The variable is application rate; the number of pounds of seed per acre; which distinguishes a nice lawn from a weed-filled disaster. This knowledge will help keep your seeds at the right density. You want them to be neither so sparse that nothing grows nor so dense that they overcrowd and compete with one another. It’s what keeps your seeds from turning into a sad, patchy lawn.
This often happens when someone feel they must spread every last granule of seed in the bag, thinking that more is better. That’s not instinctive; it’s bad form. This chart (above) breaks the numbers down by grass type, and as you can see, there’s no one number for everything.
How Much Seed to Use for Your Lawn
High-volume cool-season grasses like perennial ryegrass and tall fescue need lots of leaf cover to smother out weeds. When starting from scratch, you’ll notice the rates inching up into the six- to nine-pound-per-acre range with these guys. These are different than Kentucky bluegrass, though. It spreads through underground rhizomes which explains why you don’t really use that much seed at first. It starts slow and take its time to fill in. That’s where people go astray here; because it seems like all bluegrass wants is to be seated immediately. But it’s more like a vine that has to have some space to stretch out. Too many bluegrass seeds lead to a jumbled mess where nothing competes for space until after it are established.
If you’re dealing with bahiagrass or centipedegrass in the south, then the story’s different, and involves a much finer variety of seed: the kind that’s more like dust than those chunky pellets of fescue. The little guys require less seed, too, like just a few ounce (rather than pounds) to do a surprisingly large area. And if you over-seed your warm-season lawn, you’ll see why poor germination happens, as there will be so many seeds on the surface of the soil that they simply can’t push through. The visual comparison in the infographic shows a lot. It shows how little you really need of things like centipedegrass compared to all the weight required with an erosion control mix or annual ryegrass. It isn’t about strength, it’s about seed size and geometry.
The choice of which species to use also depends on context. For example, if you prepare the ground and plant seeds carefully, you can use the lower end of the recommended range because each seed has a good chance of landing in a good spot. But if you’re casting about on rough terrain, or over established lawn, take into account losses: Some get washed into the gutters by rain, others blow away in the wind and some are snatched up by birds. That’s why when broadcasting, you often need to increase the rate by twenty-five to fifty percent. A lot? Not really. It is just insurance against what happens out there in the world of agriculture. You don’t pay for seed that falls on the flower bed; you pay for seed that falls onto the first inch of your soil.
Timing is also involved, and it is sometimes more important than the actual weight listed on the bag. If planting in fall, for instance, cool-season types prefer their soil cool; they like the ground warmed up enough by then to prompt action but they don’t like it cooking, because weeds start to grow more slowly. Warm-season types are waiting for some late-spring heat to jump-start them. Sowing outside of the best time means planting under less-than-ideal conditions. You have to plant more to make up for poor germination. This takes us right back to square one.
No guessing games, please. Use a calibrated spreader and the correct rate for your particular grass. If you follow the math, you’ll end up with a lawn that looks green on top and feels solid to the touch. It all begins with respecting the math even if it feels tedious at first.