Snoofer's illustrated rockwool cloning technique

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Contributed by: snoofer

Submitted: 02-28-2003
Images archived 2003

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Successful cloning requires cleanliness, warmth, healthy stock, and a little TLC. Clones are sensitive to their environment; harsh conditions (ie. cold & damp) will delay rooting and increase mortality.

Why Rockwool?
Rockwool is an excellent medium for cloning: sterile, cheap, biodegradable, and portable, rockwool can be transplanted into any system with minimum transplant shock.

How many clones should I cut?
There will always be natural differences between clones; sheer numbers will compensate for poor performers and mortality. The fastest rooting clones have the most vigorous vegetative growth and usually the best flowering potential. I suggest taking 50% more than you need.

  • Rooting gel
  • Fresh razor blade(s) / quality trimming scissors
  • Cutting board
  • 1" rockwool cubes
  • Slotted tray / solid tray / High hat humidity domes
  • SuperThrive (@ 1 drop/gal)
  • No Damp (@ 5ml/gal in a spray bottle)
  • Flourescent lighting

  • Heating mat (40w GroTek mat on a cycle timer)
  • Isopropyl alcohol
  • Tray inserts: (I used Grodan 77 inserts - 55 clones/tray) keep cubes upright, evenly spaced, and slightly raised off the slotted tray.

    Note: always use "high quality water" when watering clones - distilled, reverse-osmosis (R.O.) or 24 hour tap water left for 24 hours to dissipate chlorine. All water should be at room temperature.

    Prepping the mothers
    The moms should be healthy, pest/disease free and fully into vegetative growth. Clones can be taken off moms up to 2 weeks into flower; however, these flowered clones experience shock and are often difficult to root.

    I like to foliar feed the mothers with Growth Plus (A Nitrozyme kelp extract containing growth hormones and vitamins) 3-4 days prior to cloning to encourage lush and healthy shoot growth.

    It is recommeneded to reduce the amount/ratio of Nitrogen in the mother's nutrient solution 3 days prior to cloning (flush soil mothers with water). Nitrogen inhibits root growth; reduced N levels in the mother should help the clones root faster.

    Some growers do not like to top their moms, preferring to take clones from lower shoots to maintain vertical growth. Lower shoots contain more stored starches, giving the clone more stored enemergy. Top shoots contain higher levels of growth hormones (ie. auxins) for faster root development.

    Prepping the rockwool
  • Remove plastic wrapping from cubes (The plastic can incubate algae)
  • Prepare some pH 4.5 - 5.5 water + SuperThrive (1 drop/gal)
  • Immerse cubes for 24hrs.

    I use plastic "Grodan77" inserts (11 cubes per insert, 5 inserts/tray for 55 clones/tray); keep cubes upright, evenly spaced, and slightly raised.

    I find the standard 1" cube too big; it remains damp and cool (even on a heating mat). I prefer to cut the 1" cube into 2 halves; the sized cube dries out faster, stays warm, air can reach all sides, roots exit faster, and you get twice as many! Cutting a cube into 4 makes even more...

    Labeling your clones
    Labeling your mom and the clones taken from a particular mom is a good idea to backtrack on a monster mom.

    Prior to cloning
    Exposed clones will wilt within a few minutes, so it is best to have all materials ready before you start to take cuttings.

  • Dip scissors and razor blade into alcohol (Grease is used to separate razor blades). Wipe cutting board with alcohol.
  • Drain cubes, place into tray.
  • Poke a 1/8" hole halfway into the center of each cube
  • Cover prepped cubes with dome until you are ready to start (I like to pre-warm the rockwool by putting the filled tray on the heating mat for hour before I start to take cuttings).

    Clone types
    Actively growing tops are preferred, as they contain the most growth hormones. Clones taken lower down are often spindly and less developed. I prefer 3" top clones with a 1/8" stem, 2-3 fan leaves and a slightly firm (but not yet woody) stem.

    I prefer short clones (no more than 2-3 nodes), otherwise the newly forming roots must support a large leaf and shoot. The clone should also be 'mature',with alternating leaves. Immature clones have leaves opposite each other and are usually pale and spindly.

    Avoid stem cuts (no node) and plug cuts, as they do not root nearly as well (Roots form primarily at the nodes). Trim large fan leaves in half to minimize the leaf area the newly forming roots must support.

    Selecting the clone (Where do I cut?)
    Select a vigorous growing top on the mother, cut the main stem just above a fan leaf / auxiliary shoot node about 2 nodes down (as shown in red in the image). The cut can be done with trimming scissors or razor blade.

    (Leaving a shoot and fan leaf on the mother allows the remaining shoot to continue growing and another shoot to grow from that node.)

    Pre-Trim the raw clone: (Removing lower nodes)
    Once the growing top has been selected and cut from the mother, trim shoots and fan leaves from the lowest nodes (as seen in the image). The lowest node will be inserted into the rockwool.

    Cut " below the lowest node with the razor blade at a 45 degree angle on the cutting board for a clean cut.

    The trimmed clone:
    This 'ideal' trimmed clone was taken from a vigorous top. A fan leaf and shoot were both removed at the lowest node. The clone will soon be inserted dipped into gel, then inserted into a rockwool cube.

    Trim large fan leaves in half (Reduces transpiration; the newly forming roots don't have to initially support as much leaf).

    Plant the clone

  • Dip the trimmed clone into the cloning gel, make sure the lowest node is also thinly coated with gel. Remove any excess on the cut surface itself (So the cutting does not suffocate).

  • Gently push the stem into the rockwool. If the hole is too big, gently squeeze the rockwool around the stem to seal it.

    Humidity dome and beyond
  • Spray inside of humidity dome with No-Damp solution (Do not spray clones directly, as this can encourage powdery mildew).

  • Rotate edge clones to keep their leaves inside of the tray. Cover the freshly cut clones with the dome.

  • Put the clone tray + dome under "warm white" fluorescent lights (Unrooted clones require low light levels. Do not blast them with direct HID lights!).

    The humidity dome should be left on for 2 days, lifted daily for air exchange. On the 3th day I like to prop up the dome " (slightly) on one side to acclimatize them (If wilting occurs, leave dome on for another day and try again). On the 4th day I remove the dome. Roots should begin to exit the cube 5-10 days.

    Daily Maintenance
    1. Air exchange
    Lift the dome at least once/day (for first 3-4 days, then remove dome). Breathe inside the dome to increase Co2 levels.

    2. Watering
    I water every second day when the clones are under the dome, then once/day thereafter. Once roots show, you may have to water twice a day to keep the roots moist.

    The pH of the water inside of the rockwool will rise slowly; re-hydrating @ 5.6-5.8 will restore proper pH levels inside the root zone. Allowing the cubes to dry slightly will force roots to search for water and encourage vigorous rooting (But dont allow the cubes to completely dry out!)

  • Mix 5.6-5.8 pH "24 hour" water and fill solid tray about halfway with water.
    Note: After the dome has been removed, add small amounts of nutrients -Micro + Bloom + 1drop/gal SuperThrive.
  • Dip clones + inserts + slotted tray into the filled solid tray. Make sure all clones are getting water by 'swirling' the edges of the tray.
  • Lift clone tray out and allow to drain. Shake tray to remove excess moisture.
  • Place clones back under fluorescent lights, and a gentle fan.

    Root check
    Roots should begin to exit the cube in 5-10 days. A gentle upward tug on the clone will tell you if it is rooted (only do this after 5 days). Unrooted clones will pull out. Roots may be present, but not yet exiting the cube. If in doubt, carefully open the cube.

    Clones will draw their nutrient needs internally from it's fan leaves, which may turn slightly pale. This is a good sign, as it is proof the clone is actively growing. Adding weak nutrients is recommended at this point. Unrooted clones often appear healthy and green (and will stay that way for weeks!).

    I prefer to sort out the clones (unrooted, few roots, vigorous) into their own trays. Roots should be white and fuzzy. If a clone has not shown roots in 2 weeks, I'd consider removing it. Brown roots indicate rot. Occassionally, root tips will become air burned: a sign to water more often!

    Weak nutrients (50-200ppm) should be started on the rooted clones, and watered more frequently to avoid drying the exposed root tips out. You could also try a weak foiliar feeding with Growth Plus (or any kelp extract). Begin to increase Nitrogen levels.

    Once the clones have fully established roots, they can be put under weak HID light and a weak (250-500ppm) nutrient regime, or outplanted into soil, hydro or aero systems.


  • Do not put the clone tray directly onto a heating mat. The heat will cook the roots, even on a timer. It is better to raise the tray off the mat. I use 2 coroplast strips to sit the tray on, raising the tray approx. ".

    A low-level continuous heat is preferred, but a timer may be required to reduce temperatures. I run my mats 5 min on, 10 min off, 24/7 on a cycle timer. The heat will dry out the clones quickly, and daily watering will be required.

  • Occasionally, fresh cloning gel will be very thick. Add some water to container, shake. The gel should pour easier. Some cloning gels have no fungicide (ex. Rootmax); fungicides inhibit root growth somewhat, but prevent damping off.

  • If you are using rooting powder, take care to remove excess powder from the stem cut as you plant the cutting, as this can inhibit the uptake of water.

  • Give your rooted clones a foliar feeding with Growth Plus (or any Kelp extract) to give them a quick growth boost once they have shown roots.

  • Don't forget to ventilate the cloning space

  • Cut many tops at once to speed up the cloning process.

  • Mark and date all trays, so you know when to expect roots. Try to keep different strains organized in their own trays, watered seperately.
  •   Last modified: 18:05 - Sep 27, 2002  

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