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Why Are My Seedlings Growing So Slow?

Why are my seedlings growing so slow

Cannabis plants require specific conditions to grow properly, and growth can be slow when those requirements are not satisfied. You can do a few things to assist your slow growing plants. This article will teach you how to care for cannabis seedlings, some common problems that may develop, and how to solve them.

Environmental conditions for the growth of cannabis seedlings

Are your environmental controls on point? If not, utilize these target ranges to help find the sweet spot for efficient cannabis seedling growth.

  1. Warm temperatures: Seedlings are extremely temperature sensitive; they thrive in temperatures ranging from 72 to 79° F (22 to 26ºC). Temperatures between 77°F and 25°C are ideal for seedlings. When the lights are turned off at night, a temperature of 65°F – 18°C can help reduce stem elongation and internode spacing.
  2. Relative humidity: If your environment is extremely dry, your seedling may quickly dry out. Maintain humidity levels of 60-65%. Burnt leaf tips may indicate a lack of humidity.
  3. Light or photoperiod: Begin with 18 hours of light and 6 hours of darkness.
  4. Nutrients: Seedlings require no to a low dose of nutrients or will experience nutrient burn. If growing in soil, choose light mixes and avoid using extra fertilizer for the first week or two. After that, you can begin your fertilizing strategy.
  5. Pot size: Once your seedling has germinated, place it in a small pot or cup with drainage for best results. Then, transplant it to a larger pot once your seedling has grown a few centimeters or you see cannabis roots coming out of the drainage holes.

Common reasons for the slow growth of your cannabis seedling

Why are my cannabis seedlings taking so long to grow? Many factors, such as light, water, nutrients, or temperature, can cause stunted growth in the seedling stage. The following are the most common reasons for slow seedling growth.

Old or low-quality seeds

Old seeds take longer to germinate (if they germinate), and plants grown from old seeds may also grow slower. Similarly, good genetics are required for healthy, vigorous growth from seed to harvest. A random bagseed will not outperform quality seeds obtained from a credible seedbank.

Problems with nutrients

Nutrient toxicity occurs when the growing medium contains excessive nutrients for the seedling stage, and the plants cannot absorb them. If this is the situation, the leaves will have burnt tips and a dark green color. This is common in soil mixes with a high percentage of nitrogen or slow-release nutrients.

Nutrient deficiency can occur due to the growing medium lacking or having too much of them, causing pH levels to be off and those nutrients not being available for the cannabis plant to uptake despite being present in the mix. Nitrogen deficiency is the most prevalent at this stage, with older leaves turning yellow, brown, and crispy.

This can also happen when the plant is in a small pot and has depleted all of the nutrients in the soil. If this is the case, it is ideal to transplant it into a larger pot with a soil mix and applying nutrients during the vegetative stage. Remember to keep track of watering schedules for the best results.


One of the most prevalent mistakes made by novice cannabis growers is overwatering. It’s like suffocating your plants, one of the main causes of slow growth, nutrient deficiencies, root rot, fungus, and many other issues. Water sparingly and not on a normal basis. Watering less frequently allows the soil to dry between waterings. Lifting the pot itself is a good way to see if you should water it. It is time to water again if it feels quite light.

Issues with pot size

Cannabis growers frequently start seedlings in small cups. When the plants have grown sufficiently, they will “pot-up” to larger containers. If you start your cannabis plants in too large containers, you run the risk of overwatering them. The problem is that seedlings cannot absorb all of the moisture held in a large container, whereas mature cannabis can “drink” much more. Conversely, a large pot will take much longer to dry out.

Additionally, to avoid problems caused by too much moisture and soil, start seedlings in smaller containers until they are vigorously growing. Transfer your seedlings to a larger container, at least twice their current size, once they have a set of 5-6 real leaves (not counting the cotyledons). If your seedling is already in a large container and you do not desire or can’t move it to a smaller cup, water only the area around it.

Too low or high temperatures

Seedlings will experience stunted growth if temperatures are too high or too low. This is evident by the tips of the leaves curling and turning up. If this is the case, lower the temperature of the environment and keep an eye out for changes. Keep the environment temperature between 72 and 79 Fahrenheit (22 and 26 degrees Celsius).

Furthermore, the ideal temperature for cannabis seedlings is between 77°F and 25°C. When the lights are off at night, a temperature of 65°F – 18°C can significantly reduce stem elongation and internode spacing.

Issues with light

Stunted growth can also be caused by too much or too little light. As the seedling grows, increase the intensity of the light. Seedlings need more light to develop very tall, weak stems with few leaves. The stem becomes tall and white. If this is the case, move your growing light closer to the plant. Always perform the “hand test,” which involves placing your hands on top of your plants for 30 seconds. So, if it’s too hot for your hand, it’s probably too hot for the cannabis plant, so raise your lamp until it’s warm but not hot.

Although LED lights do not produce much heat, they can burn the plant if placed too close. Maintain the recommended distance by following the manufacturer’s instructions. When seedlings are exposed to too much light, their leaves curl and appear burnt. Move your lights up and perform the “hand test” if this is the case.

Damping-off – Fungi infection

Overwatering may cause “damping off,” a very common fungi-caused disease. Some of the fungi that cause damping off are Pythium, Botrytis, and Fusarium; they all appear with high humidity and cool temperatures below 68°F – 20°C. A damping-off seedling has spots on the stem’s base and seems weak and thin. The stem bends just above the topsoil within a few days, and the seedling dies. You can do nothing to save the cannabis seedling when it falls over.

Furthermore, to avoid damping off, don’t overwater or fertilize your cannabis seedling for the first week, and keep the relative humidity low. If one seedling has already died due to damping off, remove it as soon as possible before the fungi spread to the other cannabis plants. Also, use a 3% hydrogen peroxide solution to sterilize the environment.

Cannabis root health

Metabolic functions slow down when your plant’s roots do not receive enough oxygen. In some cases, a lack of oxygen may completely halt their growth. Overwatering or using substrates with poor drainage are two common causes. What should be done? Make a growing medium that is light and airy, with good drainage. You can use perlite to improve poor-draining soil.

Deep Water Culture Roots
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Your cannabis plants’ root zone should never be much hotter or colder than room temperature. Similarly, physical damage to the roots, mold, or bacteria can all harm the growth of your plants. Always use non-transparent planters to prevent light from reaching the roots, which is also harmful.

An overview of cannabis seed shell stuck on the seedling

A cannabis seed has just sprouted, but the seed shell is still attached to the seedling. How should you proceed? The seed shell usually falls off when the first pair of round leaves (cotyledons) form. This shell can become very hard and become attached to the already-formed cotyledons. You can soften the shell by spraying it with clean water and leaving it for a few hours. If you decide to remove it, spray it lightly with water and gently remove the shell with sterilized tweezers. Take extreme caution not to harm the seedling!

When to transplant your cannabis seedlings

When should I move my seedlings? If the cannabis seedlings are in cups, jiffies, or plugs, they should be ready to transplant to the next container in about a week. It’s time to transplant when the seedling’s leaves reach the edge of the cup or the roots reach the bottom and begins to show through the drainage holes. Don’t expect the seedling to continue growing if you don’t transplant it; each plant grows only as much as the containers allow. Too much time in a cup for cannabis seedlings will result in stunted growth. Lost weeks in a small container for an autoflowering plant can result in smaller adult plants.

Moreover, when transplanting, take extra care not to damage or touch the fine roots. Prepare the next pot with the preferred medium and water immediately following the transplant. If everything goes well, the seedling should continue to grow every day. When there is root damage, it may take a few days for the seedling to repair and grow more roots before it can resume growing the stem and leaves.

Cannabis plants are incredibly vulnerable and sensitive at the seedling stage because their root system has not yet developed and require special care, moderate watering, and humidity. A healthy cannabis seedling has a short stem and green leaves. Gather information about this stage and keep track of your environmental factors. Luckily, your seedling will quickly grow and progress to the next phase of a healthy plant!

Picture of Marcus Smith

Marcus Smith

Marcus is a relative newcomer to the cannabis world. Though it may seem that his youth wouldn’t allow for a wealth of knowledge, this is untrue. Marcus Smith has close relationships with many cannabis breeders and grow owners which have allowed him to sample the best cannabis across the US and beyond while also gaining valuable insight into how different strains grow and develop. About this Author

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