Nico’s Nuggets: Getting Seedlings & Clones Started Right The First Time

Hello Nico! I am need of information on seedlings. Can you please give me some data on how warm it needs to be for seedlings? When can I introduce them to my hotter lamps? Any other tips for a beginner? Many thanks for all you do! — Angie R. via the mailbag at

Howdy, Angie. Thanks for reading and writing in with a question!

The infancy stage for cannabis plants, such as seedlings or new cuttings, is crucial for a plant’s development. Starting them off on the right foot helps ensure a healthy life for each plant as it grows and develops towards its flowering and harvest stages.

Whether you are propagating from seed or starting clones from cuttings, there are a few simple tricks to help ensure good rooting and robust growth. Good root structure and preventing young seedlings and clones from stretching are the keys to strong plant development. Root mass will directly correlate to the growth and overall size of your plants.

To start, keeping the root zone temperature around 80°F is essential for rooting plants. Warmer temps between 78° – 82°F will result in faster rooting. Heat mats are excellent sources of heat and can aid in keeping temperatures consistent during colder months.

Next, deploying a humidor tray and dome system will also go a long way in helping plants develop strong root systems. Humidity ranging between 68 – 72 percent is perfect for seedlings and clones trying to root.

nico's nuggets, rooting
These cuttings are rooting in humidor tray and dome systems.

Additionally, a small amount of rooting hormone at the base of the cutting or inside your seed plugs can also help a great deal. There should be no need to use nutrients in your medium at this stage. Once root tips start to protrude from the plugs or medium, the seedlings will be ready to transplant into a larger container and grow medium. At that point, a very mild nutrient solution may be applied. Be sure to measure the pH of your runoff, keeping pH levels between 5.2 – 5.8 for rooting cells for maximum nutrient uptake and less risk of root burn.

Light cycles are also extremely important for seedlings and clones. Cool running light sources, such as fluorescent lamps, are ideal because you can keep them closer to the plants without risk of overheating. Keeping lamps closer to the young plants will help prevent them from stretching and will promote more robust growth. Fluorescent lamps also are heavier in the blue spectrum, which keep internode lengths shorter and prevent plants from stretching.

Nico's Nuggets, seedlings
These seedlings are propagating under banks of T5 fluorescent bulbs.

Next, it is very important to remember that roots breath in oxygen, not CO2, and they do so at nighttime. The dark cycle is critical for rooting plants because this is the time when leaves and stems also transfer energy down to the root zone. Roots grow mostly during the dark cycle, so having 6 – 8 hours of dark in every 24-hour period is strongly recommended. Once your plants are rooted and transplanted into larger containers and stronger grow medium, you can move them under your HID lighting.

Nico's nuggets, roots
Roots are protruding from a slab of Rockwool plugs. In another 5 days these clones are ready for transplanting.

Remember, though, they are still babies and will need to have the lights a bit higher and the temperature a bit lower than usual as young plants can go into shock after transplanting if not done properly. Keep your light cycle at 18-on and 6-off, and keep the temps around 74° – 76°F for another week, before getting it down to 72°F and 40 percent humidity.

Thanks for reading everyone and remember: Grow… And help the world grow, too!

Follow Nico on Social Media: @Nico_Escondido (Twitter) & @Nico_High_Times (Instagram)

Got questions? Email ‘em over to Nico at and be sure to put “Nico’s Nuggets” in the subject line! (Tip: Before sending a question, try the new Search feature on the HIGH TIMES website. Simply click the “magnifier” icon at the top right and type “Nico + your subject topic” to see if your question has already been answered!)

  1. So much misinformation. Hightimes come back when you’ve got roots at day 5. I bet it takes you 7-11 days compared to my 5 days and guess what? My lights are on 24/7. You don’t need any dark time. That is a myth. You don’t need to ph the water either. Grab some rockwool cubes, soak them in a gallon of Reverse Osmosis water with voodoo juice and cal mag plus. dip your clone into some cloning gel and pop it into the cube. Throw that thing into your humidity dome with seedling heat mat underneath set to just under 85F. Leave your light on 24/7 and magically 5 days later you will see roots sticking out the bottom of the rockwool cubes. You should have about an inch of water in the bottom of your tray also. Do not spray the clones with any water. Just leave them alone for 5 days. Once or twice a day you can open the dome and look at them/let some fresh air in. Keep the vents on your dome completely closed too.

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