CLONING - PLANTS FROM PIECES!
It is possible to grow a whole new plant from a tiny piece because plants possess TOTIPOTENCY; which means that every living cell of that plant contains the genetic information necessary for reconstituting all the plant parts and functions!
I think that is a pretty amazing capability; another wonder of nature! And not just because of the obvious advantage within the natural world, where ecological disasters need to be responded to; but also because of the possibilities that are provided to an observant plant propagator. Propagators talk about ‘taking cuttings’ and ‘striking cuttings’; but what we’re really doing is cloning a living organism.
One of the considerations that a propagator has to keep in mind is that the resulting plant will be an exact replica of the parent plant: which includes the age of the parent, and any inherent genetic tendencies. Therefore, choose your ‘mother plants’ carefully, and be sure that you know and like all the attributes of that plant. One of the distinct advantages of cloning is that the resulting plant will be more mature and bloom more rapidly than the same species started from seed. The only type of vegetative propagation that does not always result in a clone is a root cutting; there can sometimes be a deviation from the parent plant’s attributes, especially in the case of plants with variegated coloring in the leaf.
The drawback to cloning is the lack of genetic diversity, which keeps a species strong and vigorous, and better able to survive natural ecological disasters. Keep that in mind before filling your garden with multiple clones of just one ‘mother plant’!
In cloning plants we are taking advantage of adventious roots, of which there are two kinds. One type forms naturally on some plants; such as the brace roots on a monocot such as corn, or the aerial roots that form on a Banyan tree. The other type of adventious roots form in response to a wound. These are the type that ‘grow’ a plant from a cutting.
Each node, or bud, on the stem are sites of meristematic tissues that are necessary for the initiation of adventious roots. The first response to a wound on the stem is for scar tissue to form as a protection against pathogens. Then the cells in the vascular tissues begin to divide and initiate growth. This inherent ability varies in degree amongst plant species; some simply root more easily than others, and generally speaking, newer, fresher growth takes root more easily than more mature growth. Our job, as plant propagators, is simply to set up the life support systems needed to facilitate these processes !
LIFE SUPPORT SYSTEMS
To provide life support for a cutting you must control the water, oxygen, light levels, and temperature of the environment that the cutting is exposed to. It’s important to reduce unnecessary stress on the cuttings; those little ‘pieces of plants’ have a lot of work to do!
Water is necessary for uptake of nutrients within the plant tissues.
Water vapor and humidity helps to reduce the rate of transpiration.
Oxygen is necessary to enable tissue respiration, both around the leaves, and at the base of the cutting where missing tissues (roots) will be forming.
Low level, but bright light allows some photosynthesis to take place.
Temperature should be kept fairly stable, with the optimum range being 54 to 75 degrees. Cuttings may still root at a lower temperature; but it will just take longer.
To get the best advantage with cuttings, I think it is important to have a place already set up to root cuttings at all times; you never know when an opportunity to clone a plant might present itself. Shoots and stems can be accidentally broken while working in the garden, and you may wish to experiment with that bit of plant material. A gardening friend or neighbor might offer a cutting, or you may see something so beautiful growing along the street, that you simply can’t resist pinching off a little bit.
THE CLONING ENVIRONMENT
Some kind of an enclosing structure will help to maintain a more consistent atmosphere, and reduces stress on the cuttings. It can be as simple as a plastic bag suspended on stakes over a nursery pot or bucket; but then care must be taken that the plastic does not come into direct contact with the plant material. The propagator will have to make sure that the cuttings stay moist at all times, by misting at least once a day. Any structure used to contain cuttings should be set in a shady, but brightly lit place; if the area being used has too much direct sun, add a shade cloth cover over the plastic. Shade cloth that reduces the sunlight by about 50% is good. Commercial propagation units with plastic lids, and sometimes with built in bottom heat, are also available.
I have set up various ‘cutting environments’ by re-purposing structures or found equipment. One of my sons saw an old mortuary table being thrown away; and he right away realized his mother could find a really good purpose for it, and salvaged it! The table frame had a slightly sunken top, which was lined with metal pan about two inches deep, with a drain in one end. We simply added a frame structure, secured that to the table, and covered it with a heavy mill plastic that could be opened up on one side. We also installed a spray-misting system along the frame, and set it on a timer to mist the cuttings several times a day.
My current system was created from an awning that was removed from our house when we had it repainted. The awning frame is made of metal tubing, to which we secured a misting system, and then covered the whole thing with heavy mill plastic sheeting. The awning frame is secured to a bench built with a wooden frame and a metal screen ‘table top’; it also sits on metal legs which helps protect both cuttings and seedlings from predation by rodents.
A clean and sterilized one or two gallon nursery pot will work very nicely as a ‘cuttings bucket’. The two-gallon pots are about 8 or 9 inches in diameter and depth, which is good for larger or longer tip cuttings; I find that 11 to 18 cuttings fit in very nicely. Fill the nursery pot with clean, coarse pebbles or ¾” drainage rock up to about one and a half inches to insure good drainage. Make sure the pebbles or rock cover the drainage holes in the pot. Then fill the container to the top with your rooting medium; which needs to drain well, but retain some moisture at the same time.
I also use a ‘tray’ that is designed for use in an upward-migration Worm Bin. The trays I use are 16 x 16 inches, and about 4 inches deep; they are molded plastic with about 1/8 inch opening in a latticed bottom. I do not use any drainage rock at the bottom of this type of cuttings container. About fifty small or short tip cuttings will fit nicely, without over-crowding, into a tray like this.
One of the important things to look for when taking cuttings is the number of nodes and the spacing between them. At least three to five nodes on tip cutting is good; on some plants the nodes are very close together, on others they are spaced further apart. That’s why it’s best to have different depths and sizes of containers available for cuttings.
Be sure to label your cuttings with; species name, date the cuttings are struck, how many, and what type of rooting hormone, if any, you may have used. I have sometimes mixed species all in one container; but it is better practice to have cuttings of just one species in each container.
Some really basic components can be used in a variety of mixes and proportions. The mixture has to be sufficiently dense to physically support the cutting. It also has to be able to retain moisture without being soggy; and it needs to drain well enough to allow oxygen down to where the new growth is forming.
The basic components for a rooting medium are; perlite, vermiculite, peat moss, coarse river sand, pumice, and grit. The type of mix you use should be determined by the species you plan to clone, and also the type of watering or misting system you have in place. Avoid rooting plants in water; some plants will grow roots readily in water, but these ‘water roots’ often don’t survive the transition to soil.
A good, all purpose rooting mixture is equal parts of perlite, vermiculite, and peat moss. The perlite allows good drainage, the vermiculite retains a bit more moisture than perlite, and yet also drains well and provides some micro-nutrients, and the peat moss will keep the medium moist.
You can experiment with different mediums; some propagators use just perlite, some will mix sand in; some will mix peat moss with either/or perlite or vermiculite. Some people use just sand or pumice as a rooting medium, but then drainage is very rapid and you must have a misting system set up to keep the cuttings constantly moist. Whatever medium you decide to use, fill the cuttings container to the top. Wet the mixture thoroughly, then let it drain before ‘striking the cuttings’.
Don’t try to root cuttings in garden soil; it does work with some really easy to root species, but more often you will not get good results. Garden soil is full of micro-organisms, and possibly pathogens, that can easily overwhelm a cutting that already has a lot of growing to do.
There are also products on the market, such as rock-wool blocks that can be used to root cuttings. Each block is intended to accommodate one cutting, and the transition to soil is less stressful because there is less disturbance to the developing root system.
There are several different types of rooting hormones on the market, and they all seem to be equally effective. Most are based on the plant hormone Auxin, which is produced naturally in the apical meristem of a living plant, and controls many different growth functions.
Commercial rooting hormones can be either a liquid, gel, or powder. The dry, powder types often include a fungicide. The liquid types often require that the cuttings be watered several times with a solution of the hormone product. Some cuttings root so easily that no growth stimulant is necessary. Other species are difficult, and so sometimes it pays to experiment with different types of hormones and methods to get the best results. I like Olivia’s Cloning Gel, which I use at half strength. The prepared cuttings soak in the gel mixture for a short while before I ‘strike’ them into the prepared medium.
You can also make your own rooting hormone from fresh, young willow twigs. Simply soak the twigs in water for a day or two, and use this liquid as a dunk for the cuttings, and also to water them in. I have read that Comfrey (Symphytum officinalis) has some growth stimulants, and would like to experiment with that one day. The technique would be similar to that used with willow.
SELECTION OF CUTTING MATERIALS
Good selection, and the proper care and handling of your propagules will result in a higher success rate. Again, it pays to ‘think like nature’ and really observe the growth patterns and tissue conditions of the plant you wish to clone. When the plant is putting lots of energy into fresh, new growth, vegetative propagation will probably be easily accomplished. When a plant is mature, and its energy is directed into setting flowers or fruits, there will not be a lot of energy directed to vegetative growth. A mature shrub can be ‘prepped’ for cloning by pruning it to encourage new growth, and then utilizing this vigorous new growth for tip or greenwood cuttings.
Whenever possible, collect your cuttings early in the day; this is when a plant will have the highest water content in their tissues. Always select a healthy, un-stressed, and vigorous ‘mother plant’. Use a sharp, sterile knife or pruning shears to avoid damaging plant cells; and immediately wrap your cuttings in a moist paper towel, and then place them in a plastic bag. If you can’t process the cuttings until later, place them in a cooler, with an ice block. The cuttings, with stems wrapped first in moist paper towels, and then a plastic bag that does not enclose the foliage, will also keep in a refrigerator for up to a week.
Follow sterile procedures as much as possible, wipe your blade with rubbing alcohol in between taking cutting from various plants. Also work with a sterile blade when you’re preparing your cuttings.
TYPES OF CUTTINGS
Cuttings from various plants respond better at certain times of the year; with some experience it is easy to get a feel for it. A good rule of thumb is to think about where the plant is concentrating its energy; if the energy is in new growth, chances are cuttings will take; if the plant’s energy is in flowering or setting fruits, cuttings will be much less vigorous. Some plant species are just so easy to propagate they seem to grow anytime, and from any little piece !
Leaf cuttings - The cut leaf must generate both root and shoot; but even so, some plants are easy to propagate from a leaf ! Lots of succulents, begonias and streptocarpus can be propagated from leaf cuttings.
Herbaceous - Cuttings of succulents, and fleshy plants such as Pelargoniums, need to create scar tissue over the cut before they are placed in a moist rooting medium. This usually takes just a couple of days, and avoids the problem of plant material rotting in the rooting medium.
Softwood - Tip cuttings of new spring growth - these wilt easily, and are prone to bruising, and therefore rot.
Greenwood - A little later in the season; the growth is still young, but you can see the base of the stem darkening, and feel the stem firming.
Semi-ripe - The stems are harder, and buds can be seen developing at the nodes. Your cuttings will be from this year’s growth, such as dormant buds just beginning to swell, but the plant is not actively producing new growth at the time.
Hardwood - These cuttings are taken when the plant is dormant. Be sure to use a different cut – one angled across the stem, the other straight, so that you know which end needs to reach up to the light, and which one will grow down into the soil.
Layering - This process works really well for vining and caning plants. The ‘cutting’ is not detached from the mother plant; it may help to scar the tissue at a node, but often all you need to do is create firm contact between a node and the soil, and wait until roots have formed. When there is substantial new root and shoot growth, the clone can be cut from the mother plant.
Root cuttings - These are most often sections of root pieces, and the one type of cutting that does not necessarily produce a clone of the parent plant. Be sure when you take the cuttings that you will be able to determine which end was at the top, and which was growing down. If that’s not possible, lay the root cutting on its side.
Sometimes it just pays to experiment; you may have unexpected success; there’s much to gain, and not much to loose !
There are many reference books that provide lists of species with the best approach and time of year for successful propagation. The American Horticultural Society’s A to Z Encyclopedia of Plants lists propagation methods for every species covered! Other reference books are more specific to certain types of plants; and other books cover certain propagation methods in great detail.
PREPARATION OF CUTTINGS
Adventious roots arise from the nodes on the stem; the stem can be cut right below the node, or between two nodes. Remove all but two or three leaves, and if they are large leaves, cut them in half; this will help to reduce the moisture lost to transpiration. When placing the cuttings into the rooting medium I use a metal skewer, and create a long narrow hole to place the stem into; and then I firm up the rooting medium all around the stem. If you try to just push the stem cutting into the moist medium, you may break or damage the cutting. Also be sure to leave air space between each cutting; don’t crowd them in, this may encourage mildews to form.
Label your cuttings; I note the species, date, and number of cuttings struck, and if a rooting hormone was used. Then later when you pot up your rooted cuttings, note the date, and number, and any particulars such as pinching back.
The really important thing is to keep the cuttings moist, so be sure they are watered every day. Some leaves may drop, as the cutting is concentrating its energy in developing roots; be sure to remove any debris and keep the medium clean. Some cuttings will set roots within about two months, other species can take several more months to fully take root.
A VERY gentle tug on the stem of the cutting will give you an idea of the kind of root development that is taking place. To judge whether it is time to pot them up, also make note of any new leafy growth that is forming, and you might also want to remove a cutting from the medium and just take a look at the root development. If the roots are sparse, tuck the cutting back in place. If there are nicely developed roots, about two to three inches or so, the cutting is ready to pot up into a clean pot with a good soil medium.
Rooted cuttings need to be planted into a fairly light soil mix, and babied along for a month or so. When transplanting a rooted cutting try to keep a substantial amount of that medium around the new root system of the cutting, and transfer it all to the pot. Keep the newly potted cutting in the shade for about a week, and then gradually move it out into the type of exposure that the particular species requires.
A mild fertilizer, such as vermicompost tea, is ideal during this critical time. Pinch off the tip (apical meristem) of the newly rooted cutting to encourage growth from the less dominant lateral meristems and thereby create more growth at the sides, and a bushier plant.
Once the plant has established in the pot, we use a timed-release inorganic fertilizer such as Osmocote; but only in the container, never in the garden. As a dedicated organic gardener, I can accept this because there is no way a container can provide all the support systems found in healthy organic garden soil. The whole soil food web just cannot exist in a container, and thus many plants, especially natives, just don’t thrive in a pot. Many native plant growers that I have talked to say they have to utilize this process just to stay competitive.
Many plants, such as Buddleia, Lavatera, or any of a number of Salvias, can be large specimen plants within a year from cuttings. Remember; cuttings are ‘clones’ of the parent plant, and as such are of the same maturity as the parent, and will bloom much sooner than shrubs or perennial plants started from seed.