Transcription
[Music]
I'm Harley Smith, and this is the Master Growers course. Today, we're going to start a series on plant propagation and cloning.
We're going to look at conventional ways of starting plants from seeds or from cuttings. A third way to start would be from tissue culture, or micropropagation, which involves growing plants in test tubes.
Now, that's going to be the way of the future for a lot of commercial production because growers will be able to produce an unlimited supply of clean, virus-free stock for their commercial production. But we'll save that for a future class.
Today, we're looking at conventional propagation with seeds and cuttings. Growers often ask me what's better: growing from seeds or growing from cuttings? If you're a breeder, the answer is both.
Plants grown from seeds are the result of sexual reproduction, involving a father and a mother. The genes are mixed, so it's like rolling the dice for genetics. No two plants grown from seeds are going to be exactly alike. Some will be very big plants; you'll get some monsters, some runs, some will have darker colors, or different aromas, or more potency with different aromatic oils, different terpenes, and different medicinal compounds.
Once you find that one special plant that has the characteristics you, as a grower, are looking for, that becomes the mother plant. You pick the best of the best according to your priorities.
Every plant grown from cuttings is genetically identical to the mother plant. So if you give it the same nutrients, the same light, and the same environment, you'll get the same results every time. The biggest benefit of growing from cuttings is reproducibility; you know what to expect every time.
Now, there is a downside if all you do are clones. Because they're genetically identical, sometimes there could be a genetic weakness that's hidden. For example, they could be genetically susceptible to powdery mildew. You won't know it until the conditions are right for powdery mildew, and then all of your plants get that.
So if you're a breeder, you want both. You want to continue to grow from seeds because there might be some hidden genetic strengths, like resistance to powdery mildew. Then you can cross it with plants that have the other characteristics you're looking for, come up with a new plant, a new mother plant with both superior characteristics, and that becomes the new mother.
Whether you're growing from seeds or from cuttings, first you need to choose a growing medium. There are several different choices depending on the method of growth. If you're going to be growing in soil, it's a good idea to use a starter soil to start your seeds or to stick your cuttings.
When you have a starter soil, you want to make sure it has very good drainage. You don't want the cuttings or the seeds to be sitting in a puddle of water because if they're in stagnant water, it sets up the environment for root rots that can happen right away.
Also, even if the surface is too wet, sometimes you'll get pythium right at the surface of the growing medium where it meets the stem. The plant can start to grow up and then fall over with the fungus; it's called damping off.
So make sure that it's a moist growing medium if you're growing in soil or in any other growing medium, but not overly wet—not saturated with moisture.
Seeds need water to germinate; they need moisture and oxygen. That's why you want the good drainage—not a puddle. They also need warmth. If you provide those three things, you can start your seeds.
If you're going to grow in soil, another benefit would be to inoculate the soil right from the very beginning, even when you plant the seed or stick the cutting, or at least at transplant, with beneficial microorganisms.
If the plants start out weak with just a few little stringy roots, they're not going to do as well as if they have a massive, strong, healthy, white, feathery root system. The proper microorganisms can make that possible.
Another growing medium, if you're going to use soilless mixes like peat or other soilless mixes, would be plugs—either peat plugs or plugs from composted wood. They hold together better; they're spongy, they hold water, and they hold moisture.
You don't have to oversaturate them, though, because they're already like a sponge. If you take out a growing cube and give it a little squeeze, if you see just a couple of drops coming out, it's wet enough; it's ready to go. It doesn't have to be soaking wet.
So they're very easy to use and easy to handle. Also, they hold the roots together better. When using soil or soilless mix, it can be kind of messy as you're transplanting. You're going to break some of those microscopic root hairs, and that could open up the plant to infection.
But if you use the plugs, they're holding together, so you won't damage as many of the microscopic root hairs that way. Another benefit of the composted barks and the peat is that they're already composted, so they have microorganisms already there—plant growth-promoting rhizobacteria—just naturally.
That doesn't mean we can't give them some of the superstars to improve rooting and root strike even more, but at least they're there from the beginning.
Now, the third growing medium, especially for hydroponics, that I prefer when I want to start clean and keep it clean is rockwool. I don't want to bring soil-borne pests and diseases into my grow room.
I like to start with rockwool. Rockwool is actually made from rocks—Baltic rock limestone. They're crushed, melted, and then blown into spinning cylinders, just like making cotton candy. Have you ever seen cotton candy made at the fair? Well, rockwool is made the same way.
Then it's compressed into different shapes, including starter cubes. One sheet of starter cubes fits perfectly into a standard nursery tray, and you can choose it in different sizes. If you're going to do seeds, you might want 98 starter cubes to start with. If you're going to do cuttings, it might be better to have 50 to give them a little bit more room for the plants to grow.
Either way, it fits in a standard nursery tray. One of the weaknesses of rockwool, at least in the past—though I know there are some new manufacturing processes and new factories being built that have solved the problem—is that rockwool was a little bit alkaline coming right out of the package because they use a little bit of limestone in the manufacturing process.
So the first time you use the starter cubes, you're going to want to condition the rockwool. It's very easy: just adjust the pH. Lower the pH to about 5.5. Take two gallons of water, lower that pH, and maybe add a small charge of nutrients, like a full-spectrum hydroponic formula.
It doesn't have to be strong; it could be quarter strength—just a little bit of trace elements. That way, pour it over your standard rock starter cubes in the standard nursery tray until it's completely submerged. Then pour off the excess water so it's not sitting in a puddle, the same way as you would in soil.
Once it drains, just put a seed in each hole or stick a cutting in each of the pre-drilled holes. Once you've done that, cover it with a humidity dome. That'll keep the relative humidity at about 98% under that dome—ideal conditions for germinating seeds and for rooting cuttings.
You can have a smaller dome if you're doing seeds, or taller domes that you can use for doing cuttings. Another thing that is beneficial—though not necessary, but recommended—is to slide your tray onto a heat mat.
The heat mat will just provide a little bit of extra warmth at the root zone. Now remember, to germinate seeds, they need water, oxygen, and warmth. So if they're tropical seeds, like tomatoes or peppers or some of the medicinal herbs, a little bit of bottom heat will be beneficial.
It'll help the seeds germinate more quickly and start to grow; it won't take as long. I've planted seeds sometime Friday night before I left for the weekend, and when I come back on Monday morning, the seeds are already germinated, and the plants are starting to grow.
The next step is providing light, even for the seedlings. Now, the large tropical seeds don't need light to germinate; they have enough stored carbohydrates and minerals from the mother to start to grow and reproduce.
Small seeds, though, like lettuce seeds or spinach seeds, don't even have enough carbohydrates; they need light or they won't even germinate. Our tropical plants could germinate in the dark, but still, I like to put them under fluorescent lights—full spectrum.
I want to make sure I have a little bit of light so when the seed cracks and that embryonic plant starts to grow up, I want it to see the sky right from the beginning. I want it to see the light because if it germinates in the dark, it may want to start to stretch.
If those seedlings get tall and spindly, it weakens the plant; they can fall over with damping off, or they might not even produce as well later on. So I want them to be short and stocky, seeing the light right away.
Full spectrum light, especially with the blue end of the spectrum, is important. Plants have evolved to compete for light; they want to see the sky. If they're in the shade, they're going to want to stretch to get above the other plants, or they want to lean toward a break in the canopy.
So once they come up and see the light, I want them to see the sky. They'll stay short and stocky, with thicker stems and more dark green foliage because blue is responsible for chlorophyll production more than any other color in the spectrum.
The cuticle cells, the waxy covering on the leaves, will be thicker even on those baby plants or those young clones. They'll be more resistant to fungi and more resistant to drought just because they have smaller cells with thicker cell walls.
The stomata, the pores that take in CO2, will be denser and closer together if you have plenty of spectrum light with blue as part of the spectrum. If you look at the leaf under the microscope, you'll see it for yourself.
It turns the plant into a photosynthesis machine, and that's what we want from the very beginning. If we get a strong head start, it'll pay us back many times over by the time we get to harvest.
I also personally like to leave those lights on at the very beginning, 24 hours a day, instead of turning them off. Now technically, all we need is about 14 to 17 or 18 hours, but I want to have light there in case any of the seeds germinate.
So I'll leave it on 24/7. It also adds more even temperatures. You know, if the lights are on and they warm up, then you turn the lights off, everything cools down. I prefer to see more constant humidity and more constant temperature, especially for those little baby plants that are just getting established.
Once they start to get established and growing, I'll take off the humidity dome first of all so fresh air can come in for more CO2. Also, it takes away the environment that would be conducive to fungus. High humidity could grow fungi, so we want to at least crack that humidity dome open or even remove it.
At any time after that, you could go to 18 hours a day if you like. At the beginning, I want them to start out strong. So when it comes to lighting, I'll just put four fluorescent bulbs over my standard nursery tray, keeping it just a few inches above the growing tips because it's not that intense and not that warm.
Then I raise the light as the plants start to grow; they'll be short and stocky that way. Next comes transplanting. Now, how do you know it's time for transplant? I know beginners are often impatient; they want to lift it up and see if there are roots yet.
But my suggestion is: don't disturb those roots. If you disturb them a little bit, you're going to break some microscopic root hairs, and you're going to start to shock the plant. So it's going to want to recover from the disturbance.
You're better off just to wait until the first true leaves appear. The first leaves that you see are the embryonic leaves—the ones that were inside the seed when you're starting from seeds. The next set of leaves are the plant's true leaves.
Once you see those leaves appearing, you know that the plant is actively growing; you have actively growing roots. It's going to start to need a little bit of nutrition from the outside environment, and it's a good time to transplant.
You can wait a while if you're not ready to transplant, but at the minimum, wait until you see at least one true set of leaves before transplanting.
Once you transplant your seeds or rooted cuttings, you want to concentrate the growth—the energy of growth—into rooting. You don't want to stimulate a lot of early growth. First thing, you don't want spindly plants; you want a good root mass, more lateral root growth, and a sponge of roots that'll help the plant take up water and nutrients.
That's where adding a little extra full spectrum light comes in handy too. The red end of the spectrum actually stimulates root development. So I want a lot of blue, a little bit of red mixed in, and I want to steer the energy of the crop toward root production in those first few weeks.
The first thing to do to improve rooting is to use a full spectrum nutrient that contains phosphorus. Phosphorus is the energy element; it energizes rooting and flowering as well.
But early on, if we add just a little extra phosphorus to the root zone, we change our fertilizer into a starter fertilizer. You'll get better root strike and better establishment of the plant; it channels the energy into making more roots.
One of the best forms of phosphorus to use early on, just those first two or three weeks after transplant, is monoammonium phosphate. It adds some nitrogen with the phosphorus, and the ammonium actually aids with the uptake of the phosphorus by the plant.
Also, the ammonium form of nitrogen those first few weeks is the preferred form of nitrogen because when the plant assimilates it, it's right in the roots. It's immediately changed directly into amino acids and into enzymes, into chlorophyll, to activate the energy and the chemistry of life.
So a little bit of monoammonium phosphate can lead to as much as 20% more roots at transplant. If you're growing in soil, it's a little bit different. If you're going to be using organics like rock phosphate and bone meal, again, you want to inoculate the roots with the mycorrhizal fungi and the phosphorus-solubilizing bacteria right from the very beginning—right from your very first transplant.
The mycorrhizal fungi infect those new growing roots in a beneficial way. As the fungi grow in the root zone, as the mycelium mass goes out in the hyphae, they're making organic acids. The fungus is making enzymes that unlock phosphorus from the soil and from organic matter and feed it to the plant.
So again, phosphorus becomes more available, leading to better root strike and better establishment right from the very beginning. As the roots grow, the fungi and bacteria are going to grow along with them.
The next thing to keep in mind to stimulate more root growth is the availability of some of the trace elements—the microelements—such as iron, copper, manganese, and zinc. They activate enzymes that are used for cellular metabolism to make more root cells, so those need to be available right from the very beginning.
For example, zinc is a co-actor that turns on enzymes to make the rooting hormone called indole-3-acetic acid (IAA). Zinc activates the enzymes to make growth hormones by the plant, so zinc has to be there in a very small amount, but it has to be available to the plant.
One of my recommendations early on is to make sure the pH is in the correct zone right from the beginning. If you're growing in hydroponics, keep the pH on the low side—somewhere between about 5.8 and 6.4. If you do, all the elements are available to the plant all the time.
If you get above 6.5, iron starts to become unavailable. We could put it there, but the plant can't use it. If you get above 7.5 pH—that's just barely alkaline—your water might be more alkaline than that. If it's above 7.5, all those transition metals start to become unavailable to the plant: iron, copper, manganese, and zinc.
So watch your pH right from the beginning, especially in hydroponics. In soil, make sure your soil is pH buffered, that the pH of your soil is somewhere in the range of maybe 6.4 to 6.8—slightly acidic to start with.
Soil is a buffer for pH, so it doesn't change very often. It's not easy to change the pH of soil. I know farmers that add lime by the ton, by the truckload, to acid soil, and it's still not enough.
If you're growing in water, it just takes a few drops to adjust your pH. So you want to make sure your bulk soil is perfect right from the very beginning. Make it more conducive to the microorganisms, and then the microorganisms will, as they grow on the roots, lower the pH in the root zone to the perfect level to take up those trace minerals.
Next thing to keep in mind is to keep the water temperature or the root temperature in just the right zone—somewhere between about 68 and 75 degrees. Remember, when you are germinating your seeds or starting your cuttings, 78 degrees was good.
But the warmer the water, the less dissolved oxygen it'll hold. So at the beginning, 78 is almost ideal, but once they're germinating and the roots are actively growing, you want to lower the temperature just a little bit.
If it's too high—if it's 78, 80, or 82 degrees—you're rolling the dice for root rots. Remember, root rots are the anaerobic fungi; they grow in stagnant water without oxygen.
I've seen cuttings that are growing in aeroponic systems, where the roots are suspended in air, still get root rot—get slimy and brown. Why? Because the temperature was too high.
So if you want to be really safe, shoot for about 72 degrees. If you want just a little bit more root growth, warm it up to about 75 degrees. But be careful; if it gets too high a temperature, you're going to set up the environment for root rot.
On the other side, if you have too cold of water or too cold of a root zone, it starts to shut down the enzymes for cellular metabolism. Cellular metabolism makes the roots, so that could shock the roots too and prevent them from growing.
Keep the temperature in the right zone, and you'll have abundant lateral root growth and root mass.
Okay, so now you've established the correct balance of nutrients, you have the right pH, the right temperature, and good oxygenation. This is the time to add just a little bit of a root stimulant.
Now, if you look at the root stimulant products on the store shelves, you're going to see a common theme: kelp extracts. It may not say kelp; it may say Ascophyllum nodosum, which is a brown seaweed from the littoral zone. It's loaded with natural rooting hormones—auxins and cytokinins, even gibberellic acids.
In fact, if you have some seeds that are a little bit old or maybe they weren't stored quite properly, it's a good idea to soak them overnight in a kelp extract. They'll have earlier germination and a better germination rate.
But what we're talking about now, once you have roots, is to use it as a root drench. The auxins stimulate lateral root development, and the cytokinins stimulate cell division.
So the combination of the auxins and the cytokinins stimulates more lateral root growth and more root mass. To make it even more effective as a rooting tonic, add a little bit of humic acid.
We've seen side-by-side trials from Virginia Tech where the root mass doubled or even tripled by combining those two ingredients together. That 5:2 ratio also stimulates the plants to make a plant protection agent called superoxide dismutase, which protects the plant against stress—against heat stress, drought stress, salt stress, and UV stress from the lights.
So if you can condition those young seedlings against stress, not only do you have more root mass to take up water and minerals, but you also have more plant protection agents. The plants will stay green longer and recover faster if they go into some transplant shock.
Finally, almost every root stimulant product on the market includes at least a little bit of B vitamins, especially vitamin B1. A high dose of vitamin B1 stimulates the plant's systemic induced response. In other words, it primes the plant; it puts it on high alert.
So if it comes under attack, say by a root pathogen, the plant's natural immune system responds very quickly. It's primed; it's ready for problems; it's ready to react.
The best time to add a little B1 is before transplanting because no matter how carefully you are in your growing medium, when you do your transplanting, you're going to start to break some of the microscopic root hairs. That opens up the plant to infection by some of the root rots, like pythium and Rhizoctonia.
But if you've stimulated and sensitized the immune system, you break a few of those root hairs, and if it starts to come under attack, the plant will respond quickly, and it'll recover more quickly, continuing to make clean, healthy roots.
By the way, you could use the humic and fulvic acids in the kelp even as a foliar spray on your clones. The auxins, the IAA, are made by the plant in the leaves; they're not made in the roots.
So if you're starting to have a few rooting problems, if rooting is too slow or you have a little root disease, use a foliar spray. The tonic will transport the auxins in an exchangeable form into the leaf tissue, giving the plant a little burst in the right direction.
Let me tell you a story. One time, a friend of ours gave us some prime clones from a thoroughbred stock with some superior characteristics. It was unusual; they just wanted to share those genetics with us as a gift.
So we got them from up north. They took the cuttings from plants that were a little bit too young; they were still just in the beginnings of vegetative growth. Personally, I'd like to see plants that are at least two months old as mother plants so they have more stored energy.
These were a little bit young—just a little bit weak in their growth. So they took the cuttings, we put them into 4-inch rockwool blocks to get them to root well, we brought them home, and we put them under lights.
We waited; a week went by—nothing. Ten days went by—nothing. The leaves started turning yellow at the bottom; they started falling off. My wife came in and said, "Harley, what are we going to do? We need to save these clones!"
I took one look at them and said, "Oh, start over; these are never going to be good producers." She goes, "No, no, no! These are the only ones we have; we can't replace them."
I said, "Okay, what would I do?" Oh, my own advice from science from Virginia Tech: five parts fulvic acid, in that case, two parts kelp, and added a little bit of yucca as a wetting agent.
We did one fine spray—just one mist on those leaves. I'm not exaggerating here; I'm telling you the truth. Two days later—two days—roots were bursting out the bottom of those cubes. The plants recovered, and they were all good producers.
So you can make your own tonic too. Use it at the leaves or use it at the roots. If you mix up a fresh batch to use as a foliar spray, when you're done, don't store it on the shelf for two or three weeks.
Take what's left over and pour it right over the root drench. It'll stimulate root growth to take up the nutrients and also stimulate the production of the hormones for the plant.
I only had to do it once because once we primed the plants and gave them that little burst, that head start, afterwards they were doing photosynthesis, taking up water and nutrients. They made their own B vitamins; they made their own auxins.
So it only took a little bit of a push in the right direction.
Thanks for attending today's class on plant propagation and cloning. I hope you enjoyed the class, and I hope you've learned a few tips to improve your garden. I also hope to see you in future classes.