Pot soil

Discussion in 'Outdoor Gardening in the Pacific Northwest' started by soccerdad, Jul 25, 2022.

  1. soccerdad

    soccerdad Active Member 10 Years

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    I am going to be using some very large pots. What should I fill them with? The answer, if I look at the bags in
    the stores, is some sort of special container mix. But why?

    Fill a huge cylindrical pot with garden soil. set it on the middle of my garden, and put a plant in the middle. It will not be affected by the fact that it is in a pot. To anthropomorphize a bit, it won't even know it's in a pot. It will grow exactly as if it were planted in the soil that now lies beneath the pot.

    So why wouldn't I use garden soil in my pots?
     
  2. vitog

    vitog Rising Contributor 10 Years

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    One reason is that garden soil is typically much denser than potting soil, which shouldn't matter if you're never going to move the pot.
     
  3. Pieter

    Pieter Active Member 10 Years

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    Couple of things to keep in mind here. First of all, if your pots have their drainage hole(s) on the bottom the drainage will be impeded by the substrate you put it on, having the container elevated even only an inch will greatly help proper drainage. Secondly, water is your friend and water is your enemy. You have to make sure water is not allowed to sit in the root zone for days on end, that'll lead to root rot. Don't be tempted to put 'drainage material' in the bottom of the container, it will have the opposite effect of what you are trying to achieve, see Linda Chalker-Scott. In any container there is a so-called 'perched water table' you fight for aeration, see rocks in pots. If the roots see naught but water and no oxygen they wither and die. I do a lot of gardening in containers, varying in size from your typical 1-gallon nursery pot to the large ceramic planters to large draped-cement pots. They ALL have potting mixes in them, none have garden or top soil and the ones with large perennials in them have the pots emptied and the potting mix refreshed about every 3 years or so otherwise the plants don't get anywhere near their potential size. Refreshing the potting mix helps keep it loose and friable, after 3 or more years it collapses, reduces drainage and aeration and impacts the health of the root system and ultimately the plant.
     
    Last edited: Jul 31, 2022
    Keke likes this.
  4. Keke

    Keke Active Member 10 Years

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    Because I largely garden on a roof deck, all my pots are filled 1/3 with packing peanuts to save weight. To avoid perched water tables, I place a piece of soft (usually nylon) rope vertically in the pot before I fill it. One end goes out a drainage hole at the bottom (pots are on pot feet) and the other sits within a centimetre of the top of the potting mix. It breaks the perch by wicking excess water out the drainage hole. But I agree with Pieter, it's the "fluffiness" of the potting mix that allows longterm planting in pots. In the ground, earthworms and other small garden critters do the same thing, but even if you add them to a pot it doesn't work the same!
     

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