When to Start Fertilizing Cannabis Seedlings

It’s generally recommended that you wait to fertilize your cannabis seedlings until they have their second set of true leaves.

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Fertilizing your cannabis seedlings is a vital step in ensuring a healthy, productive crop. But when is the best time to start fertilizing?

There are a few factors to consider when determining when to start fertilizing your cannabis seedlings. One is the type of fertilizer you will be using. Another is the age and size of your seedlings.

If you are using a water-soluble fertilizer, you can begin fertilizing as soon as your seedlings have their first true leaves. If you are using a slow-release fertilizer, you should wait until your seedlings are a few weeks old and have several sets of true leaves.

The age and size of your seedlings will also dictate how much fertilizer you need to use. As a general rule, you should use 1/4 to 1/2 teaspoon of fertilizer per gallon of water. Seedlings that are just starting out may need less fertilizer, while older, larger seedlings may need more.

It is also important to remember that cannabis plants are susceptible to fertilizer burn. This can happen if you use too much fertilizer or if the fertilizer is too strong for the plant. Fertilizer burn will cause the leaves of the plant to turn yellow or brown and may eventually kill the plant. To avoid fertilizer burn, be sure to follow the instructions on your fertilizer label and start with a small amount of fertilizer before increasing the amount as needed.

The Growth Stages of a Cannabis Plant

Starting off with strong, healthy cannabis seedlings is crucial for the later stages of your plant’s growth. But when do you start fertilizing them? It’s important to understand the different growth stages of a cannabis plant so that you can give them the nutrients they need at the right time.

The Vegetative Stage

After your cannabis seedlings have finished the germination stage and grown their first set of “true” leaves, they will enter the vegetative stage.

This is when your plants will start to rapidly grow in height. The length of the vegetative stage will depend on several factors, such as the type of cannabis strain you are growing, whether you are growing cannabis indoors or outdoors, and whether you are using a natural light cycle or artificial light cycle.

In general, cannabis plants grown under artificial light will have a shorter vegetative stage than those grown under natural light. This is because growers can control the length of the light cycle (usually 18-24 hours of light per day) during the vegetative stage.

Cannabis plants usually remain in the vegetative stage for 4-8 weeks before being switched to a 12-hour light cycle, which triggers the flowering stage. However, some growers choose to keep their plants in the vegetative stage for much longer periods of time (months or even years) in order to achieve very large plants.

During the vegetative stage, it is important to fertilize your plants regularly with a nutrient-rich fertilizer. Cannabis plants are heavy feeders and will consume a lot of nutrients during this phase of growth. If you are growing hydroponically, make sure to check the nutrient levels in your reservoir frequently and adjust as needed. If you are growing in soil, make sure to water your plants regularly so that they do not become dehydrated.

The Flowering Stage

After the vegetative stage, your cannabis will enter the flowering stage. This usually happens when you reduce the amount of light your plant gets to 12 hours per day (“12/12” in grower lingo). Some growers will use a method called “forced flowering” to make their plants flower sooner, but this isn’t necessary.

The flowering stage is when your cannabis plant starts growing buds. This is the most important time to start fertilizing with a bloom fertilizer that’s high in phosphorus and potassium.

Cannabis plants typically spend 6-8 weeks in the flowering stage, but this can vary depending on the strain. When your plants are about 2 weeks away from being done flowering, stop feeding them nitrogen-rich fertilizer. This will help prevent excessive vegetative growth and encourage bud development.

When to Start Fertilizing Cannabis Seedlings

Cannabis seedlings need to be fertilized as soon as they are big enough to handle fertilizer. You can start fertilizing cannabis seedlings with a half-strength fertilizer when they are a few inches tall. If you start fertilizing cannabis seedlings too early, they may be stunted.

Starting Fertilization During the Vegetative Stage

Fertilizing during the vegetative stage is important for the development of strong roots and robust growth. The best time to start fertilizing cannabis seedlings is when they are about 2-4 weeks old and have developed their first set of true leaves.

To fertlize, mix a nutrient solution at half the recommended strength and water the seedlings with it. Once they are established, you can gradually increase the strength of the solution until you are using it at full strength. Be sure to flush the soil with plain water every 2-3 weeks to prevent salt buildup.

Starting Fertilization During the Flowering Stage

As your cannabis plants enter the flowering stage, you will need to start fertilizing them with a different fertilizer than you used during the vegetative stage. Nitrogen is no longer needed in large amounts, and phosphorus and potassium are needed in larger amounts. You should also start using a fertilizer with a lower nitrogen content and a higher phosphorus and potassium content.


The bottom line is, when to start fertilizing your cannabis seedlings is a bit of a gray area. It really depends on the grower’s preference and experiences. Some growers prefer to wait until their seedlings are a few weeks old before fertilizing, while others like to start fertilizing as soon as the seedlings have their first set of true leaves. If you’re new to growing cannabis, it’s probably best to err on the side of caution and wait a few weeks before fertilizing your seedlings. This will give them time to adjust to their new environment and grow a strong root system before you start adding nutrients.

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