Forget about seedling boxes and phytolamps - these flowers will sprout even if you just throw the seeds into the ground.
For example, calendula. Its orange "suns" will not only decorate the flowerbed, but also scare away nematodes. Sow it in April directly into the ground, and in a month the area will sparkle with colors.
Another champion is cornflower. Scatter the seeds along the edge of the beds, and they will sprout even in the stones.

And if you want a vertical accent, plant sweet peas. Their shoots will climb the fence, and the aroma will fill the entire garden.
Don't be afraid to experiment: mix poppy, cosmos and flax seeds, and in a couple of weeks you'll have a wild meadow in the style of Provence.
The main thing is not to bury them too deep. Sprinkle with soil 0.5 cm, water and cover with film until shoots appear.
And remember: annuals like nasturtium or eschscholzia can be sown every 2 weeks - this way flowering will not be interrupted until frost.
After a season, you will understand that seedlings are for weaklings.
But there are nuances. For example, morning glory will only sprout in warm soil - sow it at the end of May. And daisies prefer partial shade: scatter the seeds under an apple tree, and they will bloom like a carpet.
Forget-me-not is suitable for damp areas - its blue flowers love dampness.
And the last life hack: if you mix marigold seeds with sand, it will be easier to distribute them evenly.
In two months, your plot will turn into a paradise for butterflies and bees. And no seedlings!