I have built myself a simple heated environment to start growing some plants (in the middle of winter). Reading online I was surprised to see that the optimum temperature for germination of nightshades is around 29 degrees c - a lot higher then I had thought (I previously did it at 20 degrees c) - this got me thinking - does anyone have any insights into if temperature fluctuation is beneficial during germination and if so what the ideals are - also, will germinating at cooler temperatures make for a hardier plant - I can't keep them at that temperature once they start growing !)

  • By nightshades, are you referring to edible solanums such as tomatoes and peppers, or simply ornamental solanums?
    – Bamboo
    Jul 16, 2016 at 12:28
  • Hi davidgo. Would you mind telling us the country you live in? I'm not sure if you meant that it's winter now or that you've built this as a way to plan ahead for when winter comes. It's up to you of course, I don't want to invade your privacy by asking for information you might want to keep private. Thanks! Jul 16, 2016 at 14:26
  • Night temperatures this month about 8 deg C, and lowest 2 deg C. Really strange winter this year. Jul 16, 2016 at 18:47
  • Edible Nightshades - tomatos, capsicums and eggplants (and cucumbers, Zucchini). I live in rural Auckland, NZ (so 6 degrees c colder then akl on cold nights). I expect the plants will need to fend for themselves in a (currently unheated) unheated polytunnel in September. We have had sub-zero temps here - I recorded -2.5c as coldest to date.
    – davidgo
    Jul 16, 2016 at 20:39
  • NO, davidgo! Temperature fluctuations are not at all good for germination or growing plants. Anything below 50 (sporadically) and above 85 degrees F., sets plants and fruiting backwards. Germinating is critical to keep the soil and air temperatures as even as possible. And to expect plants to 'pull up their bootstraps, get tough' even with a polytunnel will definitely be a negative experience!! Plants are NOT ANIMALS. They don't have the same survival mechanisms as animals/humans are relegated. How long have you been growing in this polytunnel? How long have you been growing vegeys?
    – stormy
    Jul 16, 2016 at 21:44

1 Answer 1


For specific germination instructions, you'll have to be more specific on plant type.

From the wiki: The family ranges from annual and perennial herbs to vines, lianas, epiphytes, shrubs, and trees, and includes a number of important agricultural crops, medicinal plants, spices, weeds, and ornamentals.

Two pieces of unsolicited advice on starting plants in winter:

  1. Don't start too early.
  2. Don't worry too much about root bind (You'll tease the roots (or cut off the bottom half inch) when you plant outside anyway.

As far as making a hardier plant through exposure - generally you don't want to do that to indoor seedlings. As an indoors seedling, the developing root ball is more exposed to the elements than it ever is when the plant sprouts naturally.

Naturally: the soil around the root ball insulates it from temporary, drastic fluctuations in air temperature.

Indoors: the root ball is surrounded by air and has very little insulation.

Grow a strong seedling with ideal conditions, then transplant outside after the last frost. A healthy root ball can weather the weather, and guide the plant to grow to suit conditions.

Depending on the type of Nightshade, there may be some winterizing to do when late autumn comes around. I'm curious as to the species because of the high germination temperature. Is it an edible that germinates through digestion, vine that doesn't sprout until late spring and sleep/creep/leaps - must know.

  • I regret that its too late not to start to early! Lots of different nightshades - Ping Tung eggplant, Black Beauty Eggplant, Zebra Eggplant, Cocktail Tomatos, Regular (hybrid) Tomatos, Baby Bell peppers, Goji Berries + Black Beauty Zucchini and some type of Cucumber!
    – davidgo
    Jul 16, 2016 at 20:45

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