Propagation

 

Plant propagation is used to produce new plants from a desired parent plant. There are two categories of plant propagation:  asexual and sexual. Asexual propagation is used to maintain selections of known identity and quality and includes such techniques as division, air-layering, grafting and cuttings. Sexual propagation is a natural process resulting in a parent plant forming seeds that reproduce the plant but the offspring are not clonal as in asexual propagation. Both types of propagation have positive attributes.  Asexual propagation allows you to reproduce or clone the parent plant exactly.  This is especially useful when the parent plant has desirable characteristics such as brilliant flowers or superior fruit.  Asexual propagation preserves the characteristics of the parent plant.  The plants produced by asexual propagation will also flower and fruit faster than those produced by sexual propagation because plants grown from seed need to pass through a juvenile period before they flower and fruit.  Asexually propagated plants are mature when they are propagated and begin to flower immediately. Sexual propagation has several benefits as well. Growing from seed is cheap and easy.  Growing plants from seed produce offspring which are not genetically identical to the parent; therefore, the propagated plant will be genetically diverse from the parent plant which is a desired characteristic in a natural setting.  



TYPES OF ASEXUAL PROPAGATION



Division:  Division is among the simplest types of asexual propagation.  Division is suitable for plants such as bromeliads and orchids, as well as, grass relatives such as bananas, gingers, heliconias and bamboo.  These types of plants naturally multiply as they grow (bromeliads and orchids) or clump by sending out rhizomes (bananas, gingers, heliconias and bamboo).  The plantlets produced by the bromeliads or orchids can be carefully removed when they are approximately 1/3 the size of the parent plant.  These plantlets will grow into mature plants on their own if placed in well draining potting media and watered sufficiently.  Clumping plants grow from the center of the plant out, so the best place to get new plant material is on the perimeter of the plant.  When dividing a clumping plant, it is sometimes only necessary to get one or two rhizomes in order to make a new plant.  These rhizomes are then planted in a well draining potting media and watered sufficiently.  



What you need to know about plant structure:  Before the remaining types of asexual propagation are explained, you must learn a little about plant structure.  Cuttings, air-layers and grafting will not work with grass relatives such as palms or bamboo (monocots).  These types of asexual propagation work with plants classified as dicots.  It is the unique structure of dicots that allow these processes to work.  A dicot, such as a croton or an oak, has a stem or trunk made up of three layers.  An outer layer called the phloem (bark) an inner layer called the xylem (wood) and a very thin layer of cells in-between the phloem and xylem called the cambium.  The phloem, among other things, transports energy from the leaves to the roots.  This energy is packaged with auxins, or hormones, which tell the plant to make roots, and is sent to the base of the plant.  The xylem transports water and nutrients from the roots to the leaves.  The cambium produces both phloem and xylem.  As a tree grows, the cambium creates new layers of phloem and xylem.  The old layers of xylem are left behind and create the characteristic growth rings seen in mature trees.  



Cuttings:  This type of asexual propagation involves taking small cutting of a mature plant in order to reproduce that plant.  Cuttings work because when a cutting is made the phloem transportation is interrupted.  The energy that was packaged along with the auxins stops where the cut was made.  The auxins tell the plant to make roots and it does so in the spot where the cut was made.  

When taking cuttings, look for plant material about the width of a pencil and about 10 to 12 inches.  Cuttings should be made from only healthy plants and should be placed in a plastic bag immediately after being cut.  Water loss will be great if the cutting is left in open air.  After the cuttings are collected, they should be immediately potted.  Cuttings should be potted in one-gallon containers in pure perlite.  Before the cuttings are placed in the perlite, the lower leaves should be removed along with any flowers or fruits.  The lower leaves are removed so the plant can be placed easily into the perlite and the flowers and fruits are removed so they do not sap energy from the process of root generation.  If the cutting has a large mass of leaf area, about 1/3 of the leaves should be removed.  This is done so the plant does not lose an excess of water due to transpiration.  A fresh cut should be made at the base of the cutting.  The cutting should then be dipped in rootone.  Rootone is a man-made product that mimics the natural auxins.  Rootone will facilitate the production of roots.  After the cutting is dipped in rootone, place a pencil in the perlite in order to make a hole in which to place the cutting.  If the pencil does not clear the way for the cutting, the rootone may be scraped off when the cutting is placed in the perlite.  Once the one-gallon container is filled with cuttings (usually 3-5) the container should be placed on a mist bench.  A mist bench continually mists the cuttings keeping them moist and humid.  This is necessary because a cutting does not have roots to collect water.  Cuttings may be placed in a plastic bag to create a greenhouse effect, but this technique is far less desirable than the mist bench.  Once the cuttings have produced roots, they may be removed from the mist bench and individually potted into one-gallon containers.  These new plants can be grown in a protected area with dappled sunlight until the roots fill the containers.  At this point, the plants can be repotted into larger pots or placed in the ground.



Air-layering:  This type of asexual propagation has a higher success rate than cuttings because it allows the new plant to grow roots while still attached to the parent plant.  With air-layers, the phloem and cambium of a branch are removed while the xylem is left intact.  Similarly to cuttings, the phloem flow is interrupted which cause root growth at the cut.  The difference is that the xylem remains intact and allows water and nutrients to get to the affected branch.  The best time of year to do air-layers is in the spring or summer.

In order to make the initial air-layer, you need:  a healthy parent plant, a knife, moist sphagnum moss (place it in a bucket full of water, let it soak, and then drain out the water), aluminum foil (5” by 8”).

Multiple air-layers can be made on one parent plant.  Air-layers can vary in size and width from 12” long and 1/4” thick to 3’ long and 7” thick.  Smaller air-layers are generally more manageable than larger ones.  To begin, find a vertical branch on the parent plant about the width of a pencil.  About 12” down from the tip of the branch make a ring with the knife.  The cut should pierce the phloem, but not the xylem.  You will know when you hit xylem because it will be firm.  Make a second ring about 1½” from the top ring.  Then make a vertical cut that connects the two rings.  If the plant is actively growing, you should be able to place the tip of your knife in the vertical cut and peel away the phloem or bark.  This will leave you with a ring of exposed wood on your chosen branch.  It is then necessary to gently scrape the exposed wood in order to remove the cambium.  If the cambium is not removed, it will re-grow the phloem and roots will not form.  Because the phloem and cambium has been removed, energy bundled to make roots and bound for the root system will stop here and roots will grow at this point.  In order to facilitate root growth, place the moist sphagnum around the exposed area.  Before placing the sphagnum on the exposed area, gently squeeze it so it is moist but not wet.  Place a generous amount of sphagnum and hold it tightly in place with the aluminum foil.  This can be repeated many times over on the same tree in order to make multiple air-layers.  The air-layer is then left alone for 3-7 weeks to allow roots to form.  The air-layer should be checked after three weeks for root formation.  The foil can be gently pulled back to look for roots.  If roots have covered the sphagnum, the air-layer can be removed from the parent tree by cutting it just below the sphagnum-root mass.  Removed air-layers should be placed in a bucket of water and taken to a potting area.  The air-layers should be potted in well-draining soil.  In order to pot the air-layer, remove the foil from the newly formed roots.  Then, remove 1/3 of the leaves.  This will help the air-layer to retain moisture.  The air-layer should be potted in a two-gallon container with the roots placed below the soil line.  The soil should be carefully packed around the tender roots.  The air-layer should then be watered and may be given a liquid drench of a dilute solution of 20-20-20.  The air-layer should then be placed in a protected area.  A mist bench is preferred, but not as necessary as with cuttings.  When the new container is filled with roots, the plant may be repotted or placed into the ground.