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PH + cacti

Discuss repotting, soil, lighting, fertilizing, watering, etc. in this category.

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PH + cacti

Postby teo » Thu Oct 14, 2010 5:56 pm

I understand that at least some cacti grow better in slighlty acidic soil. Is this true for all genera? Are there some that would benefit from pH > 7?
I have no practical choice than to use my ordinary tap water (which is somewhat hard in my area). Is it good to add an acid (such as vinegar)to the water to get a lower pH. Will this have other side-effects on the soil (fallout of salts?). I'm looking for advice in this area (I will search on the net).

What about other succulents?
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Postby Pilif » Thu Oct 14, 2010 9:24 pm

as a general rule of thumb:
cacti from north america like basic soil,
cacti from south america like acidic soil.

But this is just a general rule!
Every plant has different needs, you'll need to do some research. Gymnocalyciums for example (south american) will stop growing and loose their roots in basic soil.

I myself use vinegar to lower the ph of my tap water to 6-6.5 to water specific plants, while I use 'normal' tap water for the other plants. The best things to use are rain- and distilled water, but this isn't allways an option.
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Postby luddhus » Fri Oct 15, 2010 6:43 am

This is a topic of much debate. Briefly, some growers believe that plants do best in a growing medium that resembles the soil in habitat. Others claim that plants have the same kind of root cells and that they all like a pH of 5.5-6.0, but some have developed defence mechanisms that allow them to grow in a more hostile environment. There are people from both sides who swear that their observations support either of the two theories.

Maybe the whole thing is too complex to have a simple answer (too many other factors involved), and you might have to try both and find combinations of soil + water that works for your plants. Some species are more picky about soil etc. than others. Most of my plants are grown in slightly acidic conditions, but if a plant does not grow well, adding limestone is one thing that I might try (if it is a species that grow in alkaline soil in habitat).
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Postby iann » Sun Oct 17, 2010 10:37 pm

Regardless of your soil, using hard water longterm can cause problems. One of the most visible is the buildup of limestone deposits. You get them around the top of the pot, on the plant if you aren't careful, and out of sight they can clog up the soil. The deposits can be dissolved away using an acid but this is a slow process, perhaps best done by leaving the pot out in the rain for a few weeks (you'll goodness Britain sends all that acid rain!).

Hard water on an acid compost is a particularly bad combination. The acid soil, mainly the organic components, and the alkaline water will react and the result tends to be a nasty mess.

Hard water on an alkaline soil shouldn't cause any immediate problems, but may produce nutrient deficiencies. Certain nutrients are not available in alkaline conditions and one of the ways that plants get access to them is because slightly acid rainwater makes them available. There are other mechanisms involving acidic secretions from the roots and symbiosis with fungi and bacteria, but just remember nutrient deficiency of the plants start to look a big jaded. One nutrient that is always in short supply on alkaline soils is nitrogen, and limestone specialists are usually slow growing plants.
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Postby TimN » Mon Oct 18, 2010 5:53 am

Definitely get heavy crust with the very hard water here in PHX. It seems to be worse when I acidify the water.

There was a recent article in the CSSA journal about ph and uptake of nitrogen. Apparently it's difficult in alakaline conditions. Type or nitrogen provided is also important.

I'm trying to find a local source for potassium sulfate and ammonium sulfate which were recommended in the article.
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Postby luddhus » Mon Oct 18, 2010 8:27 am

TimN wrote:It seems to be worse when I acidify the water.


Worse? What kind of acid did you use?
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