The practical answer at a glance
- 12 to 15 pounds of pure live seed per acre is the normal drilled target for most U.S. fields.
- Broadcast planting usually needs 10 to 15% more because seed-to-soil contact is weaker.
- Coated seed must be converted from bag weight to pure live seed; 15 lb PLS can mean 17.5 to 24 lb of bagged seed.
- At roughly 200,000 to 220,000 seeds per pound, 12 to 15 lb/ac equals about 2.4 to 3.3 million seeds per acre.
- Roundup Ready helps with weed control, but a shallow, firm seedbed still decides whether the stand sticks.
Start with the acre rate that makes sense
I start with 12 to 15 pounds of pure live seed per acre for a drilled planting in decent conditions. Iowa State University Extension and UMN Extension both land in that same practical band, and I treat it as the normal answer for most Midwest-style hay fields: enough seed to build a productive stand without paying for a pile of plants that will thin out anyway. When the seedbed is rough, late, or broadcast, I move upward. When conditions are excellent, I stay closer to the low end.
| Field situation | Rate to plan for | Why |
|---|---|---|
| Drilled, firm seedbed | 12 to 15 lb PLS/ac | Good seed-to-soil contact usually gives enough plants without wasting seed. |
| Broadcast planting | 13 to 17 lb PLS/ac | Poorer contact reduces germination, so I add 10 to 15%. |
| Late or difficult planting | 15 to 20 lb PLS/ac | Insurance can help when weather or residue threatens emergence. |
That is the part many growers miss: the number on the bag is not the number that matters. The next step is converting the label into actual living seed.
Drilled, broadcast, and coated seed do not use the same math
The bag weight is not the seeding rate. Once seed is coated, inoculated, or carrying less-than-perfect germination, I calculate the pure live seed fraction and then work backward to the number of pounds I need to buy. UMN Extension’s seed-label guidance makes this point very clearly, and it is the easiest way to avoid underseeding a pricey bag.
| Seed label example | Pure live seed | Bagged seed needed for 15 lb PLS/ac | What it means in practice |
|---|---|---|---|
| 90% pure seed, 95% germination, 10% coating | 85.5% | 17.5 lb | A fairly typical coated bag needs noticeably more weight than the target rate. |
| 66% pure seed, 95% germination, 34% coating | 62.7% | 24 lb | Heavy coating can change the acre math fast. |
| 65.8% pure seed, 80% germination | 52.6% | 28.5 lb | Older or weaker seed needs a lot more bag weight to deliver the same live seed count. |
The formula is simple: target PLS divided by the PLS fraction equals pounds to order. If the label is weak, the acre rate has to rise just to deliver the same live seed count.
Roundup Ready changes weed control more than stand density
Roundup Ready alfalfa matters because it gives me more flexibility in the first 60 days, which is exactly when weeds can rob moisture and light from tiny seedlings. That flexibility is useful in fields with patchy weed pressure or a late planting window, and it is one reason some growers feel comfortable staying near the lower end of the normal seeding range. But it is not a magic stand-building trait. In well-managed fields, I have not seen a consistent payoff from pushing seed rates much beyond the normal band just because the crop is glyphosate-tolerant.
- Use the trait to clean up weeds early, not to excuse a poor seedbed.
- Stay honest about field pressure; heavy weeds may justify a little more seed, but not sloppy planting.
- Spend extra attention on the first spray window, because early competition is what thins stands.
- Remember that the economics improve when you buy only the seed you can actually use.
That is why I treat the RR trait as a management tool, not a reason to rewrite the stand target.
How many seeds that means in the ground
If you think in counts instead of pounds, the math gets clearer fast. Alfalfa seed is small, and there are roughly 200,000 to 220,000 seeds in a pound. That means 1 pound per acre is only about 5 seeds per square foot; 12 pounds is about 60 to 66 seeds per square foot, and 15 pounds is about 75 to 82. Most of those seeds will not become permanent plants, which is exactly why the starting number has to be bigger than the final stand.
| Pure live seed rate | Approx. seeds per acre | Approx. seeds per square foot | What it usually means |
|---|---|---|---|
| 12 lb/ac | 2.4 to 2.6 million | 60 to 66 | My normal drilled target in good conditions. |
| 15 lb/ac | 3.0 to 3.3 million | 75 to 82 | A common insurance rate for ordinary fields. |
| 18 lb/ac | 3.6 to 4.0 million | 90 to 99 | Only worth considering when the field is tough or broadcast. |
A stand that finishes the season with roughly 25 to 30 healthy plants per square foot is usually doing fine. The trick is getting enough seedlings through the first month without wasting seed on a rate that the field will thin away anyway.
Planting details that make the rate work
The best acre rate still fails if the seed is buried too deep or dropped into a loose, drying seedbed. I want the soil firm enough that a footprint sinks only about 3/8 to 1/2 inch, and I want the drill set shallow enough that most seed ends up around 1/4 inch deep. On heavier soils I stay at or under 1/2 inch; on lighter soils I still resist the temptation to plant deep just because the surface looks fluffy.
- Target a soil pH around 6.8 to 7.0 before planting.
- Use fresh inoculant if the seed label does not already guarantee it.
- Pack or roll after seeding when broadcast planting leaves seed exposed.
- Control weeds before planting and again quickly after emergence if pressure is high.
- Do not let residue or rough seedbeds force the seed deeper than it should go.
Those basics sound ordinary, but they decide whether the seeding rate turns into a stand or just into expense.
A practical way to order enough seed for one acre
When I turn this into an order sheet, I work from pure live seed first and bag weight second. For a seed lot with 90% pure seed and 95% germination, the PLS fraction is 85.5%, so 15 lb of PLS per acre means about 17.5 lb of bagged seed. If the coating is heavier and the PLS fraction drops to 62.7%, that same acre needs about 24 lb of bagged seed. The label tells you which of those numbers is real.
If I were buying for a 10-acre field, I would simply multiply the adjusted bag weight by 10 and keep a little extra on hand for calibration and odd-shaped ends. That is a better habit than guessing high and hoping the planter somehow fixes the math.
The number I would remember before I place the order
For most U.S. fields, I would plan on 12 to 15 pounds of pure live seed per acre as the working range for Roundup Ready alfalfa. Go higher only when the field is rough, the seed is heavily coated, or broadcast planting leaves you no choice. The rest of the job is simple but unforgiving: shallow placement, a firm seedbed, and early weed control. If those pieces are right, the acre rate takes care of itself.
