Article written by
Homegrown Cannabis Co.American Seed Bank and Cultivation Experts
Content reviewed by
Dr. Lewis JasseyMedical Director - Pediatric Medicine
Table of contents
The cannabis seedling stage is a sensitive and significant section of the growing process. It comes after the germination stage and before the vegetative and flowering stages. During this key stage, the first real roots and fan leaves appear.
A marijuana seedling is fragile. These sprouts thrive in moderately warm, highly humid conditions and don’t take well to stress. They need protection to grow into robust vegging plants. Provide proper TLC, and you set yourself up for abundant harvests.
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What Is the Seedling Stage?
The seedling phase is the second cannabis growth stage and spans the first 2-3 weeks after germination. Throughout this time, a sprouted seed becomes a tiny marijuana plant with those iconic seven-fingered leaves.
This stage begins when you place a germinated seed into a growing medium.
Two rounded leaves (cotyledons) develop directly from the seed. New blades soon emerge from the previous pair, displaying more ridged edges. You eventually get seven-fingered blades.
As greenery develops above ground, the root system expands below. The taproot branches into secondary and tertiary tubes, spreading through the soil to chase water.
During the earliest life stage, cannabis gets its energy from nutrient stores inside the seed. It’s yet to develop a dense canopy and a robust root zone and start sustaining itself through the outside environment. That’s why it performs best in an artificially optimized environment until you see true leaves and vegetative growth commences.
What Does a Healthy Seedling Look Like?
Rapid growth and brilliant green color are the telltale signs of a healthy seedling. The stem is thin, and the leaves are slightly tilted upward. The plant is thick with vegetation, and its roots are long, white, and fiber-like.
Healthy plants vary in appearance when they mature, but seedlings are pretty uniform. Deviations from our description hint at health issues. Here are some common health issues and what you can do to address them:
- Droopy leaveswith tips curled under suggest excessive watering and a lack of oxygen. Start seedlings in small containers and use a well-draining medium.
- Yellow and wilting leaves point to your plants being rootbound. Transplant to a bigger pot to rejuvenate them.
- Slumping and shriveling happen due to fungi living in the soil. Weed botrytis may also appear. We call this process damping off, and you can prevent it by keeping the space clean and moderately warm.
- Wilting, bending, and stunted growth result from underwatering. Mist your seedlings more often and water the soil to fix the problem.
- Dark foliage and brown leaf tips occur when the medium is over-fertilized. Flush the soil of excessive minerals and remove the leaves too damaged by the nutrient burn.
- Soft, folded, and yellow leaves happen due to nutrient deficiencies, especially nitrogen. Keep a close eye on the pH and supply a gentle fertilizer like worm castings to prevent this problem.
- Crispy and upward-curled leaves occur in excessive heat. Never let the environment surpass 77°F to avoid overheating your seedlings.
- Slim stems with large internodes are a consequence of inadequate light. Seedlings reach upwards to try and find the sun and may tip over. Check the manufacturer’s instructions and move your lamp as close to the plant as is safe. Bury the extra stem in the soil.
- Pale, burned, and crinkled leaves tell you that the plant is too close to the light source. Reduce the intensity and trim away the dying foliage to resolve the issue.
Tips for Growing Healthy Cannabis Seedlings
Growing weed can be as simple as dropping a seed into the ground and letting it sprout and develop. You get more reliable results when you’re mindful of its surroundings, though. Here are a few tips specific to seedling care.
Start With Superior Genetics
Growing marijuana goes best when you have top cannabis seeds. They should be mature, undamaged, and well-sourced to sprout and develop into healthy plants.
Shop with a reputable seller like Homegrown Cannabis Co. Their regular, autoflower, and feminized seeds contain superior genetics and come with germination guarantees.
Choose the Right Container
A marijuana seedling needs appropriate space to grow; having too much or too little breathing room can cause plant health problems.
Overly small containers make roots wrap around themselves, hindering their ability to absorb water. Stunted cannabis growth is another common consequence of limited spaces. The plant can’t consume all available moisture when the pot is too spacious.
Sow your germinated seeds in solo cups with drainage holes for the fastest growth rates.
Use Lightly-Fertilized Soil
Marijuana seeds contain nutrients that sustain a seedling for the first 1-2 weeks. After using this food, plants require small amounts of nitrogen, phosphorus, and potassium from the soil.
You could purchase a seedling-specific potting mix from a gardening store or supply a quarter-dose of the best cannabis nutrients.
Employ a Humidity Dome
Seedlings have small root systems which can’t absorb enough water from the soil; they compensate by drinking through their leaves. For this reason, they develop best in moist environments (60-70% relative humidity).
You can ensure optimal conditions by installing a humidifier in your grow room, but a dome is cheaper and more effective. It also protects the weed plant from pests and pathogens.
A humidity dome is a transparent glass or plastic cover over the pot. You can use a plastic bottle or a cake box. Moist air remains inside, and there’s no risk of your seedling drying and dying.
Expert tip: Clean the dome and wipe away excess moisture daily.
Skip LED and HPS Lamps
Seedlings require 18 hours of light and six hours of darkness each day. The lamp type also plays a role in their development.
Vegging and flowering plants perform well under LED or HPS lamps, but not seedlings. LEDs without dimmable ballasts are usually too intense, while HPS produces excessive heat. Fluorescent lights with cool, blue-green spectrums have the best results.
Expert tip: Some growers keep cannabis seedlings under CFLs for 24 hours, but an 18/6 light cycle leads to higher growth rates. As a bonus, you spend less on electricity when the lamp isn’t active all the time.
Strengthen the Stem
A healthy cannabis plant has a robust stem to support its branches and foliage. Seedlings sometimes stretch too thin due to the external environment, though. If this happens, apply stress to the stalk to strengthen it.
Take the stem between your fingers and bend it back and forth. The pressure forces it to tear and rebuild, becoming much sturdier. Since seedlings are vulnerable when very young, only use this technique when the plant is at least eight inches tall.
Know When to Cut Your Losses
Even if you do everything right, some seedlings might get too sick to survive. Most notoriously, you can’t reverse fungal damage on young marijuana when the stem already shrivels and goes brown. If it happens, remove that plant from the humidity dome. Otherwise, pathogens spread to healthy sprouts.
Download Our 7 Page Guide to Growing Cannabis
Caring for a Cannabis Seedling Step by Step
You now have an idea of what your seedlings need to thrive. Let’s see which steps to take during the first few weeks of growing cannabis.
1. Optimize the Environment
Marijuana seedlings enjoy warm temperatures and high relative humidity. They do best in a 68-77°F temp range (59-68°F at nighttime). Air moisture levels of 65-70% help them remain hydrated.
Young plants don’t adapt to weather extremes, so stay on top of climate control for the first 3-4 weeks of their life cycle. If possible, automate your devices to eliminate fluctuations in your growing environment.
Expert tip: Even if you’re planning to grow weed outdoors, keep your seedlings inside till they have three nodes. Only take them outside when the weather is consistently warm in early May.
2. Sow Your Seedling
Once the germination process is complete, it’s time to sow your seed.
Use tweezers to pick up a sprouted seed and move it to a solo cup with a potting mix. Put it down taproot-side first and loosely cover it with soil. Lightly spray the surface with water to help it settle.
3. Position Your Light Right
Place a fluorescent lamp above the soil, following the manufacturer’s instructions on distancing. Automate it to shut down after 18 hours to keep a consistent light schedule. Maintain the correct distance between the plant and the bulb as the seedling stretches.
4. Mist the Seedling Daily
While the seedling is very young, it may drown in overly moist soil. To avoid this, fill a spray bottle with slightly acidic water (5.8-6.5 pH) and mist the cotyledons and soil surface daily.
You can transition to soil watering when the first fan leaves emerge. Only pour around the stem and rely on frequency rather than quantity.
5. Check for Signs of Ill Health
Check your cannabis seedling daily for visual signs of trouble, like drooping, discoloration, curling, or stretching. Consult our list of health issues and act accordingly as soon as you notice a symptom.
5. Transplant Your Seedling
Transplanting enables further growth when the seedling gets too large for a solo cup. It should occur when the leaves cover the container circumference, and the roots protrude from drainage holes.
You have two options:
- Planting straight in the final container: Choose a three-gallon pot for compact autos and a five-gallon or seven-gallon bucket for larger photoperiods. Growth is less explosive at first, but you minimize the risk of shock.
- Potting up: Gradually increase the container capacity as the root system expands in the vegetative phase. Growth is more intense, but you should watch for transplant shock. In this case, move your plant to a one-gallon or two-gallon pot.
In either case, disinfect your environment to remove pathogens before doing anything else. Wait for the soil to become somewhat dry (but not completely, as seedlings are vulnerable to drying out). Consider transplanting just before the lights-off hours to give your plant time to recover.
Prepare another pot with fertilized, moist soil. Loosen the root ball by gently squeezing the sides of your cup and pushing it outward. Keep the pressure minimal to avoid disturbing the roots. Once the seedling is out, place it in the new container and water it immediately to help it settle.
Once your plant is in a larger container, it’s time for a new and exciting step: the vegetative stage.
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Frequently Asked Questions
Should you water autoflowers every day?
Watering frequency depends on the pot size and weather. In general, cannabis plants from autoflower seeds require moisture daily in hot, dry climates and small pots (up to three gallons). Larger pots (five or seven gallons) in humid areas need water every other day.
You can gauge whether more water is necessary by lifting your pot and touching the soil. If the container is very light and the top inch of the medium feels dry, it’s time for another shower.
How high should my light be for seedlings?
The correct distance to hang a light depends on intensity and heat. In general, a fluorescent lamp should sit several inches above your plant. HPS grow lights are stronger and run hotter, so they must stay farther from seedlings. Keep them as close as possible while ensuring the temperature doesn’t surpass 77°F.
Slim and stretchy stems signal that the lamp is too far from your seedlings. Dry and burnt foliage lets you know the lamp is way too close to the plant.