A check of soil temperatures today showed 41 degrees F. That’s warm enough to seed cool season crops such as lettuce, onions, peas, radishes, spinach, cabbage, broccoli and kale in an open garden. (Those using coldframes could beat this planting date by a month or more.)
Soil temperatures should be measured at 4 inches deep at 8:00 a.m. If you don’t have a soil thermometer, you can follow the on-line readings taken at the weather station on the Fort Collins campus of Colorado State University.
Once seeded, you may want to cover with a germination blanket (photo above) to keep small seeds moist until seedlings emerge and even for a week or so afterwards. Our sun, wind and dry air at mile high elevation rapidly dry the surface of soil. This material, anchored with soil at the edges or U pins of bent wire punched through the fabric, helps the surface stay moist. It’s sold as floating row cover or seed germinating fabric at garden centers.
Even with a fabric cover and cool temperatures, at least daily watering likely will be necessary during the days to germination period generally listed on the seed package. In addition to proper planting depth (avoid seed burial deeper than recommended), maintaining consistent moisture is the biggest factor in successful seed germination.
Photo credit: Using seed germination blanket, Carl Wilson