In this tutorial, we walk you through everything you need to know and do to grow cannabis seedlings in coco coir: pots, light, fertilizers, watering & more In general, the smaller the seed, the shallower you should sow. Tiny seeds can even be scattered on the surface of soil to germinate. Sowing too deep can… A step-by-step guide for successful cannabis germination grounded in science. Reviews strategies for germinating cannabis seeds and offers tips for success.
How To Grow Cannabis Seedlings in Coco Coir
The seedling stage is one of the most sensitive periods of a plant’s life. If managed well, seedlings develop into strong young plants that go on to be solid producers. However, if managed poorly, the plant can become stunted and never live up to its potential. Caring for seedlings in coco coir can be tricky, but we have you covered. In this tutorial, we walk you through everything you need to know and do to grow cannabis seedlings in coco coir. We cover how to prepare coco for seedlings, the best containers for seedlings in coco, relative humidity for cannabis seedlings, temperature for cannabis seedlings, light for cannabis seedlings, fertilizers for cannabis seedlings, how to water seedlings in coco coir, and how to treat seedlings with calcium deficiency.
This tutorial covers the roughly two-week period of the seedling stage. The seedling stage starts when the cotyledons (first round leaves) open, usually around 3-4 days after the seed gets wet. The seedling stage runs until the plant has three true nodes (sets of serrated leaves). Hence, this tutorial covers roughly days 3-15 from seed. For those crucial first 3 days, be sure to see our tutorial “Germinating Cannabis Seeds – a Step-by-Step Guide”.
As the plants start maturing during the seedling stage, it is time to work your way through a transplant strategy. We recommend that you always use a transplant regime and never start seedlings in final containers. For simple instructions and our explanation, be sure to see our tutorial, “Transplanting Cannabis Plants: Why, When & How”.
You will eventually get to final containers, so be sure to read our recommendations in “Pot Size and Type: The Best Containers for Cannabis in Coco” (Coming Soon). The end of the seedling stage is also when you should think about training your plants, so be sure to read our article, “Why You Should Train Cannabis Plants” and see our training tutorials.
How to Grow Cannabis Seedlings in Coco Coir
Coco Coir, CalMag and Seedlings
Before you use coco, it should be properly rinsed, buffered and mixed with perlite. Be sure to see our video and tutorial for “How to Prepare and Buffer Coco Coir”. The buffering process is crucial to prepare the coco for plants, and especially seedlings.
As I explain in the article, “Why You Need Cal/Mag in Coco”, the coco itself has cation exchange sites that need to be filled with calcium or magnesium. Buffering the coco allows you to satisfy the majority of the cation exchange sites. However, during the grow, more cation exchange sites are continuously exposed, which require additional CalMag. The coco will take its share of the calcium and magnesium before the plant has a chance, so if you do not provide enough, the plant will suffer.
Calcium and magnesium deficiencies are common problems with plants grown in coco. It is especially difficult to deal with CalMag problems during the seedling stage. This is because the coco is taking the Ca and Mg from the nutrient solution. However, you cannot simply increase the dose. You are limited in the amount of CalMag that you can provide to seedlings because they cannot tolerate a solution with high Electrical Conductivity (EC). CalMag has a strong impact on EC so when seedlings do suffer Ca or Mg deficiencies, they can be tough to correct. If you do encounter problems with Ca or Mg deficiency during the seedling stage, we have suggestions for you below. However, it is best to avoid the problems in the first place by properly preparing your coco.
How to Prepare Coco for Seedlings
Buffering with a strong dose of CalMag prior to using the coco allows you to provide relatively little CalMag during the seedling stage of the grow. However, buffering solutions themselves have a high EC, and seedlings could be burned if they are placed in coco fresh from the buffering process. Therefore, it is important to reduce the residual EC in the coco before transplanting the seedlings.
When I begin a grow, I prepare and buffer enough coco for the final containers. I keep the bulk of the coco/perlite moist with CalMag Water in fabric pots until I need it. When it comes time to place seedlings into coco, I fill the seedling container with coco/perlite and then flush it by pouring pure water with a pH of 6.5 though the container until the run-off is less than EC 100 (0.1). This flush is important because otherwise the residual high EC from the buffering process could burn your sensitive seedlings.
Containers for Seedlings in Coco
We recommend growing sprouts first in a Rapid Rooter or Jiffy Pellet before transferring to coco. These peat-based media provide a more stable buffer for germinating seeds and sprouts. Be sure to see our tutorial, “Germinating Cannabis Seeds – a Step-by-Step Guide”.
When the root of the sprout grows through the Rapid Rooter or Jiffy Pellet, the little plant should be transplanted into the first container, where it will live out its seedling days. We advise strongly against placing small plants into large final containers. As I explain in our article, “Transplanting Cannabis Plants: Why, When & How”, there are significant benefits to starting plants in small containers.
When the root emerges, we recommend placing the plants into either fabric seedling bags or solo cups with prepared coco. The seedling bags create an ideal environment for young roots, however the solo cups are somewhat easier to transplant out of at the end of the seedling stage. If you use solo cups, be sure to cut numerous holes in the bottom of the cup to allow drainage.
Transplanting out of seedling containers can be tricky whether you use fabric seedling bags or plastic solo cups. For complete instructions and photos of the process be sure to see “Transplanting Cannabis Plants: Why, When & How”.
How to grow plants from seeds: step by step
In general, the smaller the seed, the shallower you should sow. Tiny seeds can even be scattered on the surface of soil to germinate.
Sowing too deep can prevent germination, causing seeds to go dormant.
Step one: sowing
Thoroughly clean reused containers to avoid contamination from diseases or pests.
Even when growing indoors, follow planting timelines – healthy seedlings can still be killed by low temperatures.
- Choose and weed the sowing area, or fill a container with growing medium
- Water the area well until damp throughout
- Scatter or sow in drills when sowing outside; sow individually in small containers, or spaced evenly apart, in large ones
- Cover seeds with a light layer of growing medium or leave on the surface
- Water outside seeds lightly with a fine watering can head to avoid displacement. Cover inside seeds with a clear material, like glass, to seal in moisture and allow light through.
Sheltering indoors allows for sowing earlier in the season. Heated greenhouses or well-lit spacious rooms make it possible for some to be sown as early as January.
Most are sown in February or March for planting out in May or June, after frost.
A clear cover over germinating seeds should retain moisture and warmth. If the soil seems dry, water from the bottom via a drip tray.
Watering from above can dislodge seeds and compact soil. Watering from below preserves the soil structure and encourages roots to grow.
Before the growing season starts, cultivate the soil by layering compost or organic matter on top. This produces healthy, nutrient-rich soil with good aeration and drainage.
Soil type may affect when to sow: light soil warms faster; heavy, waterlogged soil can take longer.
Some plants, such as lettuce, cucumbers, melons and sunflowers, fare better when sown outdoors after the last frost, rather than being transplanted.
Horticultural fleece, or similar removable insulation, can protect germinating seeds without stifling growth.
Sowing in drills helps to arrange flowers and vegetables. Dig a shallow trench in the desired pattern, space seeds accordingly at the bottom, cover with soil and lightly pat down.
‘Scattering’ creates a wilder look, suited to wildflowers or cottage gardens. Be aware that thinning out may be required after germination.
Step two: germination
Germination usually takes three to six weeks. However, it can take up to 15 weeks for some plants.
The first true leaves indicate that germination is complete. Many plants grow a set of small, light leaves called cotyledon before their first true leaves.
Once indoor seeds have germinated, remove the clear cover to allow airflow. Move the seedlings to a location where they will receive lots of direct sunlight, and turn regularly to promote even growth.
Keep the soil damp, without flooding new plants, and ensure soil temperature remains warm and steady.
You’ll need to monitor outdoor plants in case they need to be thinned out (to reduce competition) and for problems caused by bad weather or pests.
Step three: planting out
Transplanting smaller seedlings
Smaller seeds can be ‘pricked out’ from shallow starter pots before full germination, to provide room for growth. Loosen soil around the roots with a blunt stick, and then lift gently by the first set of true leaves. Keep as much soil around the roots as possible to prevent transplant shock.
Once the roots of larger seedlings have filled their containers, and smaller seedlings have germinated fully, they’re ready for planting out.
If you are intending to grow plants indoors, they can be transplanted into containers large enough for healthy adult root systems and grown from there.
Plants heading outside will need to undergo hardening off.
Move plants outside in their containers for increasing amounts of time, to acclimatise them to a less controlled environment.
At this stage, you should water less frequently, but in higher volumes. Regular, light watering encourages the formation of weaker root systems. Watering from the bottom, or flooding a couple times a week, encourages deeper, stronger roots.
Step four: maintenance and aftercare
Once seeds have grown into adult plants, they need less attention. However, they still require monitoring for signs of deficiency.
Pruning, controlling competition from surrounding plants, and preparing for adverse weather can prolong the life of your plants. Move containers or pot plants to shelter or indoors during storms or cold snaps.
Mulch or chips can be used for insulation once plants have germinated. This protects against extreme temperature changes or rainfall.
Coco coir for healthy seed growth
Coco dots are perfect for starting seeds. Containing all the benefits of coco coir, they’re water retentive, naturally sterile, and offer excellent drainage and aeration.
Once the seeds have germinated, coco dots can be transplanted with seedlings directly into pots or beds.
Coco coir’s fine structure makes germination easier on smaller plants. Superior aeration and drainage mean enough water is provided while avoiding rot.
At Coco & Coir, we take pride in supplying hard-working gardeners with the right growing mediums for successful planting projects. Our online store contains a range of coco coir products to get you started, including coco dots and coco chips.
In addition, our extensive blog archive contains a trove of hints and tips to aid growing success.
Germinating Cannabis Seeds – A Step by Step Guide
Germinating cannabis seeds is one of the most exciting parts of the whole grow. It is almost magical to summon new life from a dormant seed; however, it can be very frustrating when things don’t go well. In this article, I explain how to germinate cannabis seeds successfully. I begin by reviewing the science of germinating cannabis seeds. I then describe several common cannabis germination strategies and share some cannabis germination tips and tricks. At the end of the article, I provide my step-by-step guide to germinating cannabis seeds. Be sure to watch my Germination Tutorial on YouTube!
Germination will always be exciting, but it does not need to be intimidating. There are many ways to germinate cannabis seeds successfully. Understanding the science and the shifting needs of the developing plant will allow you to choose the germination strategy that is right for you.
The Science of Germinating Cannabis Seeds
Cannabis seeds are among the easier seeds to germinate. They are large dicotyledon seeds that store a reasonable amount of energy for early life. Furthermore, cannabis seeds do not have any significant seed dormancy factors to overcome. If they are viable seeds they will germinate easily when exposed to the correct conditions.
Seeds become Sprouts During Germination
This may sound obvious, but it is important to consider because seeds and sprouts are different. When the cannabis seed is still a seed, it is resilient and does not depend on ideal conditions to survive. However, sprouts are different. As soon as the seed cracks open and exposes the radicle (tip of the root) it becomes a sprout. As a sprout, it becomes much more sensitive to external conditions. Whereas the seed only needs warmth and moisture to germinate; the radicle on a sprout needs warmth, moisture, oxygen, and darkness to survive and grow.
Germination Stage 1: Imbibition
The seed’s journey to planthood begins by getting wet which starts the process of imbibition. Imbibition is similar to rehydration. When wet, the testa or seed coat of cannabis seeds imbibe water which causes them to swell and soften. The force of water entering the cells in the testa physically ruptures the seed coat and allows the radicle (root tip) to escape. The imbibition of water also activates the metabolic activity within the seed protoplasm.
Warmth is Required for Metabolic Activity
The metabolic activity within the seed will only activate if the temperature is in the appropriate range. Like other seeds, cannabis seeds will not successfully germinate if the temperature is too low or too high. Room temperature is warm enough to allow germination, but warmer temperatures enable more metabolic activity and faster germination. The ideal temperature range to germinate cannabis seeds is 80-86 F (27-30 C).
Germination Stage 2: Respiration
Seeds carry stored energy to help power metabolic activity and growth until the plant can begin photosynthesis. However, just like humans and other animals, plants must engage in respiration in order to convert that stored energy into active energy that the plant can use. During the earliest stages of metabolic activity as the seed awakens from dormancy, the respiration is anaerobic or without oxygen. However, the sprout needs to quickly begin using oxygen in aerobic respiration to continue to survive and grow.
As metabolic activity resumes, the sprout will begin to grow. Cannabis seeds store most of their energy in their cotyledons in the form of starches and proteins. The plant uses energy from aerobic respiration to digest these starches and proteins into simple sugars and amino acids, which it mobilizes to grow the radicle (root tip) and hypocotyl (stem).
Cannabis Sprouts need access to both water and air
Seeds can be completely submerged in water during the first part of imbibition. However, if they are completely submerged after the radicle is exposed then the sprout will die from lack of oxygen. As soon as the seed cracks open and exposes the radicle it needs to have access to oxygen for aerobic respiration. This means that it needs some contact with air. However, it also needs continuous contact with water. To achieve the best results in the sprout and seedling stages it is best to use a grow media that will trap both air and water. As I explain below, paper towels work well for this during the early sprout stage and germination media like Jiffy Pellets or Rockwool cubes are perfect for young seedlings.
Germination Stage 3: Orientation
At this stage of germination, the plant must orient itself to grow properly. The radicle must push down into the soil or media and the hypocotyl must push the cotyledons (first leaves) up out of the soil or media. Both gravity and light help orient the plant to grow in the proper direction.
Apply Light but Keep the Radicle in the Dark
Cannabis seeds do not require darkness to germinate. However, the radicle is sensitive to light. Bright light will stunt the radicle and can lead to a failed germination. When seeds are germinated in paper towels it is best to keep the sprout in total darkness until the radicle is about half an inch long (about 1.25cm). However, as the cotyledons emerge from the seed casing, they will be looking for light to indicate the direction they need to grow. Therefore, when the radicle is longer than half an inch it should be placed in media which will protect it from light. Once the radicle is safely in the media, light should be applied to the top of the media to signal the direction of growth for the cotyledons.
Germination Stage 4: Photosynthesis
During the germination stage the plant relies exclusively on stored energy from the seed. This energy is limited, so the plant must quickly begin producing its own energy through photosynthesis. The young plant works to establish its radicle in the media and push the cotyledons up into the light to begin photosynthesis. Once the cotyledons open and receive light, the plant will begin photosynthesis. At this point, germination is complete, and the plant can start producing its own sugars, starches, proteins and fats.
Nutrients for Germinating Cannabis Seeds
The nutrients and supplements that we provide to our plants are not their food. Nutrients and supplements support photosynthesis. Therefore, they are not needed until the plant has begun photosynthesizing. Indeed, adding nutrients to the water used for imbibition can actually inhibit germination. It is best to use plain water at a neutral pH (7.0) to imbibe the seeds.
Once the cotyledons are open, the plant can use very small doses of nutrients. However, it is easy to overdo it and burn the plant. When and how to begin fertilization depends largely on the media that you are growing in. If you are growing in coco or other inert and unamended media, be sure to read “How to grow cannabis seedlings in coco coir”.
Cannabis Germination Strategies
There are many viable ways to germinate cannabis seeds. Different germination strategies may be more suitable for different growers. Therefore, before explaining my step-by-step guide to germinating cannabis seeds, I will review some of the more popular germination strategies.
Many growers begin germination by soaking seeds in water. This allows for faster imbibition of the seed because it is surrounded by water. It is a safe strategy to follow as long as you remove the seeds from the water before the seed actually cracks open. If you soak seeds, you should use plain (low EC) water with a neutral pH (7.0). Filtered or distilled water is best.
The Paper Towel Method
This seems like a make-shift hack, but wet paper towels provide an excellent air/water ratio for germinating seeds. They also allow you to precisely control the temperature of the seed/sprout during germination. As a result, using paper towels can speed the germination process considerably.
The paper towels should be fully saturated with water, but not dripping wet. I like to fold the paper towel so that there are two layers below and above the seed. You can then place the paper towels in an air-tight container to prevent them from drying out. I use pyrex containers. If you use a plastic bag, just make sure that you trap some air in the bag (don’t squeeze all the air out). The radicle does need some air, but there will be plenty, even in a sealed container. Place the sealed container someplace warm and cover it to protect the radicle from light.
The main drawback to the paper towel method is that it is possible to damage the young sprout when you transfer it to media. There are some easy practices to mitigate this risk. First, use cheap, single-ply paper towels. This prevents the radicle from growing between the plies. Second, place only one seed on each paper towel. This allows you to pick up the whole paper towel and avoid touching the sprout when you transplant to media. Finally, don’t keep the seeds in paper towels for too long. Once the root has grown to about 0.5in or 1.25cm, it is time to transplant it to media.