How Do I Determine When to Begin Sowing My Plant Seeds
It depends upon how much time you have to care for seedlings before they are tranplanted into permanent spots in the garden.
If you are growing garden annuals that you want blooming as soon as they go into the ground they need to be started indoors several weeks ahead of your planting date. Seed packets will offer germination information to guide you...keep in mind that the information on the back of the packet is based upon ideal circumstances.
Most garden perennials do not bloom their first year from seed so they can be started anytime. Starting indoors will require care to prevent damp-off and repotting if felt necessary. Outdoor germination you will need to protect the soil from desiccation by wind and sun, the seedlings should also be protected from slugs or snails, if a hail storm is coming you can help protect young direct-sown seedlings by turning an old laundry basket over them for the duration of the storm.
Direct-sown seedlings are often a tasty treat for birds and bunnies. A scarecrow and fencing can help protect the seedlings from critter damage, however a starving animal will ignore devices used to deter or scare them away.
Vegetable packets offer a "days to maturity" guideline to suggest when to sow your seeds. Those days are generally based upon how long it takes to grow the first ripe produce after a seedling is about four inches high, those dates are not indicative of how many days needed to produce ripe fruit after germination.
Germination requirements can vary from species to species, though some plant families may have similar requirements. If you have no seed packet to read for germination requirements then you can look up the information on the internet by typing in the plant name + germination. The information may also be found in books at the library.
Winter Sowing, done outdoors, goes on all throughout winter. See the Winter Sowing Forum FAQs for information. There is also forum with FAQs for Starting Seeds Under Lights.