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  • Salt for rooting humidity?

    Has anyone ever tried using salt to maintain the humidity in a rooting box?

    Salt has a great property where it will maintain the relative humidity inside a container to about 75%. Shouldn't that be a fairly ideal humidity to root cuttings in? Not too high to rot and not too low to dry the cuttings out.

    Should be as simple as adding a certain amount of salt (maybe 250g?) in a cup to a container and then seal your cuttings in that container for a few weeks.

    Ammonium sulphate would be an alternative to bring the humidity up to 80% but salt seems like such a cheap readily available ingredient.
    Don - OH Zone 6a Wish list: Verdolino, Black Celeste

  • #2
    That is an interesting idea, are you having a hard time keeping humidity? I live in an area with no humidity and have to keep my bin vented to keep the humidity down. That is with only barely moist perlite.
    Scott - Colorado Springs, CO - Zone 4/5 (Depending on the year) - Elevation 6266ft

    “Though the problems of the world are increasingly complex, the solutions remain embarrassingly simple.” – Bill Mollison


    • #3
      I was just trying to think of a fool proof, easy, hands off way to root cuttings. A set it and forget it type of recipe with high success rate.

      Sealing the container at the correct controlled humidity level seems like it would prevent having to futz with opening the container regularly to try to prevent mold and also keep critters like fungus gnats out.

      My initial thoughts would be to try to:
      Sanitize the cuttings and containers
      Pot them in barely moist sterile media
      Place the cups/pots and a cup with salt in the container
      Seal it up, store it around 70-75 F, and check back in a month to see what rooted
      And finally transition to light and normal humidity.

      Maybe even store in a clear container in shade to help with the light transition.
      Don - OH Zone 6a Wish list: Verdolino, Black Celeste


      • #4
        they have two way moisture control packs - http://www.bovedapacks.com/catalog.aspx?catid=1
        the packs are really cheap and work wonderfully. they have been used in the cigar industry for a while now.
        the issues with salt that concern me is that water will absorb the sodium, and then turn into vapor in the dome. Then will make contact with the plant surfaces, and as a result it could possibly coat the plant material and pull moisture away from the plant.

        one more thing to keep in mind is that if leaves come out while sealed; they could potentially start transpiring, and when they do they give off ethylene. which has the potential to cause a brown out. while in the greenhouse getting cuttings that were shipped, we had to remove them from boxes and open up the bags to prevent this.

        Just wanted to throw all this out there. For all I know it could work brilliantly!


        • #5
          Humidor packs look interesting. Thanks for the link.

          I don't know that I'd be worried about the salt evaporating with the water. I would think that all of it would be left behind if the water evaporated from the salt. Just like distilled water.

          I have no idea about the ethylene gas buildup.

          Maybe I'll have to try some tests.
          Don - OH Zone 6a Wish list: Verdolino, Black Celeste


          • #6
            I've never tried it.

            But the initial "high" humidity is only needed to hydrate the cuttings prior to actual rooting. To speed root production a separate "Pre-Hydration" step, pre-soaking the cuttings in dripping wet Sphanum Moss or Coir (low PH) for up to 3 days will reduce the initial rooting times. The humidity level is easily maintained by keeping the temperature between 70 deg F and 78 deg F and ensuring that the medium is moist / damp but not wet. Whether using a direct plant or (pre) rooting in bag I've not had to resort to any extreme methods to maintain humidity in the rooting stage.

            The attached photo is an example of 3 days pre-hydration and 17 days rooting with Coir in a 1 gallon ziplock plastic bag. No Rooting Hormone was used, the bag was only "inflated" every few days, they were placed in a dark closet with a temperature of ~ 70 deg F - 79 deg F.
            Click image for larger version

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            Last edited by AscPete; 05-22-2015, 11:45 PM. Reason: added photo and caption
            Pete R - Hudson Valley, NY - zone 5b