Seeds of different vegetable species germinate at different temperatures.
Some do not like it too hot, some too cold and some neither too hot nor too cold.
Try to germinate seeds at the optimum temperature as shown in the table below.
Some of the problems with germination temperatures which are too hot or too cold are :
- slow germination leading to attack by fungal diseases
- eratic germination giving plants of different ages
- plants are not ready for planting out when wanted
- crop sequencing and continuity get out of sync'
|0-25 °||Cabbage lettuce||5 ° +|
|0-29 °||Crisphead lettuce||5 ° +|
|12+ °||Sweet corn
|5-32 °||Broad bean
Broccoli / Calabrese
|8 ° +|
|13 ° +||Courgette
|15 ° +|
|15 ° +||Pepper (capsicum)||21 °|
|7 ° +||Beetroot
|10 ° +|
|7-21 °||Chinese cabbage
|12 ° +|
|18 ° +||Celery (golden self blanching)
|21 ° +|
|21 ° +||Aubergine
E-mail me with any additions to the list :
Germinating seeds under cover and transplanting is, of course, the easiest way to raise temperatures, but it can be more difficult to keep soil temperatures down for seeds sown during the height of summer.
Providing shade and regular watering with cool water are simple means of keeping the soil temperature down for crops most at risk such as Japanese onions and cabbage lettuce.
Research has shown that sowing between 2pm and 4pm gives better emergence than sowing in the morning or early evening. This is because the temperature sensitive phase of the germination process is completed at night when soil temperatures are lower.
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