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Is sterilized soil necessary?

Posted by pjames 8/LA (My Page) on
Wed, Feb 24, 10 at 15:25

For the past few years I've used old potting soil mixed with some compost I make for starting my veggie seeds. I've used a combination of plastic cups with holes in the bottom for drainage to old 6 or 9 plant trays the stores sell their seedlings in. I sort of like the "do it yourself from what you have scrounged" approach.

I have read that sterilized soil is better or almost mandatory. This year I'm also looking to simplify things. I have read mixed reviews of the Jiffy starter kits but they seem economical. I'm thinking of using them and just throw my old potting soil and compost into the garden for the growing phase. Comments?


Follow-Up Postings:

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RE: Is sterilized soil necessary?

Well seed starting mix isn't actually "sterilized" as in autoclaved. It is just called "sterile" because the process used in making it and the heat involved tends to kill any pathogenic bacteria and the fungi that cause damp-off. So yes, using a so-called sterile seed starting mix is the standard recommendation.

That said, some swear by starting their seeds in compost or compost mixes. Problem there is it all depends on the quality of the compost and that varies greatly.

So while it may work for experienced composters and experienced seed growers it is potentially filled with problems and potential failures for the beginner or inexperienced.

While I can't personally recommend the Jiffy starter kits (if you mean the ones with the expanding pellets in them) as they have a whole other set of problems, plain old Jiffy Seed Starting Mix in any plastic container works fine and is cheap (and considered sterile). My preferred mix if you can get it is ProMix BX which is frequently discussed and recommended on many different forums here.

Hope this helps.

Dave


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RE: Is sterilized soil necessary?

One should sterilize potting soil before planting or transplanting the seeds or plants to ensure that they grow healthy and beautiful. The sterilization eliminates fungi, bacterial diseases and destructive bugs that may be in the soil.

So sterilization is good and mandatory upto some extent


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RE: Is sterilized soil necessary?

pjames, I would never, ever recommend the jiffy pellets. I also don't sterilize my seed germination mix. I rely on it to come already relatively pathogen free from the factory, where (as Dave says) it is steamed prior to bagging. I am careful about the storage of any left over product, and make sure to be a good housekeeper before, during, and after any horticultural procedures.


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RE: Is sterilized soil necessary?

Just my own observations... I started some seed in January & didn't sterilize the soil. It was my own mix of Peat, perilite & sand. I thought this would be relatively sterile, but I now have green mold growing on the top of this batch & my seedlings are struggling. I've tried to fix it with a fan/less water, but I've already lost over 50% of these. They were begonias & pretty delicate, I guess they just couldn't handle the stress.

I also started some a week later in the Jiffy seed starting mix, these seedlings are doing fine & no mold yet. Although I didn't sterilize the Jiffy mix, I plan to for all future batches. It's just too much of a risk for me to coddle these little guys, then lose them to that green sludge... I think in the long run it will save me time & I'll have more success.


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RE: Is sterilized soil necessary?

One should sterilize potting soil before planting or transplanting the seeds or plants to ensure that they grow healthy and beautiful. The sterilization eliminates fungi, bacterial diseases and destructive bugs that may be in the soil. So sterilization is good and mandatory upto some extent

Well for what it is worth professional growers NEVER sterilize their seed starting mix. So statements like the above just don't hold up to testing or scrutiny much less common practice.

In our greenhouse we have easily started well over 500,000 plants from seed over the years since we grow for sales and never once, in all those years, have we ever sterilized the mix. Ask any professional nursery or greenhouse grower if they sterilize their mix.

green mold growing on the top

Apologies but regardless of the mix used, green mold (which is really a type of fungus) is caused by excess watering and too warm growing temperatures. None of us think we are over-watering our seedlings but 99% of the time we are and the simple way to prove to yourself is just to force yourself to cut your watering in 1/2 and see what happens.

Molds, which are present in the air all around us will only grow under a very specific set of circumstances - wet, warm, enclosed stagnant air. So one can run their potting mix through a 1200 degree autoclave if they wish but as soon as the soil is exposed to the air the molds are back.

Dave


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RE: Is sterilized soil necessary?

Green mold is caused by soil that is too acidic. Wash and crumble some egg shells around your plants. Egg shell is mostly calcium carbonite. Calcium carbonite is the active ingredient in agricultural lime. It will sweeten the soil


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RE: Is sterilized soil necessary?

Thanks for the advice on the mold... I probably do have a tendancy to over-water & I started these on a heating mat, so the temperature was warmer in the beginning. I of course thought it must be the soil, but should have known it is more likely to be the human factor :) I plan to only use the Jiffy mix for the rest of my seeds since I'm sure it's more balanced, my own mixes are somewhat random...

Appreciate the tips!


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RE: Is sterilized soil necessary?

oilpainter- would Tums of the like (dissolved) work just as well (my tomatoes loved it last year)
Jiffy peat pods make me crazy due to the fine netting.
I am going crazy waiting for the first chance to direct sow;


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RE: Is sterilized soil necessary?

The calcium in egg shells ( calcium carbonate) is immobile and therefore useless to the plants until it is completely dissolved. I don't know about the Tums. Both solutions seem like a very expensive alternative to a bit of dolomite mixed into the soil or potting medium.

Green 'mold' is algae, which can be common on surfaces that are moist. If you see algae growing on a soil surface, it usually indicates poor drainage and/or excess moisture.


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RE: Is sterilized soil necessary?

I mix my own seed starting mix. I make the assumption that fungus and bacteria are everywhere and thus unavoidable. I concentrate on NOT providing the ideal conditions for their multiplication. It is only when starting seeds taking 30 days or longer to germinate that I ever have a fungus problem. This is solved with a spray of fungicide. Al


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RE: Is sterilized soil necessary?

I make the assumption that fungus and bacteria are everywhere and thus unavoidable. I concentrate on NOT providing the ideal conditions for their multiplication.

Well said Al!!

Dave


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RE: Is sterilized soil necessary?

I work in the operating room and am well aware of the omni-presence of fungi and bacteria. I guess my question was poorly worded in that 'sanitized' would be a more accurate term for commercially sold soils that are steam treated then dried to kill weed seeds and reduce bacteria counts.

My original question was whether to use a relatively 'inert' media like the Jiffy pellets (which I have decided against), store bought mix or my home-made compost.

I have decided to use my own compost which I treated by pouring some boiling water to kill off (hopefully) some of the remaining weeds seeds that are also ever-present.

I realize the nutrient level of the compost may be a little too high for good seed starting but I guess that is another issue for discussion.

I am stuffing cut paper tubes (toilet and paper towel) and will start some seeds this weekend in covered tubs I scrounged from the OR.


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RE: Is sterilized soil necessary?

I have some thoughts on this so I'll throw in my two cents.
I used to work in a plant genetics lab and we started seeds all the time. We started out by autoclaving our potting soil diligently. We didn't do it a couple of times and realised that it wasn't necessary, our plants grew just fine with very high germination rates.
Another thing, I doubt that common forms of algae/green stuff is that harmful to the plants. Fungus is another matter and sometimes insects can be an issue. Fungus is pretty hard to avoid but I would just keep your bags of potting medium tightly closed with as little air as possible when you're not using them and only scoop into them with something that is clean or pour out of them and close them tightly again.

It is a great point that if you are getting algae you are probably watering too much or it's too moist in your setup.

I just started a bunch of seedlings in peat pots using bags of peat moss, perlite and vermiculite. The first two are new bags so I'm assuming they're pretty clean but the vermiculite is something we have had for a while to furnish our spider tanks, I've kept the bag sealed so I'm hoping for the best.

Plants really want to grow, they are sessile so have always had to put up with whatever conditions they landed in, give them lots of light (natural and artificial) let them dry up when they're wet and let 300 and some odd million years of evolution take it's course.


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RE: Is sterilized soil necessary?

I think sterilization is necessary if you dig your own soil out of the ground. I'm with dig_dirt I, and more importantly, the plants love ProMix-BX. You can still make your own blend by adding compost or amendments.


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RE: Is sterilized soil necessary?

If your compost/old potting soil thing has been working for you, and you're continuing to sow the same kinds of seeds you've successfully sown in the past, it's probably fine. "Potting soil" can be so many things--I don't know what you're using. I've bought good stuff in the past, and I've also bought stuff that seems to be 50% sawdust or some such thing, and that doesn't do young plants any favors at all. Compost does have the risk of weed seeds, I suppose. If you know what's supposed to be coming up in your flat, that might not be a huge concern.

I do generally use fresh seed-starting mix that I either make myself (usually peat and perlite--and vermiculite if I have it) or buy (preference for Pro-Mix), but not always. And for tomatoes and tough things like that, I think a bit of compost can be beneficial. Sometimes I re-use my old stuff, and I don't sterilize. I won't re-use it if it was wet for a long time, has a green crust or smells funky. My rules of thumb are that I only re-use mix for things that I know are easy to grow and are sturdy as seedlings. Most vegetables fall into that category. Things that come up looking fragile or are as slender as hair I make sure to use a finer mix that's fresh.

And I'm in the peat-pellet haters' camp. I tend to underwater at times, and those things dry up on me seemingly in an instant. But they are fun to expand--sort of like Jiffy Pop.


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RE: Is sterilized soil necessary?

If you do use your own soil mix - to sterilize it - put into a metal roasting pan (-: and bake at 180F for 3 hours. Let cool and use!! I generally moistened mine to start with - seemed to help with the sterilization - steaming, etc


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