"In the morning sow thy seed," according to Ecclesiastes, and it is not bad advice for gardeners. Morning planting offers a seed more of what it needs to germinate and fewer dangers.
Seeds need warmth to germinate--temperatures between 65 and 75 degrees--and sunlight works best. Seeds thrive on about 12 to 16 hours of sun each day. Only morning planting will allow seeds immediate substantial sunlight exposure.
If you plant seeds in the morning, you can give them moisture throughout their first 12 hours in the garden bed. A constant level of humidity is important to seeds; they are very sensitive to lack of water. Morning planting also will delay exposure to rodents.
Seeds and plants grow in spurts at night, not during the day. Charles Darwin was the first to report this finding, over a century ago. Plants use their daylight hours to focus on other matters, such as the photosynthesis that produces its energy.