The right temperature in the seedbed

Good evening. I own a vegetable garden of about 50 square meters and this year, unlike in previous years, I have procured and sown in trays the species of plants recommended by the calendar for the current month (tomatoes, courgettes, peppers, cucumbers, peppers, leeks and other aromatic seeds). I have chosen a suitable soil for sowing but I fear that the future seedlings do not have the sufficient temperature to germinate, as I have placed the trays inside the garage where the temperature usually does not drop below 10 degrees, but at the same time it does not reach 18-20 °, from what I understand, the optimal temperature to have the first shoots, and in which the light, even if present during the day, remains scarce. In any case, I always cover the seedbed with fabric / non-woven fabric, to avoid excessive temperature changes, but I don't think it is enough to achieve my goals. I cannot place them on the terrace because the temperatures would be lower during the night and the temperature range certainly higher. How can I solve the problem? Do I have any chance of getting some results anyway?

P.s. unfortunately I live in the city and I don't have much space at my disposal to build any more effective 'shelters' with the use, perhaps, of manure.


Hi Francesco

Each seed has its ideal temperature at which to germinate and then there is a minimum temperature, below which the plant dies or is damaged even irrevocably. If you want to make a seedbed you have to guarantee a suitable temperature and even in special cases, such as colder nights, you have to make sure that the thermometer does not drop too much. You should therefore keep the seedbed around 20/25 degrees, and in any case never let the temperature go below 15 degrees.

From what you tell me I doubt that you will see seedlings born in the current conditions, you must certainly vary something or wait for the climate to change naturally and the temperatures to be higher.

Heat the seedbed

The first option you have is to heat your seedbed: just buy an electric heating mat to be able to keep some seedlings warm. If you build a closed "box" (but ventilated and illuminated for the hours of the day) it will be easier to keep the heat inside. Once the seeds have germinated, I recommend that the plants do not miss the light, otherwise you will see them spinning.

Alternatively, you could, if the climate of your area (which I do not know) allows it, leave the plants on the terrace during the hot hours of the day to take in light and warmth and shelter them in the home in the evening. Obviously it's challenging because you have to bring the seedlings into the house every day and take them out the next morning.

I hope I have been helpful, a greeting and good crops.

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Matteo Cereda2019-01-24T17: 20: 08 + 01: 00
  1. Lorenzo28 March 2018 at 11:42

    Correct me if I'm wrong, but covering an unheated seedbed when not exposed to the wind is of no use. The seedbed does not produce heat to be retained and therefore will always be in thermal equilibrium with the garage.

  2. Francis10 April 2018 at 8:55

    Hi Matteo, thank you for your timely reply. I followed your advice and exposed the seedbed to the sun by placing it on my terrace, covering it overnight with TNT (which as Lorenzo rightly pointed out, I think is certainly more effective in these circumstances). I was thus able to germinate most of the seeds I had planted (tomatoes, courgettes, cucumbers, leeks, basil…). A greeting,


    • Matteo Cereda10 April 2018 at 10:22

      Hi Francesco, I am very pleased that in the end the seeds have germinated… Hurray!

  3. Pine tree30 December 2019 at 8:55

    good morning Matteo interesting what I read but my problem is another, I would like to place a thermometer
    in the center of the garden to check the temperature daily to get ideas on when to sow and transplant.
    The months are shown in the sowing table, which is interesting, but between the first of the month and the last of the month there is often
    a big difference.
    I would like to know for the purchase and the location of the thermometer, if you can help me with some information.
    Thank you and I greet you warmly
    Pine tree
    P: S: this year I will also follow the lunar calendar.

    • Matteo Cereda2 January 2020 at 8:43

      hello Pino, you are right to look at the temperatures, in fact the tables based on the period are necessarily approximate. These are simplifications. In my opinion you have to choose an outdoor thermometer that is able to memorize the maximum and minimum, so that you also know what temperature it is during the night. In fact it is essential to keep the night minimums under control. You could also consider a humidity detector, the hygrometer often is associated with the thermometer. On the position of the first you will have to do some tests to understand the differences between the various areas. Then choose the point that seems representative to you.

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Video: High-quality seedbed preparation leads to a high-quality seedbed (May 2021).