What are the best conditions for seedlings?

A small plant sprouting from soil

Read this article to learn about the best conditions for your cannabis seedlings. Learn about optimum temperatures, light exposure, air conditions, and the equipment you’ll need to get the best possible results.

The best conditions for cannabis seedlings are a bright, warm (21-23ºC) and humid environment with moving air.

Propagators are simple to obtain and provide an ideal start for young cannabis plants. A propagator is a plastic tray with a transparent top which holds in humidity and warm air while allowing seedlings to receive light. This an easy way to maintain a good environment for very young seedlings . However, since the cover prevents normal air movement (which is very important as it encourages young plants to grow strong stems), cannabis seedlings should not be kept in a covered propagator for too long.

Once the young plants produce their second or third pair of serrated leaves, or if they grow taller than about 7 cm with only the first pair, the cover of the propagator should be removed. A small oscillating fan on the lowest setting is a good way to give indoor plants the air movement they need, while outdoor plants can start to receive the natural outdoor air movement when they have reached this size.

Graphic illustration of how seedlings should be cared for when planted
After seeds are sown in the growing medium, they can be placed in a propagator for the first couple of weeks.

The simplest form of propagator would be a waterproof box with clear plastic sheeting over the top. The advantage of shop-bought propagators is that they often have built-in heating and/or vents in the cover to allow temperature and humidity regulation. They also usually allow more light to reach the seedlings.

If the seedlings are intended for outdoor growing, the covered propagator should be placed next to a window to give the seedlings light. By the time outdoor seedlings are big enough to have the propagator’s cover removed, the process of acclimatizing them to outdoor conditions can begin (weather allowing).

  • Disclaimer:
    Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.


8 thoughts on “What are the best conditions for seedlings?”

  1. I had bad experiences with lights, they were to strong, now I am looking at wing reflectors which are quite practical and it says they don’t burn the plants (if properly installed ofcourse)

    I am currently looking at the Wing reflektor enforcer medium, any opinions?

    Don’t know what to choose, I’m also thinking about the Bat Cool Tube (125-x-490mm) … I would be glad for any opinions ☺️

  2. MastroAldo70

    Sono al secondo tentativo di avviare la coltivazione, il primo tentativo ha avuto esito negativo, su 5 semi autofiorenti femminilizzati, 1 solo è arrivato quasi alla fine, ma la resina prodotta era poca e non ha fatto in tempo a maturare bene perchè la pianta si è bloccata nella crescita ed è seccata. Ora stò provando con 10 semi naturali, sfida ancora più difficile, tutto sempre indoor, con lampade led di cui 5 con luce rossa e blu, 1 piu grande multispettro usata come “sole” che faccio accendere solo 6 ore al giorno alla metà delle 18 ore di luce, sperando che questo simuli appunto il sole nelle ore centrali del giorno.
    sono a 15 giorni dalla nascita, oggi sono alte circa 10/12 cm e stanno spuntando su quasi tutte la 3a coppia di foglie seghettate. Spero che non si blocchi la crescita, vorrei poi usare dei fertilizzanti naturali, come fondi di caffè, bucce di banana, acqua di fagioli, ma ho paura che questi formino delle muffe, secondo voi devo mischiare nel terreno o appoggiarle sopra al terreno nei bordi del vaso, per non far toccare il busto della pianta ?

    1. Mark - Sensi Seeds

      Buonasera Aldo,

      Grazie per il tuo commento,
      Sembra che le tue piante stiano benissimo!

      In generale, le sostanze solide funzionano meglio se tagliate in piccoli pezzi e scavate nel terreno umido prima di piantare piantine o durante il rinvaso in contenitori più grandi. I liquidi possono essere diluiti con acqua e utilizzati come fertilizzante liquido. Fortunatamente, abbiamo anche un articolo sulla guida per principianti ai fertilizzanti fatti in casa qui! (Scusate, è solo in inglese!)

      Godetevi il blog!


  3. raymond joseph getz 111

    Seems like every grower has their own ideas so much so that I find my ownb pattern which changes with every grow with every plant

  4. I’ve got my Automatic Hindu Kush seedlings in an open fish tank next to a window (uk) .. they Initially grew about 7 cm with one pair of leaves.. but for the past 2 weeks haven’t grown at all.. I’ve now put LED lights on to give more light.. but still no change. This also happened to me last year-they just stopped growing and I had to throw them?! What am I doing wrong? I feel like I’m wasting my money every time I try?

    1. Mark - Sensi Seeds

      Good afternoon A,

      Unfortunately, legal restrictions mean we can’t answer grow-related questions or give grow advice on this blog. However, other readers of this blog will often answer questions like yours.

      Please check out the following articles on our blog which I think you may find of use, and I hope you continue to enjoy the blog!

      The life cycle of cannabis: From seed to harvest

      When can seedlings be put under lights or in the sun
      With best wishes,


    2. Check out Growdiaries if you want a few tips. I was where you are about a year ago, so I completely understand the frustration!! The end goal is totally worth it though so don’t give up!! Think of all those big juicy buds that are far better quality and potency when home growing.

  5. 24 degrees celcius …….RH =85……moving air by oscilating fan.

    are these conditions ok for seed started plants in seedling stage

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    The Sensi Seeds Editorial team has been built throughout our more than 30 years of existence. Our writers and editors include botanists, medical and legal experts as well as renown activists the world over including Lester Grinspoon, Micha Knodt, Robert Connell Clarke, Maurice Veldman, Sebastian Maríncolo, James Burton and Seshata.
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