will dry far more evenly and the roots are not impeded by a clay wall they can just keep on growing. With potted cacti i have found the trick seems to be giving up pre conditions of plant care. I started with clay pots but the plants struggled I made the move to plastic and pure mineral and am getting great results lots of flowers.

[Karsty]

Hi Ade,

Are you saying that the edges of a clay pot get super-dry and that is what causes death of root hairs? I honestly don't mean to be awkward, but surely in a semi-desert or desert the soil, the places where the roots are does get fully dry, otherwise the cacti would never shrivel?

Or do the cacti move water back into the roots and that's why they shrivel? But the edges of a clay pot get so dry that the plant is not able to compensate for it?

[adetheproducer]

Yes it's an in ability to compensate quick enough. In nature evaporation will only occur from the top down so soil surface first then lower depths after. In a clay pot the entire root ball is exposed to evaporation through the pot from all sides so it dries much much quicker than the roots can deal with .

[DaveW]

"If root hairs attached to the inside of the clay pot dry out and die as the pot dries, then what happens to the rest of the root hairs inside the pot when it dries out fully??"

Regarding the fine root hairs on cacti in a drought. It was found in the case of Carnegia's that the fine root hairs are lost in drought conditions as a means of water conservation to save having to use their sap to keep them turgid, but they could regenerate within 24 hours of receiving rain again, Therefore fine root hair loss is normal for terrestrial cacti in times of water stress, but unlike "normal" plants they can quickly regenerate again when water becomes available.

Generally speaking plants in clay pots (unlike plastic or non porous glazed pots) do not produce much root in the centre until heavily pot bound, they are more evenly distributed throughout the soil in non porous ones. Not all clay pots are porous either though they may look so. It depends on how high a temperature the pot was fired at. Most so called frost proof clay pots are not porous since they were fired at a high temperature to make them non porous because it is water trapped in the pot wall that freezes and expands that breaks clay pots in a frost.

A good scientific article on the matter here. You have to double click on the pages to enlarge:-

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC439145/" onclick="window.open(this.href);return false;

Again there are a lot of old gardeners myths which seem logical, but are not scientifically accurate surrounding clay pots.

[kristian_Fossmo]

Hey Kristian,

Thanks for your input.

I'm just not quite sure, could you clarify? Are you saying water with an acid pH can be hard because it has minerals dissolved in it?.

Yes, if it is ions that are not involved with the buffer capacity (or the amount of acidification is high) it is possible to have hard water with low pH. But usually hard water have good buffer capacity and can "absorb" the H+ ions, thus reducing the amount of "free" H+ that effects the pH. pH=-log[H+]

This is a good channel on youtube I think: https://www.youtube.com/user/khanacadem ... +chemistry" onclick="window.open(this.href);return false; has a lot of nice, well explained, videos on many topics

[iann]

That living rocks quote is garbage, chemically and botanically. It is a shame that it keeps getting quoted.

You don't have to grow in clay pots, or any other porous pot, but it can save beginners (or occasionally experts!) from a few bouts of overwatering. Then they become a pain, drying out too fast in really good growing conditions, overheating the roots, causing salt buildup, and generally a whole host of problems that used to be considered par for the course but are now seen as self-inflicted. So if you need to use a clay pot, consider glazing it on the inside, or look out for the problems that they might bring. Consider using a more moisture-retentive mix than you would in a plastic pot (if you've ever grown in a plastic pot!), flush occasionally with plain water, preferably rainwater. Large clay pots are more successful than small ones. Use a top -dressing to help keep some water in the soil. But don't be afraid to let the pots dry out! Cactus roots are designed to grow, then stop growing, then branch and grow again. If you keep them wet constantly then sooner or later you will kill them, and depending on the species that could kill the whole plant.

[iann]

I'm sceptical about the acidic hard water. Not that it isn't possible, but almost all municipal water supplies are deliberately made alkaline if they are not already alkaline.

Water can be considered hard from dissolved minerals other than carbonates, and then will not be alkaline. Things like calcium and magnesium sulphates are common. They are the ones called permanent hardness because they don't break down when you boil the water. So this type of hardness doesn't fur up your kettle, although you can still taste it and will still get soap scums. Unless there are other chemicals in the water, the pH will be determined by dissolved carbon dioxide and is likely to be near 5.5.

The carbonates are alkaline, usually calcium and magnesium carbonate in hard water. Boiling forces them out of solution and they form scales on the nearest surface. You are left with softer water and a mess in your pipes, boiler, or kettle. The idea that they aren't soluble is a farce, but solubility varies strongly with pH and unless they are reacting with acid in the water the solubility is effectively limited when the pH goes above about 8. They are nowhere near as soluble as something like table salt. You may have massive amounts (many millionths!) of dissolved minerals or only a bit, but the pH of hard water will nearly always be between 7.5 and 8.5. Soil too, effective pH even in limestone-dominated rarely exceeds 8.5 or so. Higher pHs usually indicate sodic soils - sodium carbonate or hydroxides are much more soluble and will produce much higher pHs.

If you don't already have carbonates in your water, then the water company probably adds sodium carbonate or sodium hydroxide to make the water slightly alkaline to prevent corrosion in metalwork. Water in pipes has limited access to carbon dioxide and even quite small amounts of these chemicals will keep the water alkaline until you take it out. After standing for some time, being shaken, or just passing through the aeration devices on some taps, you may end up with acidic water again. Nice for the plants

[Karsty]

Hi Iann,

Many thanks for your comments.

I just now let the cold water run for a bit (there's no aeration device) then tested it immediately as it was running out of the tap. pH 6.5. And I get scale here.

Never has it been more truly said, the more you get to know, the more you realise you don't know!

What, exactly, is the living rocks quote that is garbage? I must have missed it along the way.

I've just successfully germinated (nearly) ten Welwitschia seeds which were apparently wild-sourced. What kind of intricate convoluted moisture/dryness/pH/differences in water movement, nevermind light levels and temperature adventures I'm going to have with these, who knows? Perhaps that's for another thread. Is Welwitschia relevant in this forum? I grew some successfully many years ago, until I let them dry out. That killed them point blank.

From now on I will be painting the inside of my clay pots with yacht varnish if they are not glazed on the inside. I will see the difference, it will be interesting for sure.

[Karsty]

Regarding the point about yacht varnish.

One pot I have painted till smells of solvent after a week. My experience with solvents is they kill plant tissue outright. So I am going to put these pots in the oven for couple of hours. I guess about 50-60°C should do the job.

[adetheproducer]

Yeah get the varnish nice and dry a lower temperature would be better if your oven goes lower you don't want the varnish to crack.

[Karsty]

I painted the inside of a few more clay pots with yacht varnish, and even after leaving them in hot sun in a sun-trap with air movement for a few days, they still smell of solvent.

I've also discovered that yes, not all unglazed clay pots are porous. It seems that old Sankey Bulwell clay pots are not porous. I took a Cleistocactus out of one the other day, and realised that the roots had barely stuck to the sides of the pot. Also, when these pots are watered, the do not become damp on the outside. Modern small clay pots like Apta become obviously damp on the outside when watered, so it begs the question, do high-fired non-porous clay pots cause problems?