Humidity should also be in central focus early on in the plant’s life cycle. It is crucial to maintain the appropriate humidity throughout the entire growing process because humidity affects the rate at which your crops will transpire. Cannabis plants will always try and maintain a equilibrium when it comes to the water levels inside and outside the plant. So if the humidity in the grow room is too low the plant will begin to transpire dangerously quick and lose its necessary nutrients. New stunted leaves, dying flowers, and older shriveling leaves are all indications of rapid transpiration. In the seedling stage, humidity needs to be at its highest levels.
I would recommend aiming for 70% and decreasing by around 5-10% each week until reaching the 40% mark. Until the plant has fully developed roots, lower levels of humidity in the air will cause stunted growth. It’s important to understand that levels above 45% are usually dangerous and unwanted in a grow room because they can cause mold and mildew in mature plants. It’s often hard to reach 70% humidity for your seedlings without the help of humidity domes or using a humidifier.
Another important determination to make is when to begin adding nutrients to the plant. I would say that it should be right around the same time you set up the fan and begin building its root structure. Up until the point where it shows its first set of leaves you should be fine using plain water that has been PH’d correctly. When you do begin adding nutrients, remember less is more and that the last thing you want to do is cause nutrient overload this early on. General Hydroponics brand has a chart that includes the appropriate amounts for the different stages of growth, including the seedling stage. I would use this as a guide more than a precise measurement. They often overstate the amount of nutrients you need in order to sell their product more quickly. I would also start smaller than the recommendations for other brands too until you know exactly how your plant will react.
The last important thing a grower should monitor is the space between the light and the top set of leaves. During this stage, I would highly recommend only using compact fluorescent lighting due to the intensity of other lighting sources. Just like with high winds, high voltage lighting can cause irreversible damage that the plant may never recover from. Even with CFLs, not maintaining the right distance can cause similar problems.
The ideal height should only be 2-4 inches above the highest point of the plant. Any higher than that, and you’ll likely see it begin to stretch into a skinny long stem. These lights still emit heat and if they are really close will cause leaves to wither and dry up. Make sure to check the height at least once a day and make adjustments as needed. Maintaining the perfect environment early on always pays off and leads to a strong support system capable of holding the densest of buds.