Stages of Growth
Cannabis transitions through several developmental stages of growth, just like we do. Cannabis requires different inputs and climate conditions during different growth stages. This plant will grow like a weed when these requirements are met, but success is not guaranteed. Understanding the plant’s needs during these growth stages will help you get the best performance from your plants.
Cannabis Growth Stages:
1) Seedling Stage
The seedling stage begins when the first seed leaves emerge and begin to photosynthesize.
The seedling growth stage usually lasts for 15 to 20 days as the young plant becomes more established. The second set of leaves to emerge are also single-bladed, but have serrate edges, and look like cannabis leaves. This is the first true leaf set. As soon as the first true leaf set has emerged, the plant will require sufficient light to avoid elongation, or stretching. Subsequent leaf sets occur in pairs, on opposite sides of the stem and leaf blades will typically increase to 3, 5, and then 7 blades as the plant matures.
The intersection of each leaf stem (petiole) with the main stem is known as a node. A new shoot will emerge from each node as the plant matures. Seedlings are usually either germinated in small 4” cups or germinated in root plugs before being transplanted into small.
2) Vegetative Growth
Once a cannabis plant has a well-established root system, and 4-6 nodes of growth it enters the vegetative growth stage.
The ideal relative humidity at this stage is 65-70%. The plant will continue to elongate and develop mature 5 to 7 blade leaf sets.
Seedlings are usually potted up into a 1-gallon pot, or directly into their final pot for the vegetative growth stage. This allows for root expansion to support continued growth of foliage. As cannabis plants mature, secondary shoots at each node of growth will begin to develop leaf sets of increasing complexity.
If conditions are favorable, your cannabis plants will grow like a weed during the veg stage. When plants are well rooted, and growing vigorously, training and pruning techniques will help shape the plant for future production without compromising growth.
Several training techniques are commonly applied to cannabis plants to increase the number of colas, or top flowers, while decreasing overall height of the plant. These techniques include low stress bending, and high stress interventions like topping. For more information on training techniques see out article titled Training Cannabis Plants.
Sexual Maturity
Most Cannabis plants will become developmentally mature when they reach 14”-20” in height, or 8 to 10 nodes of growth. At this stage the leaves and shoots at each node will begin to alternate, rather than occurring opposite each other. Plants may begin to pre-flower, developing reproductive organs that allow determination of their sex.
Cannabis plants are dioecious, meaning that male and female reproductive organs occur on different plants. This is fortunate for us, as it allows us to select the desirable female plants, while eliminating male plants before they can seed our crop.
Feminized Seed
There are a few reliable ways to ensure that our plants are all female. Hi quality feminized or all female, seeds are now widely available for purchase. These seeds can save a lot of time and resources for cultivators regardless of size of their garden. When sourced from a reputable breeder, the plants grown from feminized seed will be over 99% female, with a very small percentage of hermie or intersex plants.
Genetic testing
There are also genetic tests available to determine if a plant is male or female. These cost about 10 dollars per test and can very accurately identify plant sex through genetic analysis.
For home growers, facing strict plant counts, it is very helpful to quickly determine the sex of your plants, and be assured of complete accuracy. This process usually involves removing a cotyledon from a seedling, compressing it with blotter paper, and mailing the sample to a lab.
The resulting sample is legal to mail anywhere in the world, as no cannabinoids are present. In most cases, genetic testing costs less than growing plants until they are mature enough for visual identification.
Visual Identification
The traditional way to separate male plants from female is through visual identification during the pre-flower stage. These pre-flowers will form next to the stipule at the base of each node.
Visual identification is straightforward, but with some strains the pre-flowers may not be evident until after flowering has been induced. This is inconvenient and can result in gaps in flowering canopies, and accidental seeding if growers are not attentive.
3) Early Flowering
Cannabis plants are either autoflower or photoperiod plants.
Autoflowering plants will enter the early flowering stage after 10-20 days of vegetative growth regardless of the light cycle these plants are exposed to.
Photoperiod plants will begin to flower when they receive more than 10-11 hours of uninterrupted darkness during each 24-hour period.
Plants begin to elongate, or stretch about 7 days after entering flower, and stop growing taller after about 3 weeks. The early flowering stage is really a hyper vegetative period. At this point the plant has been trained and a trellis is usually installed to support the large cannabis flowers that are just beginning to form. Lots of organic Nitrogen, and plentiful water is necessary to sustain vigorous growth.
Ideal climate conditions for this stage of growth include 55%-70% relative humidity and temperatures of 72-84 F (22-29C). For indoor gardens, light intensity is slowly increased to make up for the reduction in light hours to a 12hour photoperiod.
As flowering progresses, the plant will stop vertical growth, and begin to form much simpler leaf sets. The reproductive organs, or pistils, will multiply, and cluster into small round buds.
There should be a strong focus on pest management during the early flower period. Reduction in pest populations to an absolute minimum during early flower will help to preserve crop quality during later flowering stages when pest pressures are higher, and treatments are more limited.
4) Mid Flower Stage
Plants will stop growing vertically and making new leaves about 20 days after flowering begins. The plant’s development will shift to flower expansion during the mid flowering stage. Flower expansion will continue until about 35 days after initiation. Relative humidity should be reduced to 50-60% to limit the risk of fungal disease. At this stage, plants are at the peak of their reproductive potential.
Pistils have congregated to form large flower sets, or colas.
Each pistil is a reproductive organ. Their collective sexual frustration, due to lack of pollen fertilization, results in the profuse formation of psychoactive cannabinoids. These cannabinoids are synthesized within glandular trichomes.
Other substances, including flavonoids, esters, and terpenoids are also synthesized by the plant during the peak flowering phase. The presence of some of these compounds, particularly monoterpenes, is very evident during this period due to the smell of success that emanates from the crop.
As the flowers expand, some of the older leaves will start to yellow, and fall off. These should be removed as soon as possible. Some of the fungal diseases that affect cannabis are saprophytes and will infect dying plant material.
During early and mid flower, it is often helpful to selectively remove fan leaves. Fan leaves are removed to allow light to penetrate the canopy and directly illuminate flower sites, and to enable air to flow through the canopy. Airflow is important for climate equalization, to prevent disease, and promote plant health.
5) Late Flower Stage
The late flowering stage is when the bulk of psychoactive cannabinoids are synthesized. Between 20 and 30 percent of the dried flower weight is added during the final ripening phase. Humidity should be reduced to 50-60% to prevent bud rot from establishing in the large flowers. Temperatures should be reduced to a maximum of 80 degrees Fahrenheit (27 C)
Nighttime temperatures are also often reduced during this growth stage. The reduction in temperature during late flower serves several purposes.
- When the humidity has been reduced, lowering the temperature helps the plant to transpire more efficiently due to a reduction in the Vapor Pressure Deficit (VPD).
- Lower temperature can also help to manage the reproductive cycle of pests, including the three spotted spider mite, which thrives in hot-dry conditions.
- Lower nighttime temperatures can also increase the purple coloration in cannabis flowers. Cannabis plants, like many other plants, will produce a purple pigment known as anthocyanin when exposed to temperature extremes.
Anthocyanin absorbs light energy as heat and helps to protect plants against both hot and cold temperatures.
Cannabis flowers change appearance as the white hairs or stigmas emerging from the pistils dry up and lose their ability to become pollinated and form seed. This final stage of plant life is also known as senescence. Many leaves will begin to yellow and die at this stage, and the plant is at its most vulnerable to pest attack.
Harvest Timing
The Three Rules for Harvesting Marijuana at the Right Time
Trichomes and pistils are the best visual indicators of when to harvest. Both change color or shape as the plant reaches maturity, making them easy references. For those with laboratory equipment available, chemical testing is a reliable method also.
- Trichomes are the mushroom-shaped resin glands found on the flower and nearby leaves.
- Pistils (or stigma) are the hairs coming from the flower’s calyxes.
Checking for THC via the Trichome Method
Trichomes slowly change color from clear to milky-white as the plant matures. Opaque milky-colored trichomes indicate that resin production has peaked, and secondary metabolites like THC, CBD, and terpenes are at their maximum. Yet not all of the trichomes will turn cloudy at the same time; it is a gradual process.
So when most of the trichomes have become opaque, a few will have already transitioned into amber or brown hues. Amber trichomes indicate ripeness has passed and the medicinal compounds are degrading.
Guideline #1: Harvest marijuana when more than half of the trichomes have turned a cloudy, milky color.
Most cultivators who use the Trichome Method for harvesting take down their plants when more than half of the trichomes have turned from clear to cloudy and just a few are amber. If most of the trichomes are amber, the plant is past its peak.
Checking for THC via the Pistil Method
Consumers often refer to pistils as “hairs” — and with good reason. The slender, white pistils point outward from the flower’s calyx, attempting to receive pollen and produce seeds.
When the plant approaches maturity, the pistils change color and take on a brown or orange hue. This is a sign that the biological functions of the plant have slowed and it is no longer seeking pollen for seed production.
Guideline #2: Harvest marijuana when 70% of the pistils have turned brown or orange.
Most cultivators who base their harvest date on the Pistil Method take down their plants when 70% of the pistils have changed color and curled inward. If 90% of the pistils are brown/orange, the plant is past its peak.
Checking for THC with Laboratory Testing
Cultivators with access to chemical testing equipment have more control. By tracking their crop’s cannabinoid concentrations, they can pinpoint when THC and CBD are at their peak.
Final THC concentrations are unpredictable. So, when chemical testing, cultivators use a different strategy: they track CBG.
Guideline #3: Harvest marijuana when CBG levels drop close to zero.
When CBG levels approach zero, they know that all of the CBG has converted into more desirable cannabinoids, namely THC and CBD.
Growing your own cannabis is not rocket science, but your chances of success are much higher if you pay attention to your plants needs during the various development stages.
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The information presented on 420GrowHelp.com should not be regarded as financial, legal, or medical advice. It is your responsibility to familiarize yourself with and abide by the local laws and regulations pertaining to the cultivation, possession, and use of cannabis. Decisions regarding cannabis cultivation should be made in consultation with a lawyer or qualified legal advisor, while decisions regarding cannabis use should be made in consultation with a doctor or medical professional.