Last time we talked about the minimum soil temperature for germinating many spring plants, now lets look at the maximum temperature for the same plants.
Fava beans will germinate until the soil reaches about 65 degrees Fahrenheit.
By 70 degrees Fahrenheit, arugula, celery, celeriac and mache will stop germinating.
The following vegetables will need to be sown by the time that the soil temperature reaches 75 degrees Fahrenheit: beets, broccoli, brussels sprouts, cabbage, cauliflower, Chinese cabbage, kale, kohlrabi, mustard, onions, parsnips, peas, romanesco, rutabaga, snow peas, spinach, sugar snaps, swiss chard and turnips.
When the soil reaches 80 degrees Fahrenheit, it will be a challenge to germinate lettuce and radishes.
Carrots, leeks, shallots will germinate until the ground reaches 85 degrees Fahrenheit.