The best time to plant alfalfa in Oklahoma is between August 15 and September 15. This fall window gives seedlings enough warm soil and reliable moisture to establish strong roots before winter. Spring planting is possible but risky, and Oklahoma State University actively discourages it for most of the state.
The Fall Planting Window
August 15 through September 15 is the target for Oklahoma alfalfa growers. During this period, soil temperatures are warm enough for rapid germination (alfalfa germinates fastest at 77 to 86°F), and late-summer rains typically provide the moisture new seedlings need. Plants that get up and growing before the end of September have the best chance of developing deep enough roots to survive winter and produce strong yields the following spring.
If you miss that window, planting in October is possible but significantly riskier. Rainfall becomes less frequent, and seedlings may not reach adequate size before cold weather arrives. Without irrigation, an October planting is a gamble.
Spring Planting: When It Works
Spring-sown alfalfa in Oklahoma faces drying winds, heavier weed pressure, and more insect problems than fall plantings. If you do plant in spring, the window is March 15 to April 15, and success depends heavily on where you are. Eastern Oklahoma, where rainfall is more reliable, gives spring plantings the best shot. Elsewhere in the state, irrigation is essentially required to make a spring stand work.
If spring planting gets delayed past mid-April, stop. Plants won’t grow large enough before summer heat sets in. At that point, wait for the fall window instead.
Soil pH and Lime Timing
Alfalfa is pickier about soil pH than most forages. It needs a pH between 6.3 and 6.9 to thrive. Most Oklahoma grasses grow fine at 5.8 to 6.0, so a field that supported other crops may still be too acidic for alfalfa.
The catch is that agricultural lime takes months to change soil pH. You should sample and test your soil 6 to 12 months before your planned seeding date. If your pH is 6.5 or below, apply lime as early as possible and incorporate it into the top 6 inches of soil during seedbed preparation. Waiting until planting time to address pH problems is too late.
Preparing the Seedbed
Alfalfa seeds are small and need to be placed in the top 3/8 inch of soil. That only works on a seedbed that’s clod-free, level, and firm. “Firm” means more compacted than you might expect. Walk across your prepared field and look at your footprints: if you sink deeper than the sole of your boot, the soil is too loose. Another test is to try bouncing a basketball on the field. If it doesn’t bounce easily, the seedbed needs more packing before you plant.
On medium and fine-textured soils (clays and loams), plant seed 1/4 to 1/2 inch deep. On sandy soils, you can go up to 3/4 inch, though keeping it at 1/2 inch is a safer bet regardless of soil type. Seeds planted too deep may never emerge.
Seeding Rate and Inoculation
For a pure alfalfa stand, use 15 to 20 pounds of seed per acre. If your moisture, timing, and seedbed prep are all dialed in, you can drop to 10 to 12 pounds per acre.
Alfalfa relies on specialized soil bacteria to fix nitrogen from the air, and you can’t always count on those bacteria being present in your field. Inoculating seed at planting is standard practice. Many seed suppliers sell pre-inoculated alfalfa seed with a coating that extends the bacteria’s shelf life. Check the expiration date on the tag. If the seed has been stored for more than a year or exposed to high heat, re-inoculate before planting.
If you’re inoculating yourself, use a powdered peat-based inoculant with a sticking agent (commercial products work best, but a 1:9 mix of corn syrup and non-chlorinated water will do). Mix only enough seed for one day’s planting, keep the inoculant cool and out of sunlight, and re-inoculate any unused seed after 24 hours. Properly inoculated seed should flow freely through your planter without clumping.
Fertility Before Planting
Along with lime, incorporate phosphorus and potassium based on your soil test results. Phosphorus fertilizer is typically needed when soil test levels fall below 25 ppm, and potassium when levels are below 120 ppm. Even fields testing above those thresholds may benefit from additional fertilizer. A small dose of nitrogen at planting, around 15 to 20 pounds per acre, helps seedlings establish before the nitrogen-fixing bacteria on the roots are fully active.
Choosing the Right Variety
Alfalfa varieties are grouped by fall dormancy ratings, which indicate how quickly the plant goes dormant as days get shorter. For Oklahoma, varieties in the fall dormancy 4 through 6 range are appropriate. Lower dormancy numbers (more dormant varieties) are better suited to colder northern climates, while higher numbers stay productive longer into fall but are less winter-hardy. Within that 4 to 6 range, your choice depends on whether you prioritize extra fall growth or a wider safety margin against cold snaps.
Putting the Timeline Together
A successful fall planting starts well before August. Here’s what the calendar looks like:
- 6 to 12 months before planting: Test soil pH and apply lime if needed. This is the step most likely to derail a stand if skipped.
- Summer before planting: Apply phosphorus and potassium, prepare the seedbed, and firm it thoroughly.
- August 15 to September 15: Plant into a firm, clod-free seedbed at the correct depth and seeding rate.
- End of September: Seedlings should be visibly established. Stands not up and growing by this point face higher risk of winter loss.
For the small number of growers attempting spring planting in eastern Oklahoma or under irrigation, soil prep and liming should be done the previous fall, with seeding between March 15 and April 15.