Seedlings or sproutlings are part of the VEGETATIVE PHASE of the cannabis life cycle. The purpose of this period of life is to gain height, foliage & a strong stem to support heavy buds later on. Your plant is like a child at this point & is not sexually or physically mature. It will go through its awkward puberty during Week 5 or 6. But an autoflowering plant remains in "veg" for approximately 3 to 4 weeks regardless of what you do to it. It's on a pre-set time clock, so anything you do to slow its growth will result in a reduced yield at harvest. As a weed, cannabis is pretty resilient overall, but at the seedling stage it's especially vulnerable to things like extreme temperatures, overwatering & predatory bugs or animals.
As soon as your seed sprouts, it's time to get it under a CFL bulb immediately. To be on the safe side, start with the light about 8 inches away from your seedling & only use one bulb to avoid shocking the little one. You can lower it down to within 4 inches from the plant gradually. Place it above--not to the side of--your plant. I made this mistake & almost paid dearly for it. Cannabis likes its light to come from above the same way it grows under the sun in nature. I started with a 14/10 cycle (lights on for 14 hours per day; off for 10) to get the seedling acclimated to the light. This went on for 2 days before switching to 18/6 for another 2 days, then finally settling on 20/4 for the rest of vegetative phase.
|Ridged/serrated leaves = true leaves. Smooth round leaves = cotyledons.|
Autoflowers can grow under a 24-hour light cycle, but my plants seemed to "enjoy" the short dark period each day. Plus it saves on electricity. What you don't want to do is try to grow them under a 12/12 or 14/10 light cycle like a regular photoperiod plant. That's because their lifespan is much shorter & they only have a limited time to gain height & mass. So you'll want to maximize the time they have under the lights each day. But in the first week, it's good to slowly increase light time so they don't fry.
At this point you should be watering thoroughly about twice per week. But the frequency depends on your container size, soil type & other factors, so use this guide instead: water when the soil is dry up to your first knuckle. To test this, stick your index finger in the soil at the outer edge of the container away from the plant so as not to disturb its root system. You should water enough that a little stream comes out the drain holes but not so much you're flushing out the nutrition in the soil. If you want to be super precise with your watering, you can weigh your container on a scale when it's completely dry & write down the weight so you know when it's time to water again. That eliminates the guess work.
I chose to do one of my weekly waterings from the top & the other from the bottom in a tray, where I left the cup for 5 hours each time to soak up its water. I also opted to do "foliar misting" (spraying the leaves with a spray bottle) 3 times per week until my plant's first set of true leaves were large. After each misting, I'd cover the plant with a Ziploc bag for 5 hours to help keep in the humidity. But this is totally optional. Plants in vegetative stage need a relatively high humidity level of 60% or more, particularly when they're just little sprouts.
|Ziploc humidity domes. Apply after misting for a few hours.|
Factors like humidity, heat & light stress can influence the plant's sex in the first 3 weeks of life. If exposed to excessive heat & light along with low humidity or under-watering, it's more likely to come out male or hermie...even if it's a feminized seed. Don't stress over this fact though; aiming for comfortable temperatures of 70-85 degrees Fahrenheit (20 or 30 Celsius) should keep your plant fully female if you have feminized seed.
I consider plants to be out of the seedling stage when they have two sets of fully formed "true leaves" (not cotyledons). But that's a personal thang. It's all vegetative growth in the end. The sprout stage is just extra fragile so I gave it its own little guide. 😊