How to take care of Cannabis Seedlings

How to take care of Cannabis Seedlings

Updated: May 24, 2018


A recently germinated cannabis seedling.

Planting Germinated Seeds


To learn how to germinate your seeds, check out Germinating Cannabis Seeds.


Once the cannabis seeds are germinated and the shoots have emerged from the shell, it’s planting time! Timing is critical at this stage. Don’t make the seedlings work around your schedule.

  • Immediately move germinated seeds to light so photosynthesis can begin.

  • Provide gentle air movement with an oscillating fan. This ensures strong stems and hardens the seedlings.

  • Under or over-watering can quickly kill a tender young plant.

The Right Lighting At The Right Time


Give seedlings light to grow once they germinate and emerge from the starter cube. Set your timer for 18+ hours a day and use cool rated fluorescent bulbs. We like T5 fluorescent light fixtures with 6500 kelvin “cool” veg bulbs, positioned about 6-12 inches above the canopy of the plants. Fluorescent bulbs are perfect for seedlings because their gentle light promotes lateral branching, tight inter-node spacing and ideal growth structure. If you use natural sunlight, start in the shade and transition to direct sun over the course of several days.


Young seedlings need fluorescent lighting because they lack roots and are not yet hardened to their environment. High Intensity Discharge lights are too intense for young seedlings—save them for later. Even fluorescent lighting can damage seedlings if the bulb is too close to the plant canopy. Raising lights too high, though, will create skinny, lanky seedlings that struggle to support their own weight. Keep a close eye on your plants to determine the best light placement.


Air Movement Creates Strong Plants


Air movement is essential for encouraging strong stem growth; however, don’t overdo it with young seedlings. Position an oscillating fan on low, pointing at the plants from several feet away. Each day move the fan closer and increase speed until the seedlings “dance” in the breeze. The veg room should also have an air exhaust and intake fan to provide a continuous supply of fresh air to the entire grow room. Outdoors, it is important to provide some shelter from strong wind and weather.


Temperature and Humidity for Healthy Plants


The environment in the veg room is best when it is consistently between 70°-75°F and 30-50% humidity. Cannabis will tolerate conditions outside of these parameters, but expect increasing mold, pest, root and other performance problems if it is too hot or cold, or overly wet.


Do not overcrowd seedlings, or other plants. Only plant one seed per container and keep plants spaced so that they are never touching or competing for light. Healthy plants grow exponentially so make sure they have room to grow!


Time To Transplant


Increased lighting and air movement also increases plant transpiration and metabolism. Seedlings need more water as they produce roots and leaves. Closely monitor seedlings to determine their watering needs and adjust irrigation accordingly. Transplant the starter cubes when you first see roots emerge—before they are a tangled mess of roots. This enables you to water less frequently and will cause a growth boost as the seedling roots out into its new grow medium. If you haven’t chosen a grow medium and cultivation method, now is the time to do so. You have lots of options, like rockwool, hydroton, coco coir, growstone, aeroponics and soil.


pH and Fertilizer


Only water with plain water for the first 7-10 days, or until you see the second set of leaves emerge. If possible, adjust the pH of all water and nutrient solutions to pH 6.0. A reliable pH meter, pH adjustment solution and calibration fluids are essential tools for the gardener looking to optimize chemistry at all growth stages.


Next week we’ll discuss when and how to start fertilizing your seedlings and understanding the life cycle of cannabis.