The fate of weed seeds in the soil has been an area of much research in recent years. Most studies have focused on the seeds that successfully produce seedlings since these are the seeds that cause immediate problems for farmers. In most studies, annual emergence typically accounts for 1 to 30% of the weed seed in the soil. Thus, the majority of seeds found in the soil seed bank fail to produce seedlings in any given year. To know more about the different parts of the cannabis plant will facilitate cultivation and help us achieve better results. In this post we explain t In this series, we hope to explain all the pertinent Cannabis plant facts at-a-glance. Start educating yourself on the Cannabis plant.
Fate of weed seeds in the soil
The fate of weed seeds in the soil has been an area of much research in recent years. Most studies have focused on the seeds that successfully produce seedlings since these are the seeds that cause immediate problems for farmers. In most studies, annual emergence typically accounts for 1 to 30% of the weed seed in the soil. Thus, the majority of seeds found in the soil seed bank fail to produce seedlings in any given year. The fate of seeds that fail to germinate and emerge is poorly understood. While some of these seeds are simply dormant and will remain viable until the following year, others are lost due to decay or consumed by insects or small animals. This article will describe results of an experiment that monitored the fate of seeds for the first four years following introduction into the soil.
Methods: Seeds of velvetleaf, waterhemp, woolly cupgrass and giant foxtail were harvested from mature plants during the 1994 growing season. The seeds were cleaned and counted and then buried in the upper two inches of soil on October 21, 1994. Two thousand seeds were buried within a 3 sq ft frame to allow recovery during the course of the experiment. Weed emergence was determined by counting seedlings weekly during the growing season. Emerged seedlings were pulled by hand after counting. In the fall of each year one quarter of the soil within a frame was excavated and the remaining seeds were extracted and counted. Corn or soybeans were planted between the frames during the course of the experiment to simulate agronomic conditions.
Results: The emergence patterns of the four species were described in an earlier article (see emergence patterns). The fate of the seeds (emergence, loss or survival in soil) during the first four years after burial is shown in Figure 1. In the first year following burial waterhemp had the lowest emergence (5%) whereas greatest emergence was seen with woolly cupgrass (40%). Total emergence over the four years ranged from 300 seedlings (15% of seed) for waterhemp to 1020 seedlings (51%) for woolly cupgrass. More than three times as many seedlings emerged in the first year than in subsequent years for velvetleaf, woolly cupgrass and giant foxtail, whereas 140 waterhemp seedlings emerged in 1996 compared to only 100 in 1995.
Figure 1. Fate of seeds during the four years following burial in the upper two inches of soil. Two thousand seeds of each species were buried in the fall of 1994. The area in white represents the number of intact seeds present in the fall of each year, green represents the total number of seeds that produced seedlings during the four years, and the blue represents the total number of seeds lost. Buhler and Hartzler, 1999, USDA/ARS and ISU, Ames, IA.
Seeds of the two grass species were shorter lived than those of velvetleaf or waterhemp. At the end of the third year (1997) no grass seeds were recovered. Somewhat surprising is that waterhemp seed was more persistent than velvetleaf in this study. Velvetleaf has long been used as the example of a weed with long-lived seeds. In the fourth year of the study four times more waterhemp seedlings than velvetleaf emerged and four times more waterhemp seed than velvetleaf seed (240 vs 60) remained in the seed bank.
For all species except woolly cupgrass the majority of seeds were unaccounted for (the blue portion of the graph) in this experiment. Determining the fate of the ‘lost’ seeds is a difficult task. A seed basically is a storage organ of high energy compounds, thus they are a favorite food source of insects and other organisms. In natural settings more than 50% of seeds are consumed by animals. The importance of seed predation in agricultural fields is poorly understood, but recent studies have shown that predation can be a significant source of seed loss. Another important mechanism of seed loss likely is fatal germination. This occurs when a seed initiates germination but the seedling is killed before it becomes established. Fatal germination probably is more important with small-seeded weeds such as waterhemp and lambsquarters than with large-seeded weeds, but is poorly understood. A better understanding of the factors that influence seed losses might allow these processes to be manipulated in order to increase seed losses.
So what does this mean as far as managing weeds in Iowa. First, consider how the methods used in this experiment might influence the results. The seeds were buried in the upper two inches of soil, the zone most favorable for germination. Most long term studies investigating the persistence of seeds have buried the seeds at greater depths than used here in order to minimize germination. If the seeds were buried deeper one might expect less emergence and greater persistence since the seeds would be at a soil depth with less biological activity. If the seeds had been placed on the soil surface it is likely that there would be more predation, less emergence and shorter persistence.
The results indicate that the seed bank of giant foxtail and woolly cupgrass should be able to be depleted much quicker than that of the two broadleaves. Maintaining a high level of weed control for two years should greatly diminish populations of these weeds in future years and simplify weed management. Unfortunately, a single plant escaping control can produce more seed than was introduced to the soil in these experiments, thus the seed bank can be rapidly replenished any time weed control practices fail to provide complete control. Finally, over 50% of velvetleaf and waterhemp seed was lost in the first two years following burial. However, significant numbers of seed of these species remained four years after burial. This will make populations of these two species more stable over time than those of woolly cupgrass and giant foxtail.
Doug Buhler is a Research Agronomist at the National Soil Tilth Laboratory, USDA/ARS, Ames, IA.
Anatomy of the Cannabis plant
When it comes to cannabis, the part of the plant that gets all the attention is naturally the bit we’re all growing for: the flowers. But while it’s easy to be enamoured with the beautiful frosty flowers we shouldn’t overlook the rest, because behind the bud there’s a whole plant, with all its component parts, each playing an essential role in bringing us our precious harvest.
Here at Alchimiaweb we strongly believe that the more we know about our favourite plants, the more success we’ll have cultivating them, and the happier we’ll be with the results! For these reasons here we’re going to take a closer look at the cannabis plant and identify all the different elements of its anatomy to help you get to know this wonderful plant a little bit better.
1, male flower, enlarged detail; 2, pollen sac; 3, pollen sac; 4, pollen grain; 5, female flower with bract; 5, female flower, bract removed; 6, female seed cluster, longitudinal section; 7, seed with bract; 8, seed without bract; 9, seed without bract; 10, seed cross section; 11, seed longitudinal section; 12, seed without hull (Franz Eugen Köhler 1887)
The Cannabis seed
For most of us, our introduction to cultivation comes when we buy or are gifted some cannabis seeds for the first time, so let’s set out on our examination of cannabis anatomy starting with the seed.
A healthy, mature cannabis seed will be well-rounded in shape with one pointed end and one flat end. They have a tough outer casing that is rigid to the touch, preventing the seed from being easily crushed. A seam separates the two halves of the shell (also known as the hull or pericarp) and is where the seed opens during germination.
Depending on their genetics, seeds can vary greatly in size, from really tiny (800 seeds per gram) to absolutely massive (15 seeds per gram). In mature seeds the outer shell should be covered with attractive dark markings known as “tiger stripes” which, like snowflakes, are unique to each seed and are in reality a thin layer of cells coating the seed and can be rubbed off easily, revealing the true tan/beige colour of the seed beneath.
Detailed view of a cannabis seed
Inside the seed we will find the embryo of the plant, everything needed to start a new life, dormant until the right conditions of moisture and warmth are met. We have the root, or radicle as it’s known while still in the seed, the cotyledons, those first, fat, rounded embryonic leaves containing the seed’s food reserves for early development. Cannabis is a “dicot” plant, meaning it has two cotyledons. Situated in between the cotyledons, surrounded by the first two true leaves is the apical tip, the point from which the plant will continue growing once germinated.
When we germinate a cannabis seed, the first thing that emerges from the opened seed will be the tap root which will begin to grow downwards, seeking out moisture and nutrition and colonising the substrate. The root system has three main purposes, not only does it anchor the plant in the substrate, it provides it with water and the nutrients, and it also acts as storage for sugars and starches produced by photosynthesis. It’s hard to overstate the importance of the roots in cannabis cultivation, they really are the foundation upon which everything else is built, without healthy roots we won’t harvest beautiful flowers!
Roots themselves can be classified into three types. Firstly the tap root, which is the principal component of the root system, the subterranean counterpart to the plant’s main stem, pushing vertically downwards and shooting off branches as it grows. These branches are the second type, the fibrous roots, which branch off from the tap root, extending outwards to form an underground network approximately the same size as the aerial part of the plant. A third type of roots are known as adventitious roots, these are the thick roots that sometimes sprout from the stem just above ground. These are the roots that make it possible to reproduce plants by taking cuttings and cloning them.
Adventitious root growing from the stem of a clone
Cannabis plants grown from seed will start life with a tap root system that develops into a fibrous root system, while clones don’t have a tap root, starting instead with adventitious roots before developing a fibrous root system. In all cases, a root system needs an adequate balance of moisture and air to be healthy and if care and conditions are right we will be able to see thick, bright white roots with plenty of fine hairs when we transplant.
The root crown
The part of the plant where the roots and stem join is called the root crown, or sometimes collar, or neck. This is a vital part of the plant, the dividing line between upward and downward growth, where the vascular system switches from roots to stem, and one of the places in the plant where most cell division takes place.
The root crown is naturally situated very close to the surface, where aeration is at its most, however some growers will transplant with the crown buried well below the surface, which encourages adventitious roots to sprout from the buried section of stem. It’s good way to deal with those leggy seedlings that stretched to get to the light and ended up too tall.
Stem and nodes
The stem of the cannabis plant is the part responsible for keeping the plant upright and for supporting the weight of the plant. It contains the vascular system which works to carry moisture and nutrients from the roots to the leaves via xylem cells, and to transport the sugars and starches produced via photosynthesis around the plant for use or storage via the phloem cells. Phloem is otherwise known as bast, the part of the cannabis or hemp plant that is traditionally harvested for fibre to make rope, canvas etc.
Cross section of stem showing a node
The stem, which can sometimes be hollow, is divided by nodes where the lateral branches begin, with the space between them being known as the internode. Seedlings will begin by growing opposite pairs of nodes and leaves but as time passes the nodes will start to grow alternately, sign the plant is mature and ready to flower.
Taller, stretchier Sativa plants will have a larger internode spacing than squat, compact Indica varieties, although environmental factors can also influence internode space. The nodes are where the first flowers appear (pre-flowers), so it’s the first place growers look when trying to determine the sex of plants grown from regular seeds. The small, narrow spear-like leaf growing at each node is called the stipule, and shouldn’t be confused with pre-flowers.
Nodes are one of the parts of the cannabis plant where most growth happens and most hormones are produced, for this reason we always cut clones with at least one node to be planted below ground in the substrate, so it can produce auxins (rooting hormones) to begin root development in the undifferentiated meristem cells of the node.
Leaves and petioles
Cannabis leaves are palmately compound (shaped like the open hand, with multiple parts), with anything from 3 to 13 veined, serrated leaflets or fingers. Indica varieties will generally have wider and shorter leaflets of a lush dark green colour, but fewer in number, while Sativas will have longer, narrower leaflets and can be of a lighter green shade. Of course, cannabis is a hugely diverse genus and there are exceptions to this rule, most notably the Ducksfoot variety, with its webbed leaves. Autoflowering varieties will tend to have smaller leaves, with the shape depending on the individual genetics, but as a general rule leaning more to the Indica side.
Leaf and structure comparison of the different cannabis species
A cannabis plant will have large and small fan-type leaves, which we remove and dispose of at harvest time, and also sugar leaves, which are the small, resin-covered leaves that protrude from the bud. These will either be trimmed away and kept aside for resin extraction, or simply left on the bud and smoked with the flowers.
Leaves from two different hybrids
As a seedling grows, each set of leaves has an increasing, odd number of leaflets, so the first set of leaves above the cotyledons will almost always have a single leaflet, the second pair will have three, the third will have five and the fourth will have seven leaflets, and so on until the plant reaches the usual number as dictated by its genetics.
The leaflets join at the point known as the rachis, from where they attach to the stem or branch by a leaf-stem known as the petiole. Petioles can be of varying length depending on the variety and can naturally vary in colour from green to dark purple, although in normally green plants a purple petiole can often be a sign of a phosphorous deficiency.
The fan leaves function both as solar panels and air conditioning for the plants, with the darker green upper side of the leaf producing energy via photosynthesis and the underside regulating internal processes via stomata, tiny pores that absorb the CO2 needed for photosynthesis and at the same time release water and oxygen. The stomata will close at night to conserve moisture and during the day will respond to heat and humidity levels, opening and closing to constantly balance internal moisture levels with external environmental conditions and keep metabolic functions working.
Cannabis is dioecious, meaning the male and female reproductive organs are on different plants. Unless we’re planning on doing some home breeding and making seeds, we won’t be growing any male plants to full maturity, but it’s important to be able to identify them, even if we’re growing exclusively from feminised seeds, just in case.
Female pre-flowers on the left, male flower cluster on the right
The male, staminate flowers effectively resemble green balls on sticks, composed of five petals which open to reveal five pollen-producing stamens. They grow in long, loose bud clusters from internodes on the branch and once pollen is released the male plants will soon die off. Male flowers contain low levels of cannabinoids and terpenes.
Female pistillate flowers are formed of tight clusters of bracts, the small, teardrop-shaped green petals that we growers refer to as calyxes. Each bract or calyx contains the ovary and the pistillate hair or stigma, which is what growers call the pistil and is the part of the flower that catches airborne pollen. Once pollen lands on the stigma, it is transported down the pollen tube to the ovary where fecundation takes place and the seed is formed, filling and swelling the bract as it grows. The thick, white pistil or hair will shrivel and turn a brown or red colour one it has served its purpose. The seeds are usually mature after a further 4-6 weeks time.
Both cannabis flowers and leaves develop beautiful colours
After pollination, female plants will devote their energies towards seed production, at the expense of resin. This means that seeded buds will have lower levels of cannabinoids and terpenes, and is one of the main reasons we strive so hard to grow sinsemilla (seedless) flowers, quite apart from the awful taste of smoking a seed in a joint!
Trichomes clustered on a bud
Botanists are still unsure as to exactly why cannabis plants produce such a large quantity of trichomes, but most agree that they most likely have the function of protecting the flowers and developing seeds, whether from harsh UV light, insects, grazing animals or extremes of temperature.
Trichomes have two different basic types: Glandular and non-glandular, with the principal difference being that non-glandular trichomes grow without a trichome head or gland, having the appearance of small hairs and mainly developing on stems, leaves, petioles and to a lesser extent on the flowers themselves, while glandular trichomes are found mainly on the flowers and sugar leaves, and possess the resinous gland where the cannabinoids and terpenes are secreted.
Glandular trichomes under the microscope
Glandular trichomes are themselves divided into three main kinds, which are: bulbous, the smallest and least numerous; capitate-sessile, which are larger and grow low, close to the leaf surface; and finally capitate-stalked, which are the largest, most numerous trichomes, found in highest concentration on the flowers and those with the greatest cannabinoid content, appearing somewhat like a tall mushroom, with a long stem and a large, rounded head – the iconic image of a trichome.
As the flowers mature, the trichomes will change colour, starting out transparent, passing through a milky-white stage nearing maturity and going on to become amber coloured when fully mature. Different growers will harvest their flowers depending on personal taste and the effect they’re looking for, but on our blog you can read a useful guide to harvesting according to trichome ripeness, which will help you to bring your crop down at the optimum moment.
Hopefully after reading this you’re now a bit more familiar with the anatomy of the cannabis plant and will become a better grower as a result. Knowledge is power!
The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.
Breaking Down the Cannabis Plant
We wanted to start our blog with some Cannabis plant basics. In this series, we hope to explain all the pertinent Cannabis plant facts at-a-glance. There is so much information and so much science out there and we aim to guide you through it all. In today’s information age, it’s hard to know where to start with educating yourself on the Cannabis plant. With our collective decades of experience, we decided it’s best to start from the beginning; the plant itself.
Cannabis is like every other plant. Its growth cycle starts from a seed, grows and matures over time, and ultimately flowers and then repeats the cycle until it dies. The flowers are the most desirable part of the growth process and it is no different for Cannabis. Once a cannabis plant flowers, those flowers produce resin glands that contain cannabinoids and terpenes. These flowers are what is being harvested and ultimately used or processed into different medicine and other consumable items. What we call flower, pop culture calls “bud,” “weed,” “ganja,” “pot,” etc.
Parts Of the Cannabis Plant
The flowers contain the CBD and terpenes that cause you to get high and give people a number of other benefits, interacting with the endocannabinoid system. Flowers only grow on the female plants. This is what is dried out and ground before being smoked.
The cola on the cannabis plant is a cluster of buds growing closely together, almost in a bunch. Small colas can be found up and down the low branches, but the main cola almost always sits at the top of the marijuana plant.
The pistil is where the reproductive parts of the flower sit. They contain a lot of thin strands that look a bit like hair, called stigmas. They collect the pollen that is carried from male plants. The stigmas that can be found within are white when the plant is young but eventually turn yellow through the weed plant stages.
The pistil is all about the reproductive system of marijuana.
The bracts are what can be found around the female’s reproductive area. They are green, with leaves in a sort of “tear shape”. They have a number of resin glands, that actually hold the highest number of cannabinoids within the marijuana plant.
Inside the bracts, on the female cannabis plant, is the calyx. This is a see-through layer that protects the ovule. You can’t see it with the naked eye.
Trichomes are small but form an important part of marijuana anatomy. They make a crystal-like covering for the buds of the cannabis. Trichomes actually come from glands on the leaves, stems, and calyx of the female or male cannabis plant.
Trichomes protect the plant from anything in the wild that could harm them. They secrete terpenes and both CBD and THC.
The node is where a branch grows from the stem of the cannabis plant. Or where one branch stems off and creates another. Some nodes contain buds, but not all of them.
The nodes play an important role in the sexing of a cannabis plant and telling a male cannabis plant from a female cannabis plant. More on that later.
If you see clothing or accessories with a cannabis leaf on them as decoration, this will be from the fan leaves. They actually just capture light and don’t have a lot of resin within them. On a cannabis Sativa plant, the leaves tend to be further apart and more sparse.
Sugar leaves are where the resin is usually held. They’re small leaves where the buds form, and you can use them in a variety of cannabis products including pre-rolls, or to make THC and CBD extracts.
This is a term you’re probably familiar with. The stem is the same part of a cannabis plant as any other plant, and it gives structure and stability to the other parts of the marijuana plant.
The top of the stem can be cut off to encourage weed plant stages where the marijuana plant grows more branches and more buds.
How to tell male from female cannabis plants
To check the sex of a cannabis plant, you need some understanding of marijuana anatomy.
You should check in between the nodes. These are the parts of the marijuana plant where the branches spring off from a stem. On male plants, pollen sacs can be found here. On a female, stigma develops so they can catch the pollen.
You can see pre-flowers from around the fourth week of cannabis growth. In week six, it should definitely be clear what sex the plants are.
For a male marijuana plant, you’ll find small sacs growing. On females, you will find bracts on the cannabis plants. This is where the hairs that catch pollen will eventually start to grow.
How to propagate cannabis plants
There are numerous ways to propagate cannabis plants so that more will grow in the future.
Cloning is not as daunting as it sounds. You don’t have to do it in the lab. This is where you take a cutting from a cannabis Indica or cannabis Sativa plant and put it in the ideal growing conditions in soil or hydroponics.
It’s relatively simple and reliable. It also means that you know what type of cannabis plant is going to grow, and you will have taken cuttings from a healthy “mother”. Cannabis clones are going to take all you liked about the mother plant and create another generation that grows in the same way.
Clones are delicate, and you need to get good at understanding an active vegetating cannabis plant so that you can make a clone, there is definitely a skill involved in picking the cutting, making the cutting itself, and replanting it. You probably won’t get it 100% right the first time around.
Seeds don’t need you to grow from an initial plant, you can buy seeds and plant them just like you would any other plant, fruit, or vegetable. It takes a little longer for them to grow this way.
Seeds don’t always germinate, so there is a real art to growing your own marijuana using seeds.
One good thing about seeds is the fact that they haven’t been exposed to diseases or a bad growing environment. You can also buy feminized seeds if you want, which guarantee a certain percentage of female cannabis plants.
Another positive thing about seeds is that they can easily be shipped and transported, and you can buy a number of varieties of cannabis. You might even be able to germinate your own strands.
Whether you choose cannabis clones or growing from seeds, it doesn’t matter, as long as you make a point of becoming good at it. A lot of manufacturers prefer to use clones as it gives a much more consistent result, and allows you to know the properties of the plant that will grow.