If your final container size is up to 11l, you have the option to sow seeds directly. This is only a viable option when growing from seed. Clones will not take root in such a large container. Initially, seedlings in large pots will grow more slowly than those in smaller containers. After a few weeks of vegetative growth, the difference is negligible.
An 18-6 light schedule is considered the sweet spot by most growers. White light is preferred. The source of light should be CFL, MH, or LED. If you have a sunny windowsill, it can work in a pinch.
Cannabis seedlings need to be treated delicately. Mind your marijuana like babies. If seedlings need support, prop them up with a toothpick or a cocktail stick and some soft gardening wire.
The right time to transplant your seedlings is just before they outgrow their current container. With cubes, you can see roots poking out telling you it’s time to pot up. When you start with a cup or small pot, you are relying on above-ground cues. Typically, when the set or sets of true leaves of the seedling have spread out to cover the circumference of the container, it’s time. Also, vertical growth will be an obvious indicator.
Finally, gently slide the plant, roots first, into the large container. Replace the lost topsoil or coco with a handful or two over the top and add a little more water. That’s the secret to stress-free transplanting.
Unfortunately, rockwool is a really bad idea for soil growers, even the smaller sized blocks. Invariably, the block retains more water than the surrounding soil. Green, sludge-like algae growth soon becomes a problem. Sure, sometimes you can get away with the tiny cubes, but why take the risk?
Many soil and coco growers use cups or small plastic pots as starter containers, typically, anywhere in size from 0.5–5l. Lightly fertilised soil mixed with perlite or coco coir mixed with 30–50% perlite are the most common blended media for seedlings. So long as the base of the container has plenty of drainage holes and the interior can hold the volume of medium required, it can serve as a starter pot. Don’t be afraid to improvise. Poke a few holes in the base of a paper coffee cup with a pin and it becomes a pot.
Stretchy or floppy seedling growth can be due to genetics. Often, it’s an indication the grow lamp is positioned too far away from the canopy. A cool white 250W CFL can comfortably hang 15cm above a dozen or more seedlings without scorching leaves.
Roots grow in the dark. That’s why we advocate 18-6 or 20-4 over a nonstop 24-hour light cycle. High humidity, ideally around 70% RH, and temperatures in the 20–24°C range make for a perfect seedling habitat. A propagator, thermo-hygrometer, and a spray bottle of water are the tools to help you dial it in.
Transplanting seedlings is a critical stage in the cannabis life cycle. Get your grow off to a great start with our guide to transplanting.