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Cacti & Succulents

Should I sterilize my cactus potting soil?

12 years ago

Hi everyone

I am going to pot a Prickly Pear pad in a few days and I was wondering if I needed to sterilize the soil first. I have some seedlings that I have been growing for about a year and a half and I remember sterilizing that soil before sowing after reading some how-to articles.

I also read some articles on Prickly Pear propagation but I didnt see anything on soil sterilization. I should also mention that my cactus soil has been stored in a cabinet in the garage for the past year. With all the dust and everything else flying around, I am wondering if the soil could have possibly been contaminated.

Thanks

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Comments (6)

cactusmcharris, interior BC Z4/5
12 years ago
That soil sterilization is particularly important for seed-growing, but with Opuntia pads I'd think you're OK with using it as is; Opuntia pads don't particularly like being pampered, like you might your other plants.
wilsocn
Original Author
12 years ago
Thanks for the help, charris. Straight into the soil it is then.
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I think the first question is going to be - what are you hoping to use it for? I ask because some mixes are pretty much 'sterile' already, and perform just fine. However, even though many people apply the term 'sterile' to planting mediums, it should be noted - just for accuracy's sake - that it's almost impossible to sterilize soil without extremely harsh chemicals, or equipment not available to the average person. The closest that the average person can come is sanitization, and to keep it that way is next to impossible. Many products used to create mixes are - barring contamination - pretty much 'sterile'. Vermiculite and perlite are examples. Another issue that your post addresses is this issue of mycorrhizae. Now, it's true that some plants can form symbiotic relationships of this type, and there's no doubt that fungi (as well as other soil life forms) do play an integral role in the cycles that affect plant growth in nature, but these relationships are not necessary at all. This is why I asked about what will be your use of the potting soil. If it's for container plants, don't sweat the issue. There's a lot of hype surrounding mycorrhizae because it's one of those new products for which companies are trying to establish a market. Plants have been growing in containers for millennia. No special products necessary. This isn't to say that some things help more than others, it's to say that spores are EVERYWHERE! Wait... you just breathed in a thousand of them lol. If you want to grow a tropical plant, for example, then odds are that any mycorrhizae that have a relationship with that plant will only thrive in the tropics. The products that are sold as mycorrhizae only contain a few species, and doubtfully those for tropical plants. So... 'sterilization' of soil is really only important for those people who don't want to introduce bugs or diseases. And if you haven't experienced these problems, it's not really an issue. If you are running a commercial operation, and you want a good reputation, then finding a 'sterile' (sanitized) mix may be more important to you.
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xerophyte NYC
12 years ago
I have never even attempted to sterilize anything - the second a sterile batch of soil is exposed to air it is introduced to numerous spores and airborne algae particles (if you are near the ocean), so I don't believe it makes a difference - seeds or otherwise. And you also wind up killing beneficial bacteria which outnumber the bad guys.

If sterility is a concern, just use an inorganic substrate.

x
penfold2
12 years ago
...if you are near the ocean...

And even if you are not. I can set up a saltwater aquarium here in MN, and it will quickly become populated by algae whose spores have been carried by air currents all the way from the Pacific Ocean. It's really amazing how much stuff is just floating around in the air.

I have to agree that any sterilization is only momentary. Good cultural methods will prevent inevitable pathogens from taking over. What little seed growing I've done has been with a gritty soil and substantial air circulation in order to prevent the wet, stagnant conditions that allow pathogens to thrive. And the Opuntia pads we're talking about here are mature growth that is much less susceptible to pathogens than seedlings.
ggarner
12 years ago
In our commercial operation we used to sterilize soil that we made, but this was not because of any air borne pathogens or fungii. It was due to the fact that we used a tractor to mix up 20 yards of mix at a time and the "bad" pathogens tended to come from ground contact (nematodes etc) We put the soil in carts and attached a 3" steam line we had going to a boiler and would steam the soil for about 90 min.

Ever since getting 2 mixers (1 is a rear end off a cement mixer, and the 2nd is a proper soil mixer) we have abandoned sterilization, because it is not needed. We have had no problems for the past 10 years running with 0 sterilization, even for propagation where you would see the most problems.
land3499
12 years ago
>If sterility is a concern, just use an inorganic substrate.

That won't make any difference!

Most prickly pears (opuntioids) will grow in just about anything from pure peat to air, so now worries.

-R

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