I have seen some people throw seed without using dirt. Is it less or more efficient ?
Here is this video here that shows what I am talking about
In the video, he applies a soil-based topdressing material after spreading seed on the lawn. I'm not sure where you're getting the "without using dirt" from. If you simply throw grass seed onto compacted soil, you will get poor germination.
I'm not a lawn expert, but if I was going to go to the cost and effort of spreading grass seed on my existing lawn, I would definitely spread a thin layer of finely sifted compost or topsoil over the top of the seed. If you have bare spots, I think it would be worth the effort to scratch these up so that the seeds make good soil contact when they land there.
For what its worth, I conducted an experiment to determine the best way to sow grass seed before reseeding my lawn with $200 worth of KBG seed.
In pot #1, I just sprinkled seed on the dirt. Nothing else.
Pot #2, I sprinkled seed and covered with a light covering of dried grass clippings.
Pot #3, I sprinkled seed and then rubbed my hand overtop lightly to similate "raking in".
Of the 3 pots, and to this day, pot #1 is the densest. Pot #2 has the tallest grass, but not as dense as pot #1. Pot #3 had the poorest germination rate and has the shortest grass. Actually, pot #3 is quite pathetic looking.
It seems the worst way to sow KBG is to cover the seed with dirt. This may be different with a variety having larger seed, but KBG seed is very small and seems to lack the strength to emerge from under the dirt... or maybe the seed rotted in the ground. Its hard to be certain.
The dirt used in the pots is the same dirt as my lawn, which was mixed and sifted, then distributed to the 3 pots. The pots were kept in the same location and were watered by rain, so watering was even between the 3. The soil had a loose texture on the surface and was in no way compacted when the seeds were sown.
Unfortunately, conditions prevented me from just throwing the seed on bare dirt, fearing the seed may dry before germination or the rains would wash it away. It takes a full 7 days before KBG seed sprouts. So, my lawn got the pot #2 treatment since pot #2 had an acceptable appearance and seemed to give the best odds for at least a decent germination rate in unpredictable weather.
I have no regrets and mulching seed lightly with grass clippings seems to be an acceptable way to sow grass seed as this most closely replicates nature where seeds fall to the ground in the thatch between grass blades. Grass seeds in nature are not generally covered with soil.
Grass is resilient and the breeds over the years get stronger and stronger. I feel like they just tell you what the "proper" method is because they want you to buy all the tools needed. If you have a lawn that's half grass and half dirt and not sure what to do, just rake up the dry dirt area, add some compost and mix it in there with the loose dirt you raked up. Start making your own compost if you can, it's easy. Compost is basically just dirt.
Then use your hands to evenly scatter the seeds by clutching the seeds in your palm and shaking your hand side to side letting the seeds sprew out from the sides and fingers. Then water it. The loose dirt compost will turn into moist and muddy and the seeds will sink in. Water it 3 times a day with a hose, just spray it. Again, no need to be accurate. These grass are warriors, centuries of selective breeding.
Don't worry about birds unless there's tons in your area but they can't eat all the seeds in time. Day by day the seeds will dissapear as they wiggle themselves naturally into the soil by wind and slow erosion. If you extra toss some nutrient stuff on the soil as a bonus: toss the grass feed like you're feeding a giant koi pond but make sure you don't overlap too much.
Wait a few weeks, bingo bongo. Grass is grown and they start regulating themselves.
Soil test? Eh, sounds annoying. Dry soil just needs moisture and nutrients - that's where the compost comes in.
Lime powder? Meh.
Seed spreader? A rich person luxury item, just do it by hand. "But the grass will be patchy!" Not really.
If your current lawn is weedy I suggest you apply herbicide. Wait 3 weeks, then plant your grass.