Seeding rate is per species, not per bag. Tall fescue goes down at six to eight pounds per thousand square feet for a new lawn; Kentucky bluegrass at two to three. Put fescue rate on bluegrass and you have wasted two thirds of the bag.
New lawn versus overseeding
A bare-ground seeding gets the full rate. Overseeding an existing lawn — one that still has at least half its grass — gets half that, because the established plants are already holding the ground.
Going heavier on an overseed rarely helps. The seed that lands on thatch rather than soil never germinates regardless of how much you put down.
Seed-to-soil contact is what decides it
Seed needs to touch soil. Broadcasting onto an unprepared lawn and hoping is the most common way to waste a bag.
Core aerate or rake first so there are openings for seed to fall into, then drag or roll lightly after spreading. On bare ground, rake the seed in a quarter inch and roll it.
Timing matters more than rate
Cool-season grasses — fescue, bluegrass, rye — go down in late summer to early fall. The soil is still warm enough to germinate and the weeds are slowing down. Spring is the second-best window and a distant second.
Warm-season grasses — bermuda, zoysia, centipede — go down in late spring once soil temperature is reliably above 65°F.
Water is the part people quit on
New seed needs the top inch kept damp — light watering two or three times a day for the first two to three weeks, not one deep soak.
Germination is staggered: rye in five to seven days, fescue in seven to twelve, bluegrass in fourteen to twenty-one. A bluegrass lawn that looks like a failure at day ten is usually just on schedule.
Cool season or warm season
The single most consequential choice is which family of grass suits your climate, and it decides both the species and the time of year to sow.
Cool season grasses — fescues, ryegrasses, Kentucky bluegrass — grow strongly in spring and autumn and go dormant in summer heat. They are sown in late summer or early autumn.
Warm season grasses — bermuda, zoysia, centipede, St Augustine — grow in heat and go brown after frost. They are sown in late spring once the soil is reliably warm.
Sowing the right seed at the wrong time is the most common reason a new lawn fails, ahead of anything to do with rate.
What is actually in the bag
Every bag carries a label listing the species by percentage, the germination rate for each, and the percentages of other crop seed, inert matter and weed seed.
Cheap seed is cheap because of those last three. A bag with two percent inert matter and no weed seed is a different product from one with fifteen percent inert matter, even at the same weight.
The germination percentage matters too. Seed with eighty-five percent germination at a given rate is not the same as seed with sixty percent, and correcting for it is simple arithmetic the bag lets you do.