Hot summers, windy fronts, and sudden fall cold snaps. That’s normal life in Oklahoma.
Your Bermuda grass feels every bit of it.
So here’s the big question:
Should you apply potassium and phosphorus to Bermuda grass in the fall in Oklahoma?
The short answer is yes for potassium, and maybe for phosphorus.
Potassium helps your lawn handle winter stress and green up faster in spring.
Phosphorus only helps if your soil is low or if you’re laying new sod or seed.
This guide breaks down when to apply, how much to use, which products to pick, and what kind of results you can expect in Oklahoma yards.
Quick Answer for Busy Homeowners
Potassium: Yes, for most established Bermuda lawns.
Phosphorus: Only if your soil test shows you need it or if you’re planting new turf.
Fall in Oklahoma is wild—warm days, dry air, and sudden freezes.
Feeding your lawn with the right nutrients now helps it stay strong and recover faster when spring returns.
Why Fall Potassium Matters for Bermuda in Oklahoma
Potassium is the “winter strength” nutrient. It helps your grass store energy, move water, and protect cell walls when temps jump from 80 to 30 in a day.
You might not see potassium at work, but you’ll see the results:
- Fewer winter-killed patches in spring
- Faster green-up
- Better drought tolerance
- Less disease during cool, damp nights
Think of potassium as your lawn’s winter coat. You’re not pushing growth right now—you’re helping the turf toughen up and survive the cold.
When Phosphorus Helps (and When It Doesn’t)
Phosphorus builds roots. It’s great when you’re planting new sod or seed, or if your soil test shows low levels.
But many Oklahoma lawns already have enough.
Adding more won’t make your grass greener—it just runs off into creeks and ponds during rain.
Also, high soil pH (common in Oklahoma) can lock up phosphorus, keeping plants from using it. That’s why a soil test is key.
And always, keep fertilizer off sidewalks, driveways, and near drains or ditches.
Times to Skip Potassium or Phosphorus
- Skip phosphorus if you don’t have a soil test.
- Don’t fertilize before heavy rain.
- Don’t apply on frozen soil.
- Avoid high nitrogen late in fall.
- If the grass is fully dormant and soil temps are below 50°F, wait for spring.
When and How to Apply Fertilizer in Oklahoma
Keep your plan simple.
Test your soil, time your fertilizer by soil temperature, and use light, even rates.
Always water after you apply.
Ideal soil temperature: 60–70°F at a depth of 4 inches.
That usually means mid-September to mid-October across most of Oklahoma.
By region:
- Central Oklahoma: Mid-September to early October
- Eastern Oklahoma: Late September to mid-October
- Panhandle and Northwest: Early to mid-September
If your soil test shows low or medium potassium, make one or two light applications spaced 3–4 weeks apart.
If you’re seeding or laying sod, apply any needed phosphorus at that time.
How Much to Apply
Keep the math simple.
Potassium:
Apply 0.5 to 1.0 lb of K₂O per 1,000 sq ft each time.
If your soil test shows low to medium potassium, split it into two smaller apps.
Phosphorus:
Only if your soil test calls for it.
For established turf that tests low, 0.25 to 0.5 lb of P₂O₅ per 1,000 sq ft is typical.
For new sod or seed, you can go up to 1.0 lb P₂O₅ once at planting.
Always follow your soil test and the bag label.
Product Picks That Work in Oklahoma
Easy, reliable products you can find almost anywhere:
For potassium:
- 0-0-60 (Muriate of Potash)
- 0-0-50 (Sulfate of Potash)
For phosphorus:
- 18-46-0 (Diammonium Phosphate or DAP)
- 0-46-0 (Triple Superphosphate)
Use a broadcast spreader.
Calibrate it on a measured driveway area.
Apply half the product going north-south and the other half east-west for even coverage.
If you’re also putting down a fall pre-emergent, only mix products if both labels say it’s safe.
Water In and Wrap Up Right
Water your fertilizer in with about ¼ inch of irrigation right after applying.
Then go back to your normal fall watering schedule.
Sweep or blow any stray granules off hard surfaces.
Keep mower blades sharp and hold your mowing height steady until the grass goes dormant.
Avoid high nitrogen after early September so Bermuda can harden off before the cold hits.
Real Results from Oklahoma Yards
Tulsa Backyard:
6,200 sq ft of Bermuda in full sun. Soil test showed medium potassium, adequate phosphorus.
Applied two rounds of 0-0-60 at 0.5 lb per 1,000 sq ft.
Result: Greened up two weeks earlier than the neighbor’s untreated yard. Fewer thin, brown spots after a cold January.
Oklahoma City Front Lawn:
4,800 sq ft with heavy foot traffic. Soil test low in potassium, adequate phosphorus.
Applied two fall rounds of potassium, no phosphorus.
Result: Thicker canopy and stronger color two weeks into green-up. Less drought stress during a windy April.
Norman New Sod:
3,500 sq ft installed in late September. Soil test low in phosphorus and medium in potassium.
Applied starter fertilizer at install for 0.75 lb P₂O₅ and 0.5 lb K₂O per 1,000 sq ft.
Result: Sod rooted fast, seams stayed tight through winter, and the lawn filled in by April.
Weekend Plan for a Smarter Fall Application
- Check your soil test. No test? Go with potassium only and skip phosphorus.
- Watch soil temps. Target 60–70°F at 4 inches.
- Measure your lawn and calculate product needs.
- Apply potassium at 0.5–1.0 lb per 1,000 sq ft.
- Apply phosphorus only if your test shows low P.
- Water in with about ¼ inch.
- Sweep granules off sidewalks and drives.
- Keep fertilizer at least 10 feet from water.
- Skip nitrogen-heavy fertilizer after early September.
- Keep mowing and watering steady until dormancy.
Common Mistakes to Avoid
- Skipping the soil test, then applying unneeded phosphorus.
- Fertilizing before a heavy rain or on frozen ground.
- Using too much potassium.
- Leaving granules on driveways or sidewalks.
- Using high nitrogen too late in fall.
Costs and DIY vs. Pro Help
Here’s a rough idea of costs for common fall fertilizers. Prices vary by store and bag size.
ProductAnalysisApprox. Cost per 1,000 sq ftNotesMuriate of Potash0-0-60Low to ModerateStrong K source, easy to findSulfate of Potash0-0-50ModerateGentler, adds sulfurDiammonium Phosphate (DAP)18-46-0ModerateOnly use if test shows low PTriple Superphosphate0-46-0ModerateConcentrated P, no nitrogen
A lawn care professional can handle soil testing, rates, and timing for you, which may be worth it for large lawns or busy schedules.
Fast FAQs
Should I apply potassium if I fertilized in summer?
Yes. Light fall potassium helps with winter strength, especially if your soil is low.
Should I apply phosphorus every fall?
No. Only apply if your soil test shows low P or you’re planting new sod or seed.
Can I mix potassium with a fall pre-emergent?
Sometimes. Check both labels. If unsure, apply separately.
Is phosphorus safe near my pond or creek?
Keep it off hard surfaces and away from drains. Never apply before rain.
What if I’m overseeding with rye?
Apply needed phosphorus at seeding for better germination. Potassium is fine in light doses.
How can I check soil temperature?
Use a soil thermometer at 4 inches or check local OSU or weather sites.
What about iron or micronutrients in fall?
Focus on potassium first. Iron helps color, but it won’t replace potassium.
Putting It All Together
So, should you apply potassium and phosphorus to Bermuda grass in the fall in Oklahoma?
For most lawns, apply potassium to build winter strength and improve spring recovery.
Apply phosphorus only if your soil test says you need it or if you’re planting new sod or seed.
Time your application for soil temps of 60–70°F, use safe rates per 1,000 sq ft, water it in, and keep it off hard surfaces.
Take ten minutes this fall to get a soil test from OSU Extension or a local lab.
Then mark your calendar for mid-September.
Measure your lawn, grab your bag, and make one smart fall application.
Your Bermuda will thank you in spring with a thicker, greener lawn that stands out on the block.
