Asexual Reproduction-Cloning

The concept of creating an exact replica of a living being through cloning has been the topic of many si-fi and horror stories throughout the ages.  The thought usually conjures up some image of a Frankenstein like monster whose genetic structure has gone haywire during the cloning process. 

Cloning is the genetically identical duplication of an organism through asexual reproduction. Scientists have made some mind boggling achievements with cloning, including the asexual reproduction of sheep and cows.  There is much ethical debate as to how far and for what purpose cloning should be used. However cloning, or asexual propagation, has been common practice in the horticultural world for hundreds of years.

Simply taking a stem cutting from a 'parent or mother' plant, rooting and planting it to create a new plant is cloning or asexual propagation in it's most basic form.  From Frankenstein to Grandma's geraniums!

The greatest advantage of this form of propagation is that all the desirable traits of the mother plant will be reproduced in it's offspring. The strain, quality, smell and taste will be identical with every cutting taken. Chronologically the cuttings will be the same age as their parent plant and will produce flowers much earlier than their seed grown counterparts. Bad characteristics will also be inherited by the rooted cutting.  It is for this reason that particular care should be taken when selecting a mother plant.

A mother plant should be healthy, hearty, insect free and in its vegetative growth stage to produce strong cuttings.  Mother plants need plenty of nourishment and light so the cuttings will have reserves to ensure quick rooting and ultimately, survival.

Prepare the mother plant prior to taking cuttings.  Leaching will remove any excess nitrogen from the plant.  Nitrogen will cause the cuttings to concentrate on producing foliage rather than roots. Leach the day before taking cuttings by rinsing the root zone with straight pH balanced water. Reduce stress by foliar feeding the mother plant with a B₁ hormone three days prior to taking cuttings.  The mother plant will recover and be ready for another round of cuttings in about 6 weeks.

New growth on the mother plant will make the best cuttings. The young, tender shoots produce roots quickly and easily making them less vulnerable to fungus or disease.  The mother plant should be kept under 18 hours of light per day to enable it to maintain strength and retain all its desirable characteristics. 

Although cloning produces the identical traits of the mother plant, environmental conditions may vary greatly affecting the development of the cuttings.  Insufficient light or humidity or too high or low temperature will drastically alter the appearance and quality of a clone.     

There are several parts of the plant that can be rooted.  Leaves, stems, roots and growing tips have various requirements for propagation and rooting.  The most common method used is stem cuttings because it requires minimal equipment and results are rapid and consistent.  When rooting stem cuttings you can expect around a 90% success rate under ideal conditions.  There will always be some slow starters or unexplained wilting.  Remove these cuttings immediately as they may endanger the healthy ones.

All equipment and growing trays should be sterilized prior to use with a solution of 1 oz. liquid bleach per gallon of water. Cleanliness is essential and hands should be washed regularly during the cutting procedure or rubber gloves worn. 

A cutting should be approximately 3" in length.  Use a sterile, very sharp knife, razor blade or scalpel to sever the cutting from the mother plant.  Never use your fingernail or scissors as this will cause bruising and crush the tender tissue causing the cutting to rot.  Make the cut just below a node or leaf joint on a 45° angle to maximize the available rooting surface. Scraping the outside tissue off the bottom 2 inch of the stem with a razor blade or scalpel will add to the rooting surface. Ideally cuttings should be taken in a cool shady climate away from direct sun or strong artificial light to avoid drying and damaging the cut surface.

Carefully remove all but 3 or 4 of the top leaves from the cutting making sure not to strip the bark or stem skin with the leaf.  This will ensure that all the reserved energy in the cutting will go into the manufacturing of roots rather than into feeding extra vegetation. Any leaves that are submersed in the rooting media will rot causing the cutting to die.

Treating cuttings with rooting hormones will speed up root development and help establish a strong foundation. Some rooting compounds contain anti-fungal agents for extra protection.  Simply dip cutting into the powder, liquid or gel rooting hormone to thinly coat the surface of the cut end.  Allow excess to drip off or if using powder gently tap the base on the edge of the container. This should be done immediately after the cutting is severed to prevent air from getting trapped in the stem and to seal the cutting.  If taking multiple cuttings, immediately place each shoot in a container of water until they are ready to be treated with the rooting hormone.

Cuttings are now ready to be inserted into their rooting medium.  A sterile, well draining medium with good oxygen and water retention properties is ideal for cuttings. There are several growing media that work well; perlite, vermiculite, peat pots and oasis cubes, to name a few.  We will focus on the use of rockwool, a spun rock fiber that resembles insulation, as it possess these qualities and is inexpensive, lightweight, clean and easy to use.

Rockwool propagation slabs fit into a standard nursery tray and accommodate 98 cuttings.  Rockwool slabs must be pre-soaked for 12 hours and balanced to pH 5.0 - 5.5. prior to receiving cuttings.  Allow to drain well and place in a sterilized nursery flat. Rockwool flats must not stand in water in the trays.  Use a 2 part tray with holes and liner or line the bottom of a tray with heydite or clay pellets. Transfer the cutting directly from the rooting hormone to the rockwool.  Gently fit cutting stem securely into the prepunched hole in the rockwool slab keeping it about 1/2" off  the bottom.  Gently pack the rockwool around the stem making sure not to wipe off the rooting hormone.  The rockwool must be in direct contact with the stem to allow the cutting to absorb moisture. If no hole exists make one with a sterile instrument making sure the cutting fits firmly in place. 

Cuttings require high humidity during rooting.  As they lack roots, moisture can only be absorbed through the stem and leaves.  Humidity domes should be used to ensure that humidity is kept above 70%.  Misting the leaves once a day with a vitamin B₁ solution will help eliminate stress from transplanting and increase water uptake. Make sure the rockwool is kept moist.

Nutrients should not be given to cuttings until roots have been established. Feeding cuttings will promote vegetative growth rather than root development. Good root development is necessary for a high yield in the later stages.  Roots usually appear within 7 - 14 days.  Once roots are formed, introduce nutrients gradually starting at 1/4 strength or as recommended by the manufacturer.  Slowly increase to full strength, around 3 weeks.

C0₂ is essential to root development.  Remove the dome for 5 to 10 minutes daily.  Gently blow on the cuttings or wave the dome in a fan like motion over the cuttings to remove stale air and replace with fresh C0₂ rich air.

The ideal temperature for cuttings is 75° - 80° F.  Lower temperatures will slow rooting.  A thermostatically controlled heating mat designed to fit under a standard nursery tray is a convenient way to ensure cuttings will be kept warm which will drastically reduce rooting time.  Be careful not to let temperatures get too high.  This will invite fungus and a host of other potential problems.

Cuttings require 18 hours of light per day followed by an eight hour uninterrupted period of total darkness.  The dark period is when most of the root development will occur. Fluorescent or metal halide lighting are a good source of supplemental light for cuttings.  Be sure not to place cuttings too close to the light as this will cause tender shoots to burn. 

Once roots are present the cuttings are ready to be moved into a hydroponic garden. Use the same growing medium as the cuttings were rooted in whenever possible.  Rockwool propagation slabs can be broken off into 1" cubes and placed inside a 3"or 4" cube which will be their home through maturity. 

The transplanting process is probably the most stressful time in a plant's life. Transplant late in the day to provide recovery time from the stress during night.

Cloning, when done properly is a very efficient, inexpensive method of plant reproduction.  It offers the grower an opportunity to experiment with different environmental conditions, nutrients and growth additives without risking expensive store bought plant material.  Follow these simple guidelines and you should yield a 90% return on your cuttings. 

George Van Patten's book, Gardening Indoors with Cuttings is an excellent reference and walks you step-by-step through all the various methods of cloning, potential hazards and different growing media.

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