I am planning to start some seed indoors for next spring season. Since the weather is still a bit cold, I am going to be using a heated bed (actually it's a styrofoam box with some sensors and a heat element to control the temperature quite precisely).

The seeds will germinate on paper towels, and then I will move them to small pots and into an outdoors greenhouse until the minimum daily temperature is about 10-12c/50-55f, then they will be planted on the soil.

The greenhouse is covered with polyethylene plastic, the temperature inside is not controlled or monitored. I haven't checked but I think it stays above 10c degrees.

Wont the seedlings have issues with emerging on a ideal temperature and moving them to an environment that while not cold, it has no temperature control?

My concern is that the seedlings may get shocked and die when moving them to an environment that is colder of where they sprouted. Is not that the growing environment will be so cold that is hazardous for the plant, but the germination box temperature will be almost perfect. So, I don't know if the difference between the two environments will cause issues.

1 Answer 1


Difficult question. You need to gain experience.

Usually heated bed will help to have seedling earlier, but then you will plant outside when temperatures are not too cold. So it is up to you (and your weather and your setup) to find the right moment. To early, and maybe you need to repot seedling inside. To late, and you will gain very little (on earlier harvesting [the reason of heated bed).

My problems: every year we have different weather, so it is much adjusting and thinking, and disappointments.

The issues come on some vegetables (usually on biannual ones), where a cold weather outside could tell the plant it is on second year, so to make seed (and not much leaves).

I think you are doing it correctly, so you are already giving them extra care. Heated -> Outdoor green house -> Outdoor garden. Maybe you can add one step: remove cover on green house the week you will plant on open field, or just move the pot outside green house, maybe near a wall, where they are protected: green houses have higher night temperature, also if you do not heat them (less wind, greenhouse effect [you will have night as all nights were cloudy]).

In open field, do some irrigation, and mulching: it will protect to excessive low temperature. If weather office announce a very cold period (it could happen seldom), put a plastic (better just on night) on your vegetables, to protect from excessive low temperatures.

Note: adaptation period is important also for other reasons (and for other plants): sun burns. Indoor and green houses block much UV (not needed for plant growth). A suddenly change could burn the leaves (and also human skin, for once, we are similar to plants).

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