Vegetable seed germination temperatures


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 :

Optimum germination temperatures
o Celsius

Temperature
range
Plant
species
Suggested
target
temperature
0-25 Cabbage lettuce 5 +
0-29 Crisphead lettuce 5 +
10-19 Celeriac
Celery (green)
15
12+ Sweet corn
French bean
Runner bean
15
5-32 Broad bean
Cabbage
Cauliflower
Broccoli / Calabrese
Brussels sprouts
Kale
Peas
Radish
8 +
13 + Courgette
Cucumber (ridge)
Marrow
15 +
15 + Pepper (capsicum) 21
7 + Beetroot
Carrot
Parsnip
Spinach beet
Swede
10 +
7-21 Chinese cabbage
Leek
Onion
12 +
18 + Celery (golden self blanching)
Chilli
Gourd
Squash
21 +
21 + Aubergine
Cucumber (greenhouse)
21-25

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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.

Practical tip

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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