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The ideal greenhouse temperature for spring seedlings

I'm growing a range of annuals and veg - and all seem to have very different needs for germination and growing on.  I have a small greenhouse that I'm heating with a simple Dimplex termostat controlled heater.  I can now keep temperature steadier over night (around 6C) but it fluxtuates wildly during the day (between 6C and 26C) depending on sunlight.  I've invested in a simple vent opener which I'm going to fix at the weekend - but meanwhile, does anyone have any tips on a good range of temperature to aim for.  I guess that ideally I'd have several greenhouses but like most people I dont have the space or budget for that! 


  • I always used to keep mine at 5 or 6,opening the vents during the day,also the door ( but had a piece of stiff wire to fit in the doorway in case the cats got in) as you say,it has to be one size fits all!! 😁
    The whole truth is an instrument that can only be played by an expert.
  • PosyPosy Posts: 3,601

    It's really difficult. You keep them warm at night then the sun comes out and fries them. If you are at home in the day you can nip out and shade them with some netting and open doors and vents when the temperature rises but it is more difficult if you are out all day. I watch the forecast like a hawk and at least put up some netting if it's likely to get hot while I am out. In a few weeks I will put up proper shading.

    If you have the money, you can buy and fit automatically opening vents and a heater which blows cold air if it gets hot, but most of us have to muddle through. Put your delicate seeds where bigger plants will give some shade and make sure they have water.

  • Thank you Posy and Cagzo.  The auto vent is now fitted and works a treat.  Shading will be my next project.  I think I may invest in a heated propagator to give the heat lovers an extra boost.  
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