Maybe contrary to your notion of a timeline for seed sowing, fall is the best and perfect time to sow seeds of winter annuals and biennials. This exercise is for the outdoor garden where shortening days, cool rains, and falling temperatures will invigorate them.
Even if the seed fell in early summer, the tiny seed brain waits for an alignment of conditions, the trifecta of circumstances to begin growth. No amount of cajoling will alter their internal clock and when one seed sprouts, others quickly follow.
In my garden, this became evident with Orlaya Grandiflora, a member of the carrot/parsley family. The flowers and plant passed in the heat of summer and no amount of water or sunlight would convince the seed to sprout. An October day changed everything and now I have more seedlings than I can count.
Larkspur is another that is best sown in the fall. At first, they are little more than green dots. It will be early spring before they build bulk and begin their upward trajectory. Flowers arrive in May and early June, extending ornament beyond the flouncy mid-May bloomers, blending with early lilies.
Mullien, clary sage, and hollyhock are a few others that are best tossed out as a seed in fall rather than spring. Throwing them on bare soil is recommended, these are seeds that prefer sunlight to germinate, any open space in the garden will do. All three are biennials, growing foliage the first year and flowering the second only to die in a shower of seed that populates the soil and waits for the cool of fall to sprout.
Winter provides the chilling hours for a perennial seed to sprout as well. Leftover packets or collections of seeds that include perennials should be planted in the fall. A simple way to remember the depth to plant any seed is three times their size deep. Smallest seeds are surface sown.
Moisture aided by freezing temperatures activate the seed, this entire design evolved to keep seeds from sprouting at the wrong time of year. Ticking of the clock or counting days of 35 degrees comes standard with most perennial seed. Spring sowing will often result in little to no germination as essential requirements have not been met. It may take another year before you see any activity.
As the gardens decline in fall and growing seasons come to a close, a cycle of renewal is just beginning. The gardener may be done with the chores of garden upkeep, but a little seed tossing requires the smallest amount of physical exertion. Come spring you will be grateful that full advantage was taken of a chilly winter.