If you want to get your vegetable garden off to a fast start, you need to plant your seeds in soil that's warm enough to ensure good germination.
For each type of seed – beans, carrots, lettuce – there is a range of temperatures at which that particular type of seed will germinate (see the chart at right). Beans, for example, will only germinate if the soil temperature is above 60 degrees F and no warmer than 95 degrees F.
There is also an “optimum temperature” at which seeds germinate most readily. In the case of beans, that optimum germination temperature is 80 degrees F. In a perfect world, you would wait for the soil in your garden to be 80 degrees F before planting your beans. At that temperature, you could expect nearly every seed to germinate.
But when spring comes, we are eager to get our gardens planted, and we don’t want to wait around until midsummer to plant beans. In cold climates, the soil temperature in our gardens may never reach 80 degrees, and even if it did, by that time the crops wouldn’t have a chance to mature before frost. Hot-climate gardeners need to get their crops planted early so they will mature before the heat of midsummer.