13 โ Propagation: Taking and Rooting CuttingsBesides using seeds, results of sexual reproduction in plants, we can propagate plants
asexually. This means taking cuttings from a mother plant and giving them the right conditions so they will become established, developing their own rooting system. Rooted cuttings are
clones of the mother plant, and hence they will share her genetic characteristics.
Different parts of a plant can be used for asexual propagation. Depending on the plant species and its maturity, you could propagate from growing tips, stems, leaves or even roots. Asexual propagation has several advantages, and it's particularly interesting for indoor gardeners in the optimization of time and resources. Among others,
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It's the fastest method to increase plant stock. Remember that plant growth is proportional to the capacity of the plant for photosynthesis, and the time required for rooting a cutting will be much faster than the time required to grow a plant of the same size from seed.
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Allows you to preserve good genotypes. Growers will propagate strong mother plants, with desirable genetics, and improve the output quality and yield of their garden.
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The results are fairly predictable. When growing from seed, you cannot be sure of what you are going to get. Propagating by cuttings will give you replicas of the mother plant.
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It's a great tool for disease and pest control. Cuttings are more resistant to pests and diseases than seedlings, and also allow you to select positively healthy plants in your garden.
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It allows you to experiment. Several cuttings from the same mother plant can be grown under different environmental conditions, or using different growing substrates and nutrients, to find out the optimal conditions for the species or strains you are growing.
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It allows you to acquire plants for your garden when you don't have seed. Cuttings can be collected outdoors during a hike or in a public park (of course, as long as it is legal) and brought home for growing. Also, cuttings are a great way to share plants between friends.
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Great synergy with pruning and harvesting. When shaping your plants, or when harvesting leaves, you can use the undesired plant parts as cuttings and waste a minimal amount of your plants precious matter.
Propagation of cuttings has many possibilities and different techniques, vastly exceeding the scope of this introduction. What I'm providing here is a basic outline of the method, taking the most common type of cutting as example.
Propagation through hardwood stem cuttings or leaves, and techniques like grafting or layering will not be covered in this post (although any contributions will be welcome as usual) and you're encouraged to learn further about alternative propagation techniques and visit the excellent specific tutorials in other threads of the forum, if you haven't done so already. Some good examples are
Ringworm's
Psychotria Propagation and
Caapi Propagation, or
Phalaris "Big Medicine" Propagation by
Ice House.
13.1.- When to take cuttingsThe first step to success in propagating cuttings is the
selection of a good mother plant. A suitable plant will be healthy and well established. We deal with stress better when we're stable and content, and plants are no different. Also, a strong, active mother will deliver healthier babies more able to thrive.
Time wise, it's important to choose a plant in its vegetative growth stage, and if there are seasonal changes in your indoor, pick a moment where the mother plant will be at full energy growth. Outdoors, this equals spring, when light hours are raising and plants are speeding up their growth. During the peak of vegetative period, plants are growing optimally and their ongoing metabolism will be carried on to the cuttings. You might try to take cuttings from flowering plants, but the chances of success are lower, their growth will be slower, and the time required to bring it back to vegetative growth will be a waste of resources and a source of stress for the cuttings.
If you want to prepare your mother plant before taking the cuttings, you can change her diet by decreasing nitrogen and increasing phosphorous and potasium. Lower nitrogen levels in the stem tend to speed rooting, phosporous promotes bushy growth and potassium helps to sustain it. So if you were feeding your mother plant in vegetative growth with a high-nitrogen NPK of 4:2:1 or more, switch to a balanced NPK a couple weeks before taking cuttings. Leaching nutrients from the soil a week before is also mentioned in some gardening guides, but I cannot vouch for it.
I take most cuttings at the first hours of the light period, to ensure that right after being planted they will have ahead a bunch of hours of energy delivery to enjoy and get to work.
Sometimes taking cuttings will not be a planned propagation strategy but a contingency tool instead, in order to rescue a piece of an infested leafy plant, or to save some stem from a diseased cactus for grafting. In those cases, extra care may be necessary to have it well established.
13.2.- How to take and prepare cuttings for rootingBefore anything, note that this chapter relies on the basic guidelines given in the previous section about
Pruning, so please check it out for simple practical hints and cutting techniques if you haven't read it yet.
Unless you are harvesting and disposing of the whole mother plant as you take new cuttings (and you shouldn't try that until you are positive that your cuttings will survive) keep in mind the pruning logic. You should choose viable cuttings whose removal will promote proper growth in the mother plant as well. Viable cuttings won't be too thin since those take much longer to root and have lower chances of survival, so in general and if possible, avoid taking cuttings with a stem thinner than 4-5mm.
For the procedure, prepare a good surface with enough light, and have everything you need clean and ready: Shears, scissors or razor, the destination container with the rooting medium ready (poke a hole in place if necessary) and moist enough, and optionally a container with water, rooting hormone (see below) and tools to apply it if desired.
In the classic growing tip cutting, the cut is made 45º against the stem, below a node (remember that nodes are growing spots, and that includes roots as well), leaving the apical bud and the pair of leaves below it, and pruning the remaining leaves, partially or completely. If you intend to bury the corresponding nodes in the lower pair of leaves, prune the leaves completely. If the lower leaves will stay above the ground, they can be trimmed to decrease water evaporation through their surface, particularly if the leaves are proportionally large. In this case make sure you don't damage the buds, since they will sustain new growth and branching once the cutting has rooted.
Once you've cut, as a rule of thumb, it's better to work fast to avoid air bubbles sneaking inside of the stem. Remember that the cutting's factories won't stop just because you severed them from the mother plant, and the pressure will keep sucking water up the stem. If there's no water, air will get in, and bubbles can form embolisms that might threaten the life of the cutting. A good way to prevent that is to have ready a glass or another container with spring or distilled water, and place the cutting inside as soon as it has been cut and pruned. You could also use damp paper towels for this.
New root tissue will be developed in the
phloem, the living, metabolically active tissue in the stem. Often, rooting will occur faster in spots where the phloem is exposed. After cutting, the phloem is only exposed in the lower end, and rooting may go faster if additional phloem tissue is uncovered. This can be achieved by removing the upper layer above the phloem, the epidermis of the plant, scraping very gently with a razor in the lowest part of the cutting. Only expose tissue that will be well under the rooting medium, and make sure you don't squeeze the stem if you decide to manipulate it. An obstruction in the stem vases due to excessive pressure will easily cause the death of the cutting. This scraping thing, however, is optional - but I've got great results with it.
We have seen previously that stems and leaves contain hormones called auxins, growth stimulants able to activate the rooting process. The application of several related compounds, generally labeled as
rooting hormones, is very useful to facilitate root production. In some plants, it will speed up the process; in others, it might be essential for success.
Rooting hormones can be found as a powder, a gel or a solution. Immediately after the cutting has been taken and pruned (or removed from the water / wet paper towel if you placed it there right after cutting), and before planting it in the rooting medium, the rooting hormones are applied to the spots where the phloem has been exposed (the lower end, any exposed nodes and any area that has been scraped with that purpose in mind). Avoid using excess, if you have soaked the end tip of the cutting in the rooting hormone powder, tap it gently to drop excess before planting. When using gel or liquid, I like to apply it with a clean little brush.
Finally, the cutting has to be placed inside of the rooting medium without forcing it or using excessive pressure, generally poking a proper hole before with a chopstick, at the proper depth. According to the size of the container, with available room for the roots to develop downwards and making sure that all the parts of the lower part of the cutting able to develop roots are in contact with the medium. This means not only the lower end of the stem, but any exposed phloem spots.
Once the cutting is inside of the medium, carefully pack the rooting medium around the base of the stem if possible, and water gently until the medium is evenly moist.
13.2.- Rooting and establishing cuttingsPlant cuttings, no matter how properly cut and handled before planting, experience shock. Applying some simple psychology to plant care is, again, important โ you want to make their life as easy and comfortable as possible until they recover. Otherwise, they will grow stunted under their possibilities, or they simply won't make it.
Successful plant propagation, as plant growing in general, strongly depends on environmental conditions. Proper soil, ventilation, temperature, light, and humidity will make the difference between a drooping, rotting cutting and a new healthy plant. The information in this section refers to regular, common cuttings composed by a piece of stem and a pair of leaves or two, unless stated otherwise.
Rooting MediumFollowing the general guidelines in the chapter about
Substrates, you could go with soil-based mediums (compost, peat, sand, loam...), soil-less mediums (perlite, vermiculite, rockwool, coconut fiber, arlite...) or a mix of the two. In either case, hygiene and sterility of the medium are essential here, particularly when working with slow-rooting cuttings.
Rockwool cubes and jiffy peat pellets have been widely used for rooting. Both are practical and can give good results. I personally reserve peat pellets for cuttings that root easily and explosively (like cannabis) and, as all-purpose rooting medium, I use a mix of 40% compost, 30% coconut fiber and 30% perlite.
As usual, remember that the medium should be spongy, not compacted. Air circulation is basic to prevent root rot.
LightGood fluorescent lights (CFLs, or T5 / T4 tubes preferably) are arguably the best and cheapest choice for rooting cuttings. They have a very good spectrum, they are efficient and they barely emit any heat, which allows you to place them just a few inches above the cuttings to maximize light use. Cool spectrum HID lights are a possibility as well if you have them already working, but the light intensity and the heat can be excessive so make sure the bulb is at least three feet above the cuttings, and keep a close eye on temperature and humidity. Also, when using HID lights, shading the cuttings under a cloth might be necessary to prevent burning in the leaves, at least until they have rooted. Personally, I would go with T4 fluorescent tubes. Two or more 20W T4 tubes, depending on the surface you need to cover, will work like a charm closely placed above the cuttings.
Regarding the photo-period, keep in mind that the cutting will be expecting the same amount of hours of light it was receiving when attached to the mother plant. Most growers will provide cuttings with a minimum of 18 hours of light, reaching the 24 hours in some cases since some cuttings may respond faster this way. But keep in mind that if you increase significantly the number of light hours to a long-day plant (see post about Lighting) or you decrease them to a short-day plant, you might accidentally induce flowering and that doesn't get along with the rooting process. So by default, put the cuttings under the same light period they had before in the mother plant, under vegetative growth.
Humidity and WateringAs long as your lights are in the proper range, water is the trickiest part to get right when rooting cuttings. Cuttings start with no root system and at first are very dependent on transpiration through the leaves, so you have to provide a humid environment. Steady CO2 uptake is essential for root growth, and if the environment is dry, the stomata in the leaves will close to prevent water loss and CO2 will not be captured. Once the roots develop, and water stress is reduced, ambient humidity can be progressively lowered until the normal growth levels, and a wider range of humidity levels is tolerated.
And while the new roots grow, the soil has to be kept moist โ if it's too dry, the fragile cutting will quickly wilt and die, and if it's too soggy, the tender new roots might drown or root rot might appear. The longer a species (or a particular plant part) takes to root, the longer you will need to be careful with water levels.
As the cutting roots, and as a general rule, ambient humidity should be high (90%) specially the first days, and you should water the cuttings every two or three days. You might do it more often if the humidity is low. Watering by misting is at this stage a good idea since it does not compact the soil.
For basic information about control of the atmosphere, you can refer to
chapter 7 in this thread. Humidity tents or domes, plastic bags, closed germination trays, humidifiers and regular fine misting can be all acceptable tools to keep the air around your cuttings humid. And in the first two weeks, this is vital for success, no matter which plant you are rooting.
TemperatureControlled heating of the growing medium, normally placing a heating mat or pad under the cuttings, facilitates the rooting process. Avoid using strong, unregulated sources of heat, and if possible leave a gap between it and the tray/pots to allow for some air flow. Keeping the base of the growing medium a few degrees above the air temperature will speed up rooting in most cases. 25ºC is adequate, and over 30ºC is generally overkill.
And the air temperature should be gentle (20ºC for not particularly cold-loving or heat-loving plants), and preferably not colder than the previous ambient temperature in the mother plant. If you want to root cuttings in winter, make sure your growing space is climatized.
Nutrients and CuttingsIf you are using a substrate rich in nutrients like compost, peat or other pre-fertilized mixes, you won't need to supply macro-nutrients for the first month or longer. Of course that depends on the size of the rooting container and the composition of your substrate.
When using non-soil substrates like rockwool or perlite, the basic nutrients will need to be added to the water. In this case, a balanced NPK proportion is usually adequate, with nitrogen not exceeding 75 ppm (parts per million). If you are using commercial fertilizers, do not apply them above the 50% of the suggested dose for the first weeks.
And whether you are using soil medium or using soil-less medium (but particularly in this case), when feeding or supplementing your cuttings keep in mind that available micro-nutrients are essential for a quick root development.
Generally, cuttings will take between one and three weeks to root. If you are using leaves or pieces of stem, the time might easily double. Once the roots are well established (once they poke visibly through the drainage holes, or through the sides of the rooting medium) the cutting is ready to be transplanted.
Ok - With this, we have finished the whole growth cycle of gardening indoors. I hope you have learned new stuff, and specially I hope you will be putting that stuff into practice.
When I have enough time to put them together in a decent way (and that takes a lot of time, since I do less copy-pasting than you might think), I will add the two remaining entries in the main index, by request: an overview of hydroponics and a practical summary of common pests and diseases, along with remedies and prevention.
Thank you for taking the time to read this, contribute anytime, and happy growing "The Menu is Not The Meal." - Alan Watts