British Columbia: Wanted - Suggested Soil Mixes for Outdoor Pots in the PNW

Discussion in 'Outdoor Gardening in the Pacific Northwest' started by dt-van, Sep 17, 2020.

  1. dt-van

    dt-van Active Member 10 Years

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    Vancouver, Canada
    I have a number of large pots and window boxes which are potted up year round - bulbs in fall through spring and annuals in the summer with a few perennials like Heuchera and Primula for continuity. I find that all the commercially available "container" or "planter box"mixes consist of mainly peat moss and perlite - a light weight mix with high water retention to reduce the need for summer watering. Unfortunately in our wet winters with their regular freeze and thaw cycles these same mixes stay too wet and encourage bulbs and other sensitive plants to rot.
    I remove my saucers in winter and elevate the pots slightly to encourage draining, but wonder if there is a more suitable year round mix for our area? In one large planter I tried using a homemade mix with lots of bark fines, but the plants did not seem to do well at all. I replaced the soil with a container blend plus some "SeaSoil" and manure, but it still seems too wet in the Oct to March period.
    Does anyone have suggestions for a good commercial or homemade mix with better drainage for the wet season, but adequate moisture retention in summer?
    We used to put a layer of coarser material in the bottom, 'for better drainage' but some years ago I read on this forum that this actually creates worse drainage than a homogeneous mix. Apparently (because of surface tension?) the water stays in the wet soil and doesn't actually drain through the coarser material to the drainage holes. This explanation seems rather unlikely, but I'd like to hear more of other peoples experiences.
  2. Acerholic

    Acerholic Paragon of Plants Forums Moderator VCBF Cherry Scout Maple Society

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    Hampshire England Zone 8b UK
    @dt-van good afternoon, tbh it is very difficult to have the best of both worlds IMO.
    But here is my potting mix for young maples. John Innes no2 or no 3 for older trees, (this is basically a good quality compost). I then mix this with Horicutural potting bark, Horticultural grit, peat and a little perlite. It is a very loose mix and almost an alpine mix tbh. I add extra drainage holes to my pots and in the Winter and early Spring they are kept in a covered area.
    I am one of the people who do put broken crocks over the drainage holes to stop the soil from leaching out. (It works for me).
    You are doing the right thing by lifting your pots in Winter and removing the saucers, but do consider keeping this going throughout the Spring as well.
    I have found more problems for potted plants and trees through a wet Spring than at any other time.
    Hope this helps a little and my final say is 'Mix yourself for better results'.
  3. Georgia Strait

    Georgia Strait Generous Contributor

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    South Okanagan & Greater Vancouver, BC Canada
    I will re- read your excellent question again later as well

    I have two immediate thoughts - in addition to what I detailed about experience growing vegetables in large containers recently in this forum.

    1. I NEVER buy the mix that contains those odd gel water retaining pellets (I have in the past and I do not have success. I can see how it might work for hanging basket on hot dry side of balcony — then you toss the entire basket in October. I think that’s an unwise use of landfill (my opinion)

    2. BIG container w shallow soil ... I envision how these two plants you cite (above) live in a proper bed (or heuchera lives on thé rocks at Smuggler Cove Prov Park for example)

    And I try to copy that natural root area in a pot.

    And - I like the look and lift of large focal point pots - but not the soggy soil.

    Therefore I have put upturned smaller black Pots in bottom of large containers - then some good Sea Soil brand for containers

    A lot of what I have is old bagged soil dumped out of old pots — that has been mixed and mingled over time — it ends up in a large bin (normally sold for garbage) that has a lid and drain hole ... and the bugs are happy to chew it up and I use it for ornamental plants. Not scientific at all - kind of like common sense cooking!

    I understand you may seek an instant solution for a limited size space. Let us know if that is the case - like condo balcony or townhouse 10x10 patio idea.

    OR - if you have a large lot or acreage - then more options for this question

    Feeding and watering is a big part of potted plant husbandry — in a short answer - i would say less is more and pay attn to plants and follow their natural cycle for this climate and part of the planet.

    ÉDIT to add — your sun and climate exposure incl wind makes a diff too — and obviously your plant choices - I am now at stage where I realize the hundreds spent in certain plants will not make them grow. So I have old containers of hosta and seasonal coleus and fern and other shade tho dry plants and then amp them up w a couple of splurge $ annual Colors if budget and time allows
    Last edited: Sep 17, 2020

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