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  • Experiment: Rooting in Expanded Shale

    Not sure if expanded shale is readily available outside of Texas, but we do have it in nurseries and mulch yards. I use expanded shale as an alternative to perilte/vermiculite in my potting mix and raised bed mixes. It is great in that it breaks up soil and retains some moisture but does not break easily and it lasts forever.

    I am a big fan of rooting in DE, a method introduced by ginamcd. Pretty much all my rooting now is done in DE but i did find some pain points:
    • DE is very dusty and dangerous and must be washed due to silicate dust
    • I have to sift DE to only use large DE particles
    • DE can suck the life out of roots if left to dry out
    • The bottom of the DE in your cup can retain water and be pretty wet so there is potential for rot
    So i thought, let me try expanded shale as an experiment, i don't need to wash it, no sifting as they are all uniform in size, does not breakup and it can absorb water (10% - 30%) of its weight according to this study:


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    Now for my experiment, i wanted to verify the paper results and dried out my expanded shale in the oven, then soaked the shale in water for a few minutes. It ended up absorbing 10% of the water! According to the paper, if i leave it in water for 3-4 days, i can achieve 30% absorption. But for this first phase of the experiment, i am doing 10%.

    I tested this with a thicker mbvs cutting and a skinnier smith cutting, it took 1 month to show roots (without any clonex), similar to how DE performs without rooting gel.

    Here is expanded shale dry, wet, then with a cutting. I am using 24oz cup in a 24oz cup. I use glad press-and-seal to cover the top from drying.

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    MBVS after 1 month, 3 weeks

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    Smith after 1 month 3 weeks

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    Smith upshot, nice callousing:

    Click image for larger version  Name:	IMG-8974.JPG Views:	0 Size:	1.45 MB ID:	693357

    Some takeaways and notes:
    1. I thought this would fail due to the large size of the shale and not much water retention but those roots found a way through!
    2. Even though i did scrap the sides of the cutting, the roots only came out from the terminal end.
    3. Rooting was successful with 10% hydration
    4. I only did water every 2 weeks to re-hyrdate.
    5. Once roots showed, i gave it a light fertilizer solution.
    6. I up potted 3 weeks after roots
    7. Removing the expanded shale for up potting was easy, it doesn't matter if its wet or dry, but i did shear a little of the root.
    8. Very little expanded shale stuck to the roots and was easy to take off.
    9. I usually throw away DE after use as it breaks up quickly but will keep expanded shale to throw into my raised beds for better aeration

    Whats next
    1. Will report how up potting went for the mbvs and smith
    2. Testing with a cutting using clonex
    3. Testing with 20% - 30% hydrated expanded shale
    Hope someone can join the experiment!

    I know BrandonP is in texas and loves to experiment?
    Najam from Sugar Land, Texas, Zone 9a

    Wishlist: sao miguel roxo (azores dark), burgan unk, world's best mulberry

  • #2
    I've been meaning to try this DE method with Alifor. Tiny clay balls often used in orchid mixes. Thanks for posting, keep it up.
    Volcano, 7a VA


    • #3
      Interesting. Thanks for sharing. I don't have any expanded shale (yet at least), but I am looking forward to doing a few other tests this spring (particularly if some of my friends will let me cut limbs off their large Celeste and unknown fig trees for access to plenty of cuttings).

      One thing I wonder about is a possible role of biochar. This would be readily available to anyone who can burn wood, it would be safe and when finished with it can be thrown into a raised bed as a soil amendment (or just stick it back in your fireplace and use as charcoal). Could it be used alone for rooting, could it be added to another entity (perlite, shale, DE)? Last year I used it as an amendment in some of my seed starting mixes and mixed some in my garden.

      I've saved some from my fireplace and am just waiting for temps to warm up or more space in my house to try it with cuttings in some way. I need to see how much water it can hold as well.
      Last edited by BrandonP; 01-15-2020, 02:51 PM.
      Zone 8b, College Station, TX
      Wish List: Maltese Beauty, CLBC.


      • LLS
        LLS commented
        Editing a comment
        Biochar has a really high pH (like over 13) that will lock out nutrients from your plants. Most of the experiments I've seen with biochar have worse results as the percentage in the mixture goes over 50%. If you mix it with something acidic like peat moss, the pH will be more neutral.

        The roots might start in it, but the plant will not be able to get any new nutrients until it is up-potted into a better pH mix.

      • Noah Mercy
        Noah Mercy commented
        Editing a comment
        Agreed, ash from hardwoods is a major source of lye (sodium hydroxide, i.e. Draino). Should be a good source of minerals (and heavy metals, depending on input) but those are needed in trace amounts. Unburned cellulose becomes a nitrogen sink as it decays also. I think it would be good in a mulch, given time.

      • Dtownfigs
        Dtownfigs commented
        Editing a comment
        Be careful when adding nuggets of charcoal from your fireplace that came from un burned firewood. Biochar is created by burning in conditions that lack oxygen so you need to create special conditions for this to happen. Also consider charging it with a nitrogen source so it doesn’t pull nitrogen from the soil. Consider adding less than 10% to any soil

    • #4
      I experimented with hydroton, which I expect is very similar to alifor, but didn't care for it for rooting fig cuttings. Its good as part of an orchid mix though.
      Tony; Pickens county, SC zone 7b
      WL: Brooklyn White; Dominick; Golden Riverside; Maltese Beauty; Norland


      • Yoyo27983
        Yoyo27983 commented
        Editing a comment
        I have got one in hydroton right now, been in there since the 4th.

    • #5
      SO is this expanded shale available as a bagged commercial product available in commerce, r only in bulk from some TX producer locally?

      Here have minimal prob with optisorb de dust/fine particles. just male hole in bar top stand bag up stick hose inside down to bottom, turn on water and come back in an hour with all fine stuff washed up and out the hole around the hose. everything left is large enough to go straight into my tall rooting bags.

      Here secret seems not using 8 inch tall cups but 14 inch bags so wetter bottom DE is far from bottom of cutting that goes down only 5 inches. Bags have good bottom drain holes or are actually organza bags so can be watered even daily with no rot.Here the DE is cheapest and fortunately best indoor rooting medium,for me. I still prefer outdoor spring rooting in friable garden soil but like having candy in the cupboard, JUST CANNOT WAIT!



      • #6
        A large producer of expanded shale; multiple production facilities infer multistate availability.

        The huge rust colored horizontal furnace pipe must get really hot.

        Zone 9b
        S of Tampa Bay, FL


        • jessup42
          jessup42 commented
          Editing a comment
          Lightweight aggregate. Crazy! Id use it for backfill in large excavations if its suitable. In nj you could truck 30 tons no prob (i regularlysaw guys loaded with 35-40 tons recklessly). In nc law restricts loads over like 16 tons in tandem dump truck. Crazy difference makes material like this useful. Too bad not offered here

      • #7
        Excellent post - thanks for the photos also!

        South Arkansas - Zone 7b/8a - have Brown Turkey + 1 black madeira.


        • #8
          Great use of local materials! Id prefer this over DE anyday - my lungs hate that stuff. Your fatty boombatty roots look good for transplant with better success taboot! Well done. Awesome use of their hydration schedule for your experiment as well. Curious where the bell curve will see best results before dropping off - guess you'll see if 10% hydration is the sweet spot or if more/less hydration gets better results
          WNC zone 7a at the intersection of Mt Pisgah & the Blue Ridge Parkway