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ottawan_z5a

What is difference- Rooting in water & frequently watered perlite

ottawan_z5a
13 years ago

I had asked this question in other threads but it got buried with no traction. The question was if it was harmful to frequently water cuttings in perlite with good drain holes in the rooting pot, say at least once a day. I am not botany expert but I can imagine some benefits like inert moist environment in perlite (unlike soil where things can harm the bark in very moist situation) and fast return of air/oxygen after water run off from perlite through the drain holes. The cuttings may be in perlite from the start or after getting initials in the baggie method.

Now, recently there have been a few threads about rooting in water where the cutting always stays inside water to a certain height. Many have shown successful rooting & some unsuccessful with rotting bark.

I can practice myself with spare cuttings to see if frequent watering of cuttings in perlite with good drainage will have any detrimental effect but I thought to ask in case someone from experience or otherwise already may know that it is OK to water cuttings in perlite frequently say at least once a day (or may mention both positives as well as negatives of frequent watering in perlite).

Comments (2)

  • tapla (mid-Michigan, USDA z5b-6a)
    13 years ago
    last modified: 9 years ago

    You can start by reading something I wrote a while ago, then posing any questions you have:

    Though roots form readily and often seemingly more quickly on many plants propagated in water, the roots produced are quite different from those produced in a soil-like or highly aerated medium (perlite - screened Turface - calcined DE - seed starting mix, e.g.). Physiologically, you will find these roots to be much more brittle than normal roots due to a much higher percentage of aerenchyma (a tissue with a greater percentage of inter-cellular air spaces than normal parenchyma).

    Aerenchyma tissue is filled with airy compartments. It usually forms in already rooted plants as a result of highly selective cell death and dissolution in the root cortex in response to hypoxic conditions in the rhizosphere (root zone). There are 2 types of aerenchymous tissue. One type is formed by cell differentiation and subsequent collapse, and the other type is formed by cell separation without collapse ( as in water-rooted plants). In both cases, the long continuous air spaces allow diffusion of oxygen (and probably ethylene) from shoots to roots that would normally be unavailable to plants with roots growing in hypoxic media. In fresh cuttings placed in water, aerenchymous tissue forms due to the same hypoxic conditions w/o cell death & dissolution.

    Note too, that under hypoxic (airless - low O2 levels) conditions, ethylene is necessary for aerenchyma to form. This parallels the fact that low oxygen concentrations, as found in water rooting, generally stimulate trees (I'm a tree guy) and other plants to produce ethylene. For a long while it was believed that high levels of ethylene stimulate adventitious root formation, but lots of recent research proves the reverse to be true. Under hypoxic conditions, like submergence in water, ethylene actually slows down adventitious root formation and elongation.

    If you wish to eventually plant your rooted cuttings in soil, it is probably best not to root them in water because of the frequent difficulty in transplanting them to soil. The brittle "water-formed" roots often break during transplant & those that don't break are very poor at water absorption and often die. The effect is equivalent to beginning the cutting process over again with a cutting in which vitality has likely been reduced.

    If you do a side by side comparison of cuttings rooted in water & cuttings rooted in soil, the cuttings in soil will always (for an extremely high percentage of plants) have a leg up in development on those moved from water to a soil medium for the reasons outlined above.

    *****************************

    Some key issues in determining whether or not cuttings will strike are the state of health/vitality of the plant material the cuttings were taken from, whether or not there are disease organisms in the rooting medium (all unsterilized peat-based media does), how well-aerated the rooting medium is in relationship to how deep the cuttings are stuck.

    Al

  • ottawan_z5a
    Original Author
    13 years ago
    last modified: 9 years ago

    Thanks Al.
    My concern was mostly with existing root progress with frequent watering in perlite only medium and not with the initial speed of rooting.
    My idea was that in case of chunky material like perlite or turface (or its mix) when watered, the chunky material absorbs some moisture but the water gradually drains away and air/oxtgen return to spaces between the chunks so the roots get fresh air/oxygen and moisture. In case of perlite/turface there is moisture present but not wet like peat moss based medium. When perlite or turface is watered the next day again, water fills up the voids for a short period, removes the stale air but gradually the water drains away and fresh air/oxygen comes in. Thus there is a cycle of moisture (no continuous wetness) and fresh air/oxygen that I thought should be helpful for the roots.
    Now I have less concern with frequent watering in perlite-only after reading the threads about rooting in water-only and Al's comparison of roots structure in different media:

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