In many areas, the ground is dry, bone dry. Bone dry ground won’t germinate seed, and it certainly won’t support tender young roots, anything that does germinate will generally die a slow and certain death. You need moisture to grow, it’s about that simple. Fall plants get moisture from rain and occasionally heavy fall dew. Planting brassicas (turnip, kale, rape, mustard greens radishes etc.) and many crop species with fewer than 45 days to grow is a fools errand. You might see some stems and some weak growth but there is little hope of producing any tonnage. Before putting in your seed, be sure to know how long it will take to produce a respectable stand.