PH of substrate and seed germination

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DaveW
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PH of substrate and seed germination

Post by DaveW »

Anybody know anything about the affect of soil PH on cactus seed germination?

I have just been asked the question what PH the soil should be by somebody sowing cactus seeds to get best germination. I cannot find anything on cacti, but I found this on the web which does indicate the PH of the substrate can affect germination:-

http://hortsci.ashspublications.org/con ... 2.full.pdf

I presume that cactus seed will germinate OK in the type of soils the plants are found occupying in habitat, though that may not be optimum. Seemingly N. American cacti will tolerate a slightly alkaline soil but seem to prefer a neutral one, whilst S. American cacti usually prefer a soil on the slightly acid side, but does this also apply for germination of their seed?
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ragamala
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Re: PH of substrate and seed germination

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iann
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Re: PH of substrate and seed germination

Post by iann »

I haven't had good results with cactus seed in alkaline soils, that is those with a small amount of limestone chippings that I would use for some adults. Hardly a double-blind study or even a statistical sample because I fairly quickly stop doing things that aren't working well. The few I tried were necessarily somewhat difficult species in the first place. Lithops don't seem to care and apparently germinate anywhere there is a bit of moisture.
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James Pickering
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Re: PH of substrate and seed germination

Post by James Pickering »

Good morning Dave.

I don’t post here often because my growing environment is so very different from yours. But, for what it is worth ..........

I have used so many soil mixes over the years. Recently I have used the following mix for seed germination and seedling/mature cactus growing:

80% Bach's Cactus Nursery mix plus 20% raw pumice (+/- ¼"/6.35mm).

Dan Bach's Cactus Nursery mix:
60% screened coarse and uniform (3/8"/9.53mm) horticultural pumice
20% high quality Canadian sphagnum peat moss
20% well composted shredded pine tree forest bark

The pH of this mix (slurry test using distilled water) is consistently 6.5 - 7.0

I have had excellent germination and seedling/cutting growing of the following species using this soil mix:

Arrojadoa dinae, multiflora, rhodantha
Micranthocereus polyanthus, densiflorus, streckeri
Discocactus horstii, buenekeri, crystallophilus, placentiformis
Melocactus matanzanus, bahiensis, catingicola
Coleocephalocereus aureus, purpureus
Uebelmannia pectinifera, buiningii
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DaveW
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Re: PH of substrate and seed germination

Post by DaveW »

Hi James,

Those look like species preferring composts on the acid side of neutral. Really I was asked if the PH of the compost affected initial germination rather than what they preferred to grow in once the initial root formed, but could find nothing on the web for cacti.

That's interesting Ian. Marlon Machado claimed cacti on alkaline soils only grew when they received acid rain and stopped when the rock turned the water alkaline. With seed however presumably that would mean they only germinated when they got acid rain and stopped growth as soon as things turned alkaline, meaning they only grew in short spurts unless initially the seed grew on some acid humus caught in cracks?

There seems to have been some work done on temperatures for cactus germination, but nothing on PH initiating it.
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Re: PH of substrate and seed germination

Post by RAYWOODBRIDGE »

Good point Dave, to be honest I don't know if or how it would effect germination , but just after germination I would think growth in slightly acid soil would be better than in a more alkaline soil,a paper by the American Society for Microbiology found more bacterial communities in Neutral and slightly acid soils than in soils that were at the two extremes of the Ph range, and that is usually better for plant growth.
The point you make re Marlon Machado is true in that South American cacti were known to show a spurt of growth after heavy thunder storms, the thunder rain was quite acid when tested, maybe those people who put vinegar into their watering can have got something after all.
To answer you original question I would say slightly acid if I had to make a choice.
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DaveW
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Re: PH of substrate and seed germination

Post by DaveW »

Thanks Ray and Ragamala,

Yes there is a lot of information on the Web as to the influence of heat and water on germination, but I could find nothing on the influence of PH on cactus seed germination. Logically most cactus germination in habitat is triggered by acid rain, so presumably the acid side of neutral is best for the compost and the water used to wet it.

I did find this interesting one on heat and water on germination.

https://www.sciencedirect.com/science/a ... 3016301967
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ragamala
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Re: PH of substrate and seed germination

Post by ragamala »

My thoughts on this are more questions than answers -
If germination in other plants tends to be better at around neutral or lower pH is there any reason to think cacti should be any different?
If rain triggers germination, is the washing away of germination inhibitors more important than the pH of the wash?
Is there anything to say categorically that some cacti thrive in or depend on alkaline conditions (rather than some developing a tolerance because of needs be)?
Is there evidence that soaking seed in low pH dilute acid produces better overall germination (rather than earlier germination)?

You mention "substrate", but my feeling is - as you suggest with reference to habitat rainfall - that germination is more likely to depend on pH in the water used for seed irrigation (or even surrounding top dressing wash-off) rather than the compost solution pH. It is possible that watering, ie soaking, seed pans from below may result in the seeds being subjected to different pH than direct overhead watering/spray.

Apart from the link I shared area this is the closest I came to specific research results -

https://books.google.co.uk/books?id=jdO ... ti&f=false

But the limited experiment result quoted focusses omore on shoot and root development than germination quality.

Buxbaum in his Cactus Culture book had theories about not germination but early seedling development, and seemed quite adamant that seedlings prefer conditions with lower pH, even if adult cacti "appear to be indifferent", and regarded alkalinity as lethal, including encouragement of algae. As a taxonomist he might not have had the scientific knowledge, but maybe we could do worse than follow his advice - after all what's important is not so much the days until germination, but the far longer period following when we hope a healthy seedling develops - so I go along with the general idea that neutral or slightly acid is best for seedling development and probably germination. And I'll continue using rainwater for both sowing and ongoing watering (I don't do baggies).
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Re: PH of substrate and seed germination

Post by Cactus Kid »

Hi Dave. There is some info on this in Franz Bauxbaum's 'Cactus culture based on biology' book.

If you don't already have it I could scan in and post / send you the relevant pages.
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Have a large balanced collection of both cacti and succulents but enjoy growing cristate, monstrose and generally anything a bit weird!
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DaveW
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Re: PH of substrate and seed germination

Post by DaveW »

Yes I do have Buxbaum's book thanks Cactus Kid. It deals with the seedlings rooting after germination though, not what effect the PH of the damp compost or subsequent watering's do on un-germinated seed.

Steve Thompson, one of our Nottingham Branch members, emailed me this information:-

"In Park S. Nobel’s book ‘Environmental Biology of Agaves and Cacti’ (written in 1988) on page 193 he says “A number of studies have examined the influence of pH on the germination of seeds of agaves and cacti.”

Unfortunately he only quotes research on agaves using hydroponic solutions - pH didn’t affect Agave deserti, in A. lechuguilla pH 7 halved germination compared with 6.5, and A. parryi germinated more slowly at higher pH. I think this indicates that around 6.5 would be good which matches the pH that is good for growth.

Nobel points out that experiments using hydroponic solutions can show the direct effects of various pH levels. But he says growth in soil is different because the pH of the soil affects the availability of nutrients because it affects how they bind to soil particles. So below pH 5, toxic elements are more soluble and nutrient elements are harder to absorb. Above pH 8.5 nutrients are in a form difficult for roots to absorb. (This would explain the different results in the Hort Science link (my earlier link DW) between germination on filter paper and in their peat and vermiculite mix)."
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