How To Grow Marijuana in the Seedling Stage - 5 Tips to Get Growing

Seedling stage | How to grow marijuana from seed
Estimated 6 min to read
June 06, 2021

By now hopefully, you’ve had your seed(s) successfully sprout and begin growing their taproot and first set of leaves (if not, follow my guide here to learn the best methods to germinate your marijuana seeds). Congratulations - waiting for your seeds to sprout is the most nerve-racking part of the growing process. The rest of the lifecycle for your marijuana plant is straightforward because you have control over the future of your plant.

5 Tips to Get Growing

Temperature, humidity, and lighting are the largest factors that impact seedling growth rate and health. Additionally, perfecting the nutrients, water and airflow will help your seedling start as optimally as possible. The following are tips in each of the sections to help you develop your seedling into a mature plant as quickly and healthily as possible.

1. Temperature & Humidity

As with any seedling, cannabis seedlings will grow slower if they are not exposed to the proper humidity and temperature levels. High temperatures will stress your seedlings and can potentially stunt their growth. At such an early stage, this can prove fatal for you marijuana plant and at the very least set your it’s growth back. Cold temperatures can affect its ability to transport and use nutrients, water, and oxygen and can even inhibit growth altogether, making it go into a hibernation state. This will result in stunted growth and eventually death if not dealt with properly. The range of temperatures between 70 and 77 degrees Fahrenheit (around 20-25 celsius) is the optimal range for seedlings.

Novice growers tend not to take into account temperature increases from grow lights. Depending on the type of bulb and proximity to the seedlings, grow lights can create a lot of heat which can stunt plant growth

Humidity is also very important for your marijuana plant in the seedling stage. Humidity levels that are too low can dry out your seedling, stunting its growth. It can even cause nutrition deficiencies when the plant is so young and susceptible. High humidity levels attract mold and fungus which compete with the seedling for nutrients which can also result in nutrient deficiencies. The optimal relative humidity level is between 40-60% within the grow space.
ThermoPro TP50
Cheap and reliable thermometer and humidity gauge
This is the temperature/humidity gauge that i've always came back to, and recommended. I've never had any issues after owning it for years, and its always been very accurate. It measures temperature/humidity changes relatively quickly too. With 80,000 reviews and 4.6/5 stars and costing less than $11, you cant do much better.
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2. Lighting

You should be careful about giving your seedlings too much light, as it can easily stunt growth or burn their leaves. LED and other high output lights used for vegetative and flowering stages are often too bright for seedlings. The most common seedling light schedule is 16-18/8-6 meaning 16-18 hours of light and 8-6 hours of darkness. Too little light will result in slower growth of your seedling.

Many growers opt for lower-power fluorescent lights for the seedling stage. There are a few benefits to this, but mainly so you don’t overwhelm your plant at the early stages of its life cycle. Additionally, some growers like to have multiple lighting setups for seedling, vegetation, and flowering stages as they all require different amounts of light.

This Barrina shop light would be a good choice, as its cheap (<$20) and well reviewed.
Barrina shop light
A cheap and highly related shop light for seedlings
When in the seedling stage, you dont want to cook your plants with a high-output light. This Barrina light offers an optimal amount of light for seedlings, is well reviewed and costs less than $20.
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3. Nutrients

The level of nutrients you need to supplement your seedling highly depends on what medium you are using. Additionally, seedlings are very sensitive to nutrient levels, and seeing nutrient burn in seedlings is common.

Soil based mediums

For soil-based mediums, you shouldn’t add any additional nutrients to your plants during the seedling stage. Seedlings will have enough nutrients for about 3-4 weeks after germination from nutrients stored in their seed.

Soil-less based mediums

Soil-less mediums like coco coir, Rockwool, and hydroton, don’t provide any inherent nutrition to your plant, and therefore you need to provide your seedling with all of the nutrients they will require. With that said, seedling’s nutrient requirements are very small, and you will likely be able to get away without adding any additional nutrients for the first 3-4 weeks. If you begin to see signs of nutrient deficiency (yellowing of the leaves), try using the nutrient formula described in this article at 1/2 strength.

4. Water

One of the major components of successfully growing an indoor marijuana crop (for all stages, including seedling) is allowing excess water to drain away from the plant while it’s growing. When this happens, excess water will not pool at the base of the plant resulting in overwatering complications. Overwatering is due to the plant not getting enough oxygen because it’s saturated with water - resulting in drooping leaves which can sometimes be confused with underwatering. Don’t make this mistake - if the soil is wet, and your plant is drooping, it’s likely because you are watering it TOO MUCH. Additionally, overwatering can dilute the nutrient balance of the medium resulting in nutrient deficiencies (especially towards the beginning of the vegetation stage - this isn’t as important during the seedling stage). To help prevent this from happening, it’s best to only water the plants when the medium has dried out to the touch, and ensure the pot has adequate drainage holes.

Product suggestions

  • Fabric pots are rapidly becoming popular for marijuana growers, because of their numerous benefits

    • They are very easy to store while not being used
    • They allow greater airflow through the growing medium which enhances growth rates
    • They drain excess water very well to avoid over watering
  • Pot elevators are used to make sure your plant isn’t sitting in the water that drained out

  • Adding perlite to your growing medium can improve water drainage.
VIVOSUN 5 Gallon Grow Bags
Standard 5 gallon grow bags, improves soil aeration and reusable!
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Grow Pro pot elevator
A good thing to elevate your pot 😉
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5. Airflow

Seedlings do need some airflow, but it is very easy for your plant to get too much. Do not have a fan blowing directly on your seedling, as that is likely to dry it out and stunt its growth. Instead, it is best to have indirect airflow, either through your grow tent or naturally. Additionally, your plant’s roots need a good flow of oxygen to for proper growth. In addition to fabric pots suggested above, you can also add perlite perlite to your growing medium to improve aeration.

If you follow our beginner’s guide, you’re very likely to have a fruitful harvest from your first crop of seedlings. All you have to do is take care of your growing operations properly and be patient and vigilant. Before long, you’ll be a master of growing and you’ll be making high-quality, award-winning buds in no time. See our nutrient guides for vegetation and flowering for hydroponics here and for soil-less mediums like coco coir here.


Q: How long does the seedling stage last? A: Under normal circumstances, seedling stage lasts anywhere from 1-3 weeks. A plant is considered in the seedling stage after the first set of leaves are developed, until they have around three to four sets of “true” leaves (leaves that look more like traditional marijuana leaves).

Q: Why does my plants first leaves look different? A: The first set of leaves developed in most plants, including marijuana, are called cotyledon leaves. Cotyledon leaves look different and are functionally different than adult “true” leaves. This is completely normal, and the plant should be growing its first set of true leaves soon afterward.