On the whole, I don’t do much seed starting by sowing directly in the ground. Granted, there are some situations where I’ve had fine results:
My main problem with direct sowing is the lack of control, which leads to wasted seeds. It’s almost inevitable that some seedlings will get lost to slugs, rabbits, and other pests, or to extreme weather conditions, like pounding rain or dry spells. If they do make it through all that, then that are left need to be thinned out. It may be possible to move some crowded seedlings to another spot, but mostly, I find I end up with a lot of seedlings in one spot and few where I really want them.
Weeds are another issue when direct-sowing. Weed seeds already in the soil typically germinate much more quickly than the seeds we plant, and they can easily crowd out more delicate seedlings. It can also be very difficult to tell the weeds from the “good” seedlings. I can’t tell you how many times I have pulled out precious seedlings by accident! You can sometimes find photos of what a given plant’s seedlings look like (I’ve been adding them to my Hayefield listings as time allows), but beware: weeds have a sneaky way of impersonating more desirable plants. (Just try pulling weedy grasses out of ornamental grass seedlings and you will know what I mean.)
One common mistake I find some novice seed-sowers making is thinking that they can scatter a packet of seeds over an existing planting (like the one above) or even a weedy or grassy area and expect the seeds to sprout and thrive. Generally, the advice to “scatter,” “direct sow,” or “sow directly in your garden” presupposes that you have a prepared seedbed (as below, for example), where the soil is already loose and free of weeds, and where you can easily monitor the progress of the sprouting, water frequently to keep the soil moist, and thin out the seedlings as necessary.
Even then, I consider direct-sowing a gamble when starting with a single packet of seeds, particularly if they are very small. It can be ok if you have a LOT of seeds from plants you already have growing: go ahead and shake out the dried seedpods of annual poppies, annual larkspur, white lace flower (Orlaya grandiflora), Brazilian vervain (Verbena bonariensis), or flowering tobacco (Nicotiana) over your borders in late summer or fall if you hope to have them pop up here and there among existing perennials next year. But don’t fling a packet of 50 tiny poppy seeds over a flower bed and expect them to fill the area with a spectacular show of blooms.
When I am starting with a small amount of very special and/or small seeds that need direct sowing, I find it much better to plant them in a small “nursery bed” I keep just for this purpose: a small raised bed filled with a mix of topsoil and compost. If I run out of space there, I will set aside part of a vegetable-garden bed for direct-sowing special flower seeds. I let them grow and flower there and then collect the seeds, so I have a much larger number of seeds to work with the next year and can risk losing some if I direct-sow in less-than-perfect spots.