The Pro-Mix Days May Be Over, Where We’re At With Potting Soil Today

Well, we figured this day was eventually coming. The writing has been on the wall for a couple years now. But, it looks like our beloved Pro-Mix is pretty much unobtanium anymore in some parts of Alaska.

Sure, we probably could have hunted every store, nursery and gardening outlet and maybe we would have found it. But, that’s an unreasonable amount of effort, even for us. The price of Pro-Mix has been exceptionally high the last few years (almost $70 for 3.8 cubic feet), so I think retailers and customers have been getting a lot more price sensitive about something as basic as soil.

Plus, we are kind of here to do “representative” growing with you all. The more we diverge our practices from what “normal” people would do, the less relavent our techniques and efforts are to all of you.

We have been burned by many soils in the past, inducing disease, fungus and unexpected growth that were clearly brought in by the soils we used. That’s why we were so fiercely loyal to Pro-Mix, we just didn’t ever have those problems with it. We’re hopeful that this “mass marketed” soil that is so widely sold and used will be at least somewhat decent. Time will tell, though.

So, let’s talk about what we did get for potting soil this year! We opted for SunGro’s high porosity mix, which you’ll find at pretty much any “big box store” in your area. We chose high porosity version as it should be nice and airy for both a seedling mix, but also will be substantial enough for raising our plants. These mixes promote good soil drainage, so you don’t get a lot of water build up which can cause problems like dampening off. Plus, it’s fairly price friendly at nearly half the cost of Pro-Mix these days.

We’ll likely give you all a follow up opinion on this stuff, probably sometime in April. We’re going to run it through its paces, from germination to raising plants. We’ll know if it’s up to snuff by then and hopefully we have good things to report! Unfortunately, this may be late to the party for many of you. But, if you’re struggling with finding Pro-Mix this year, just know it’s not just you!

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8 comments… add one
  • Deborah Mar 17, 2024 @ 15:43

    Appreciate this post as I have been researching potting soil. The Lowes here does have the Sunshine Mix#4 for $35 for 3 cu ft. Bag. Does it really expand to 6 cubic feet? I never used a pro-mix before so I’m going to give a try. I also saw some reviews on Amazon for the gro-bucket insert that said the soil stays really wet so sure to use a well draining soil. Has this been your experience?

    I am going to look for the pro-mix you are going to try this year. I haven’t found that one around here. I’ll be interested to hear your experience.
    Also curious – you have another post on how you reuse your potting soil from year to year – so are you buying this soil you are speaking of in your post for seed starting and adding some to your soil compost pile? Wondering if you reuse, why you are buying more.


    • Jeff Mar 17, 2024 @ 19:52

      I think the “expands to 6 cubic feet” is a bit of a marketing gimmick. If you loosely pack the soil, sure, it’d likely take up 6 cubic feet. But, we try to make sure our containers are well packed as that’s beneficial for plants. I will tell you that ProMix is the best soil we’ve ever used and we’d still use it, if we could buy it locally. (Even if it’s $70 for 3 cubic feet!)

      And yes, well draining soil is important for GroBuckets. (So lots of perlite, usually, but can also be sand, vermiculite and other materials.) We build our own soil for our GroBuckets, but it’s very similar to a heavy perlite soil mix.

      We do buy new soil every year for germination and transplanting. Our soil pile is 100% frozen at this time, so it’s the only option. (It doesn’t thaw until late May/early June) But, we’d still do it even if it wasn’t frozen. Our soil re-use is primarily for our container gardens. In our germination and transplanting environment (indoors), we really don’t want a bunch of other seeds germinating, which happens with re-used soils. Everything we buy eventually ends up in our in-ground gardens or in our container soil, which eventually gets re-used.

      • Deborah Mar 19, 2024 @ 9:54

        Thanks for both of your replies! Maybe I missed it, but do you have a blog post on how you make/mix the soil for the grow buckets? Can you steer me in that direction, or tell me what you use inside the grow buckets? I’ve just purchased 30 buckets/inserts (and guide buckets) to give this a go this year and I am trying to get everything I’ll need in advance. Trying to figure out the soil needs now.

        • Jeff Mar 20, 2024 @ 0:58

          We do, yes! We do build all the soil we use in them, mostly due to cost. You can certainly use regular potting soil. But, at the point of using 30 buckets, you’re definitely in the territory where making your own will be slightly cheaper. We use the Frosty Garden Weapon soil, in this post.

  • Deborah Mar 17, 2024 @ 15:54

    Follow up – the Sunshine Mix#4 that I found here doesn’t say ‘high porosity’ – it says, With Mycorrhizae. Thoughts on whether this would be the right thing to use? Is the ‘high porosity’ important? The SunGrow you are trying is also ‘high porosity’ – so I’m wondering if that’s an important feature to have in the potting soil for the buckets?

    • Jeff Mar 17, 2024 @ 19:41

      As far as I know, these are different “versions” even though they both say “Mix #4.” That said, either should be OK and there’s not really a “right” thing to use. The high porosity is going to have more perlite in it, meaning it’ll drain water a bit better…but, the HP version also doesn’t have mycorrhizae according to SunGro. This is good stuff to get into your soil. (It helps with micro-soil structure, bacteria and otherwise creates a thriving biologic environment.) We’re less concerned about that since we use fertilizers that have it as well. We debated between the two and settled on the HP version as we like introducing perlite into our soils…but it’s not a mistake to use the other version, either.

      In the FWIW department, we are in the process of planning an update post in the next few days. We all ready know that we wouldn’t recommend the SunGro product for seed germination. Ours has all ready started to develop moss, we have soil-induced seeds germinating and worse yet, we’ve had our first fungal infection with it. We’re likely going to shift over to a DIY soil build for actual germination to get something a bit more sterile. There’s serious risks (especially from fungal infection) in the germination environment. But the SunGro stuff is fine for more established plants (i.e. post transplant) where they can resist these issues more easily.

      • Deborah Mar 19, 2024 @ 9:55

        Just to be clear, you didn’t have this problem using the #4 mix for starting seeds? Just this new mix you tried out?

        • Jeff Mar 20, 2024 @ 1:00

          We are having some problems with the SunGro #4 mix. Basically, we’ve determined it’s not good for germination. It’ll be fine for transplants, or even containers, with mature plants. Our most current post tonight summarizes our current thoughts with it.

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