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Seeds, germination and seedlings

This paper shows how to select a seed, how to germinate it, and how to keep the seedling in good condition. It also gives a definition of a seed. In the first three weeks, the seedling is very weak.

Basic9 figures9 sources~14 min to read

In this paper

01 Purpose and scope 02 Definitions 03 Evidence and limitations 04 Seed anatomy and quality check 05 Cannabis seed types 06 Germination methods 07 Germination conditions and time sequence 08 Seedling procedures in the first two to three weeks 09 Troubleshooting 10 Expected results and limitations 11 References

Start here

Purpose and scope

This paper is for a new grower. It shows the procedure from a dry cannabis seed to a seedling in good condition after two to three weeks. The paper gives a definition of each term where the term first occurs.

A seed is a small plant in a protective shell. The plant has no growth until the conditions are correct. Germination is the start of growth of the seed. A seedling is a small plant in the first weeks after germination.

Most of the errors that kill a plant occur in the first 21 days. Thus, when you do these first stages correctly, the other stages of cultivation are much easier. Read this paper before you get a seed and before you plant it.

Figure 1. The figure shows all the stages in this paper. A dry seed absorbs water, and the taproot comes out of the seed. You plant the seed, and the seed leaves open. By approximately week three, the seedling is strong.

Information in this paper

How to select a seed, how to germinate it, and how to keep the seedling in good condition until approximately day 21
Germination is the start of growth of a seed. A seedling is a plant in the stage when it is weakest.
Most problems of a new grower have their cause in the first three weeks (rot, seeds that do not germinate, and growth that stops)
Each term has an easy definition where the term first occurs

Terms

Definitions

This section gives the terms that the other sections of this paper use. It is not necessary to know the terms at this time, because each term occurs again in the other sections.

Taproot (radicle)The first white root. It comes out of the seed and becomes longer in the down direction. The root is straight. The taproot shows that the seed germinated.

CotyledonsThe two round ‘seed leaves’ that come first. They supply the plant with the nutrients of the seed, until the true leaves start to supply the plant.

True leavesThe usual cannabis leaves, with a serrated edge. They come after the cotyledons. When they come, the growth of the plant starts.

Seed coatThe outer shell of the seed. It is hard and protective.

EmbryoThe small plant in the seed. Its folded parts are a taproot, two cotyledons, and a small shoot. The plant has no growth until germination.

Germination rateThe percentage of seeds in a batch that germinate.

ViableA viable seed can germinate. A seed that is not viable cannot germinate. No task that you do will change this.

Damping-offA fungal disease. It makes the seedling rot at the soil surface, and the seedling falls. No other problem kills more seedlings.

A short glossary. Use this table again when you read the sections that follow.
Term	Definition
Taproot / radicle	The first root of the seed. It becomes longer in the down direction.
Cotyledons	The two round ‘seed leaves’ of the embryo
True leaves	The serrated cannabis leaves that come after the cotyledons
Seed coat	The protective outer shell of the seed
Embryo	The small plant in the seed
Germination rate	The percentage of seeds that germinate
Viable	A seed that can germinate
Damping-off	Fungal rot at the bottom of the seedling stem

Diagram. The sequence of germination: a viable seed absorbs water. The radicle comes out of the seed and becomes the taproot. The cotyledons move up. Then the true leaves start.

Diagram. The parts of the seed: the seed coat gives protection, the endosperm gives nutrients, and the embryo (the radicle and the cotyledons) becomes the plant.

Quality of the information

Evidence and limitations

Three types of information

We want each paper to be correct. Thus we examine each paper for information that is not solid. This information comes from the view of one grower, from a small number of sources, or from grower methods that have no controlled test. We identify this information, and we do not show it as solid.

Frequently there is no paper for the decision that you must make. Then we use the reports of other growers and the methods that work in the rooms that we know. This information can help you, but it is not the result of a laboratory test. Use the methods that work for your plants, for your room and for your meters. If a table does not agree with your crop, use the data from your crop and record the difference.

Solid

Tests of plants, specifications or many sources that agree show that the information is correct

Water and a warm temperature are necessary for seeds. Damping-off occurs because of conditions that are too wet and have no air movement.
Feminized seed is the result of XX×XX induction with STS, colloidal silver or an equivalent method. The seed does not give 100% protection from hermaphrodites.
The length of the night controls flowering in photoperiod plants. Autoflower plants make flowers mostly because of their age and genetics.

Grower method

Many growers use this method in their rooms. Start with it, then change it for your room.

A germination temperature range of 21 to 25 °C, and slow PPFD ramps for seedlings.
Use a humidity dome and a high RH at the start. Then decrease the humidity when the roots become longer.
Visual checks of seed quality (color and firmness) as a first selection, and not as a laboratory test of viability.

Weak

The view of one grower, a small number of sources, one test, or a method that works in one room

One germination percentage for all seed lots. The age of the batch and the storage have the largest effect.
Very high germination rates for the paper towel method. The method is less important than the quality of the seed and the control of moisture.

If you find an error, make a report. We will correct it. Make the report on GitHub, with the name of the paper and the information that is incorrect. If you have a source, include it: Make a report of an accuracy problem. The regulations, labels and licenses of your area always override each procedure in these papers. The label weak in a paper shows the points where the risk of an error is highest.

Primary information 1

Seed anatomy and quality check

A cannabis seed contains a small plant with all its parts. The plant has no growth until germination. A hard seed coat gives protection to the embryo. The embryo has a taproot, two cotyledons, and a small shoot. The seed also contains nutrients. The plant uses these nutrients in the first days of growth, before the true leaves supply nutrients to the plant.

Figure 2. The figure shows the inner parts of a seed. The seed coat gives protection to the embryo. The embryo has the taproot, the cotyledons, and the shoot. The seed contains a small quantity of nutrients around the embryo.

You can see some signs of quality. Mature, viable seeds are hard and dark brown. They frequently have stripes or marks of a different color (‘tiger stripes’). They do not break when you apply small pressure with your fingers. Pale white, yellow, or light-green seeds are usually immature, because the grower harvested them before they were mature. These seeds frequently have a low germination rate, or they make weak plants.^[1]

New seeds that you keep cool, dark, and dry stay viable for years. But the germination rate decreases when the age of the seeds increases. In this time, degradation of the oils in the seeds occurs.^[2] A sealed container in a refrigerator is a good storage area for seeds that you do not use at this time.

Examine the seed and touch it before you start germination. This check is short.
Check	Good (viable) seed	Bad (usually not viable)
Color	Dark brown, frequently with marks of a different color	White, yellow, or light green
Surface	Stripes (‘tiger stripes’)	No stripes, matt surface
Hardness	Hard. The seed does not become flat.	Soft. The seed changes shape when you apply pressure.
Test with the fingers	Keeps its shape	Breaks

Pale seeds can be viable

Pale seeds that are immature can germinate, but frequently they make plants that are weaker and of lower quality. If you can select, plant the dark, hard seeds with stripes first.

Primary information 2

Cannabis seed types

There are three types of seed. Your selection of a type has a large effect on your cultivation. Regular seeds make approximately half male plants and half female plants. Only female plants make the flower (the ‘bud’) that most growers want. Thus growers usually remove the male plants.

Breeders make feminized seeds. These seeds give almost only female plants. Thus it is not necessary to find male plants and remove them. This prevents work that is not necessary. Breeders cause a female plant to make pollen with a treatment such as colloidal silver. The seeds that this pollen makes have only female genetics.^[4]^[5]

Autoflower seeds have the genetics of Cannabis ruderalis. These genetics make the plant start the flowering stage after approximately 2-4 weeks. The light cycle does not change this. The time from germination to harvest is approximately 60-90 days.^[6] Photoperiod plants (regular and feminized) start the flowering stage when the nights are sufficiently long and there is no light in the night (12/12 is the usual setting).^[7]

Feminized seeds are the easiest first selection. With autoflower seeds, you do not set the time of flowering. Regular seeds are for breeders.
	Regular	Feminized	Autoflower
Sex of the plants	Approximately 50% male and 50% female	Approximately 99% female	Feminized autoflower seeds: approximately 99% female. Regular autoflower seeds: approximately 50% male and 50% female.
Flowering trigger	Change the light cycle to 12h light	Change the light cycle to 12h light	Automatic, at a specified age
Time to harvest	Longer than autoflower	Longer than autoflower	Approximately 60-90 days after germination
Plant size	Large	Large	Approximately 60–120 cm (2–4 ft)
Possible yield	High	High	Lower for each plant
Easy for a new grower	No (you must find the male plants and remove them)	Yes (the easiest)	Yes (no task to set the time of flowering)

Photoperiod and autoflower plants

Photoperiod plants start the flowering stage when the nights are sufficiently long (growers usually use 12 hours of light and 12 hours of darkness). Autoflower plants start the flowering stage at a specified age. The light cycle has no effect on this.

Primary information 3

Germination methods

To start germination, you give the seed three conditions: water, a warm temperature, and darkness. Darkness is optional. The embryo absorbs water and becomes larger. Then the taproot comes out through the seed coat. There are three usual methods to give the seed these conditions.

In the paper-towel method, you put the seeds between moist paper towels, and you put the towels between two plates. Growers use this method the most, because they can see the taproot. With new seed, and with control of the moisture and the temperature, a high germination rate is frequent.^[2] The one risk is that you cause damage to the weak root when you move the seed to its pot.

All three methods supply water and a warm temperature. Darkness is optional. The primary difference is that with some methods you can see the progress, and with other methods you cannot.
Method	View of the progress	Transplant risk	How easy	Best for
Paper-towel method	High (you can see the root)	Average (touch the root carefully)	Easy	Most new growers
Direct-sow method	None (the seed is in the medium)	None	Easy	When you do not want to touch the root
Pre-soak method	Some (the seeds fall in the water and become larger)	Low	Easy	Aged seeds or seeds with a hard seed coat

Figure 3. Use towels that are wet but have no free water. Put the seeds apart on a towel, and put a second towel on them. Keep the seeds warm and dark. Examine the seeds two times each day. Plant the seed when the taproot is approximately 0.5–1.5 cm (0.2–0.6 in) long.^[3]

The direct-sow method and the pre-soak method

Direct-sow: Plant the seed in the moist medium at a depth of approximately 1–1.5 cm (0.4–0.6 in), with the taproot down. There is no transplant shock, but you cannot see the progress.
Pre-soak: Soak the seeds in water at room temperature for 12-24 hours. The seed coat becomes soft. Use this method for aged seeds or for seeds that have a hard seed coat. After this, move the seeds to a towel or to the medium.

Seedling in rockwool and coco in a humidity dome — Example. The roots continue to absorb the water. A humidity dome decreases the quantity of water that the air removes from the leaves. This effect does not show that the seedling absorbs water through its leaves.Fact check

By stage

Germination conditions and time sequence

The environment has an effect on seeds. Three conditions are important: temperature, moisture, and light. When all three are in the correct range, most viable seeds germinate with no other aid.

Keep the temperature at a stable 21–25 °C (70–77 °F). A lower temperature makes germination slower. A temperature that is higher, or that changes, causes seeds that do not germinate.^[3] Keep the medium or the towel moist, but do not make it too wet. Keep the seeds moist and warm until they germinate (darkness is optional).

Figure 4. Use a temperature in the green zone and keep it stable. Changes of temperature, and a temperature of more than approximately 28 °C, are a frequent cause of seeds that do not germinate.^[3]

Figure 5. The taproot usually comes out of the seed in 24-72 hours (a maximum of approximately 7 days for some seeds). The cotyledons open after some days. The first true leaves come at approximately days 7-14. At approximately day 21, the seedling is strong.^[2]

The three conditions

Temperature: a stable 21–25 °C (70–77 °F). Do not let the temperature change, and do not let it become more than approximately 28 °C.
Moisture: moist, but not too wet. A seed that is too wet cannot get oxygen, and it rots.
Light: darkness is optional during germination. After the seed germinates, immediately give light of low intensity, to prevent a stem that is too long and thin.

By stage

Seedling procedures in the first two to three weeks

The seedling transpires water through its leaves. The rate is higher than the rate at which the small root system supplies water. Dry, warm air removes water from all objects near it, and from the leaves of the seedling. Air with high humidity has almost the maximum quantity of water, and it removes much less water.

The vapor pressure deficit (VPD) is the difference between the quantity of water that the air can hold and the quantity that it holds. The unit is kPa. VPD shows how strongly the air removes water from the leaves. When the VPD is lower, the air has more humidity and removes less water from the leaves.

For the first two weeks, keep the VPD at 0.4–0.8 kPa (65–80 % relative humidity, RH).^[9] A humidity dome, or a transparent bag with vents, above the seedling can keep this range easily for the first 7–10 days.

Keep the light intensity low. In the first week, use approximately 100-200 PPFD. In week two, use 200-300 PPFD (a DLI near 10-15). Keep the LEDs at a large distance from the seedlings. This distance prevents stems that are too long and damage to the leaves from the light.^[8]

PPFD is the quantity of light that falls on the plant at this time and that the plant can use. DLI is the total quantity of light that the plant receives in one day.

At first, do not apply feed. The cotyledons supply the nutrients for the plant. Start with a weak nutrient solution, at approximately 25 % strength, only when the first true leaves show. The first true leaves show in approximately weeks 2–3.

EC (electrical conductivity) shows the quantity of nutrients that are in the water. If the EC is too low, the plant does not get sufficient nutrients. If the EC is too high, the plant has nutrient burn. At this stage, use an EC of approximately 0.3–0.8 mS/cm.

Apply only a small quantity of water, around the bottom of the stem. Between the times that you apply water, let the surface become less wet. Then the roots become longer, down in the medium, and find moisture.

Targets for the seedling in each week. At the start, use a high humidity and weak light. Then decrease the humidity slowly, and increase the light and the feed slowly.
	Week 1	Week 2	Week 3
Humidity (RH)	70-80%	65-75%	55-65%
VPD (kPa)	0.4-0.6	0.6-0.8	0.8-1.0
Light (PPFD / DLI)	100-200 / approximately 10	200-300 / approximately 13	250-350 / approximately 15
Feed EC (mS/cm)	None (water only)	Approximately 0.3-0.6, when the true leaves show	Approximately 0.6-0.8
Apply water	Spray, or a small quantity of water, near the stem	A small quantity. Let the surface dry.	A larger quantity than in week two, but the quantity is small

Figure 6. When the light is at a large distance, the seedling becomes long, thin, and weak. At the correct distance, the seedling stays short and thick. This shape is correct.^[8]

Two errors of new growers

Do not apply too much water. Do not apply feed before the correct time. These two errors kill more seedlings than all other causes. If you are not sure, apply less water and apply feed after more time. A seedling with a small nutrient deficiency can be in good condition again. A seedling with rot cannot.

When a problem occurs

Troubleshooting

Damping-off is the disease that kills the most seedlings. Soil fungi such as Pythium, Fusarium, and Rhizoctonia cause this disease. A seedling that was in good condition suddenly becomes thin and black at the soil surface, and it falls. When the disease starts, it almost always kills the seedling.^[10]

The primary cause is too much water, together with a humidity that is too high and low airflow. Thus it is better to prevent the disease than to apply a treatment. Use new, sterilized medium. Apply a small quantity of water. Add a weak circulation of air. When the true leaves show, decrease the humidity to 40-50%.^[11]

Figure 7. Stop the sequence at the start. Apply less water, increase the airflow, and decrease the humidity after the true leaves show. When the fungus is in the stem, it usually kills the seedling.^[10]

Find the cause for each symptom. For most problems, the correction is to apply less water and less feed, and to give more air.
Symptom	Usual cause	Procedure
The stem rots and falls at the soil surface	Damping-off (too much water, high humidity, no air movement)	Remove the seedling. Let the medium dry. Increase the airflow and decrease the humidity. These tasks only prevent the disease.
The seed does not germinate	Aged seed or immature seed. The temperature is too low. The seed is too deep in the medium. The seed became dry.	Use new seed. Keep the temperature at 21–25 °C. Plant the seed at a depth of 0.5–1.5 cm (0.2–0.6 in). Keep the medium moist.
A stem that is long and thin	The light is too weak or too far from the seedling	Move the light nearer to the seedling, or use a light with a higher intensity. At the transplant, put the stem deeper in the medium.
Dry leaf tips (tipburn)	Feed applied before the correct time, or feed that is too strong	Stop the feed and apply only water. Then start the feed again at approximately 25% strength.
A seedling that becomes yellow	Too much water, or feed that you applied before the correct time	Let the medium become less wet. Do not apply nutrients until the true leaves show.

There is no treatment for damping-off

Prevent damping-off. Use new, sterilized medium. Apply a small quantity of water. Give good airflow. After the true leaves show, decrease the humidity to 40-50%.^[11] When the bottom of a seedling becomes thin, the seedling cannot be in good condition again.

Check of the results

Expected results and limitations

Not all seeds germinate, also when the seeds are good and the procedure is careful. New feminized seed of good quality frequently has a germination rate of much more than 90%. But one or two seeds that do not germinate are usual. They do not show that you did a task incorrectly.^[1]

Figure 8. New seed of good quality has a high germination rate. A high age, immature seed, and bad storage all decrease the rate.^[2]

The time from the day that you plant the seed to a strong seedling with some groups of true leaves is approximately 3-4 weeks. After this time, the vegetative growth of the plant increases quickly. Germinate one or two more seeds as a precaution. It is possible that the problems in this paper kill a small number of seedlings. Do not apply too much water, and do not apply feed before the correct time.

Good results

A high germination rate is usual for new seed of good quality. But it is possible that one or two seeds do not germinate, also when you do all tasks correctly.
The time from the day that you plant the seed to a strong seedling is approximately 3-4 weeks. After this time, fast growth starts.
Germinate one or two more seeds as a precaution. It is usual for a new grower that a problem kills a seedling from time to time.
The two errors that kill the most seedlings of a new grower are too much water and feed applied before the correct time. It is safer to apply less water and less feed.

In these first weeks, a slow and careful procedure gives the best results. When your seedling is strong, read the paper on light acclimation. It shows how to increase the light safely. Also read the paper on mold risk, because the humidity decreases at this time. For the next cultivation, you can use cloning and not seeds. Cloning gives you an accurate copy of a plant that you know is good.

References

Small, E. (2017). Cannabis: A Complete Guide. CRC Press. [Seed storage] See also: Vejl, P., et al. and foundational work on Cannabis seed longevity. PRIMARY: Tipparat, P. corrected to, Lipid oxidation and seed viability: see Cockson et al. 2025 (cited separately). https://www.tandfonline.com/doi/abs/10.1080/15440478.2012.737179
Cockson, P., et al. (2025). Impact of seed moisture and temperature on hemp (Cannabis sativa L.) seed germination. Agrosystems, Geosciences & Environment, 8(1), e70129. https://doi.org/10.1002/agg2.70129 https://acsess.onlinelibrary.wiley.com/doi/10.1002/agg2.70129
Smith, T., et al. (2022). Temperature Limits for Seed Germination in Industrial Hemp (Cannabis sativa L.). Crops, 2(4), 415-427. https://doi.org/10.3390/crops2040029 https://www.mdpi.com/2673-7655/2/4/29
Flajsman, M., Slapnik, M., & Murovec, J. (2021). Production of Feminized Seeds of High CBD Cannabis sativa L. by Manipulation of Sex Expression and Its Application to Breeding. Frontiers in Plant Science, 12, 718092. https://doi.org/10.3389/fpls.2021.718092 https://pmc.ncbi.nlm.nih.gov/articles/PMC8591233/
Monthony, A. S., Page, S. R., Hesami, M., & Jones, A. M. P. (2021). pH and chemical sterilization / sex induction in Cannabis. See: Optimized guidelines for feminized seed production in high-THC Cannabis cultivars (2024). Frontiers in Plant Science, 15, 1384286. https://doi.org/10.3389/fpls.2024.1384286 https://pmc.ncbi.nlm.nih.gov/articles/PMC11557428/
Toth, J. A., Stack, G. M., Carlson, C. H., & Smart, L. B. (2022). Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science, 13, 991680. https://doi.org/10.3389/fpls.2022.991680 https://pmc.ncbi.nlm.nih.gov/articles/PMC9533707/
Moher, M., Jones, M., & Zheng, Y. (2023). Is Twelve Hours Really the Optimum Photoperiod for Promoting Flowering in Indoor-Grown Cultivars of Cannabis sativa? Plants, 12(14), 2605. https://doi.org/10.3390/plants12142605 https://pmc.ncbi.nlm.nih.gov/articles/PMC10386198/
Rodriguez-Morrison, V., Llewellyn, D., & Zheng, Y. (2021). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science, 12, 646020. https://doi.org/10.3389/fpls.2021.646020 https://pmc.ncbi.nlm.nih.gov/articles/PMC8144505/
Zhang, D., Du, Q., Zhang, Z., Jiao, X., Song, X., & Li, J. (2021). Minimizing VPD Fluctuations Maintains Higher Stomatal Conductance and Photosynthesis, Resulting in Improvement of Plant Growth in Lettuce. Frontiers in Plant Science, 12, 646144. https://doi.org/10.3389/fpls.2021.646144 https://pmc.ncbi.nlm.nih.gov/articles/PMC8049605/
Lamichhane, J. R., Durr, C., Schwanck, A. A., Robin, M.-H., Sarthou, J.-P., Cellier, V., Messean, A., & Aubertot, J.-N. (2017). Integrated management of damping-off diseases. A review. Agronomy for Sustainable Development, 37, 10. https://doi.org/10.1007/s13593-017-0417-y https://link.springer.com/article/10.1007/s13593-017-0417-y
University of Minnesota Extension. (n.d.). How to prevent seedling damping off. UMN Extension. (source not from a journal, for example from a manufacturer) https://extension.umn.edu/solve-problem/how-prevent-seedling-damping

Each citation in the paper, for example [1], refers to an item in this list. Each item is a primary source or an instruction from an authority, unless the item shows a different type. The results of cannabis tissue culture change much with the genotype. Before you use the dilutions, hormone doses and local regulations, make sure that they agree with the primary sources.