Soil Temperature Influences When to Plant
As gardeners we are always watching the weather and checking the calendar to estimate the best time to plant. We often overlook a critical factor, soil temperature, when making our plans.
Invest in a soil thermometer and start tracking soil temperatures before planting seeds, transplants and bulbs. Measure the soil temperature at about 4 to 6 inches deep.
Cool season crops like lettuce, kale, spinach, radishes, beets and peas can be planted when the soil is in the 40’s or warmer. Warm season vegetables like tomatoes, peppers, and squash do best when the soil is warmer, from 55 to 60 degrees or more, depending on the plant.
Colorado State University’s Vegetable Planting Guide lists the minimum, maximum and optimum planting temperatures for most of the commonly grown vegetables.
A bit more information: Planting when the soil temperatures are optimum will speed seed germination and reduce transplant shock. Plants placed in the garden when the temperatures are ideal can reduce the time between planting and harvest.