by Margaret Smith, PhD
Forage Agronomist

Late summer is a great time to establish new forage seedings—if you have adequate soil moisture AND some rainfall is predicted. Like the variation in temperature in Goldilock’s porridge, last year was TOO wet in many areas to establish forages in late summer, and, this year, parts of the Upper Midwest are far TOO dry. There is, though, much of our area where a seeding a new hayfield or pasture in the next month makes good sense.

Advantages and Disadvantages of Late-Summer Seedings

Advantages

  • Increase first-year yields (2021) compared to seeding next spring
  • Weeds controlled by preplant tillage and freezing temperatures in the fall
  • Soils at this time usually fit for preplant tillage, compared with frozen and wet soils in the spring
  • Frees time in the spring for other operations

Disadvantages

  • Requires a short-season crop that is harvested in mid to late summer to allow time for seeding
  • Potentially dry soils delay or prevent germination
  • Potentially hot temperatures may dessicate and kill seedlings
  • Herbicide residuals may damage new seedlings
  • Emergence date must be calculated back six to eight weeks before the fall killing frost, which varies from year to year

Soil Testing and Fertility

Late summer is an excellent time to pull and update soil tests, and going into a mid- to long-term seeding is the perfect time to correct fertility needs.

Liming and pH

  • Alfalfa: lime to pH 6.8
  • Red Clover, White Clover, and Birdsfoot Trefoil: lime to pH 6.5
  • Grass Hay or Pastures: lime to pH 6.0-6.5

Ideally, liming correction should be made at least 6 months before seeding. But if not done previously, now is the time before your current seeding! With your soil test results, follow your state guidelines for lime, phosphorus, potassium, and sulfur applications.

Check Herbicide History

Check the labels of the herbicide you applied this spring. Will crop rotation restrictions for those products allow planting a forage crop this fall? If not, wait and follow those label guidelines for planting dates.

Seeding Conditions

Ideal conditions in late summer for alfalfa and other forage seedings are:

  • Moist soils, but not wet
  • Moderate temperatures
  • Rainfall predicted within the 10 to 14 days following seeding

Seeding Date

Forage crops should be seeded and emerge in time to allow six to eight weeks for growth before a killing freeze—usually 26o F. Use the planting dates on the graphic below as a general guide. Seedling forages may overwinter when seeded later, but growers assume a higher level of risk with this strategy.

Late-Summer Seeding Date for Alfalfa, Other Perennial Legumes, and Perennial Grasses

 

From: Alfalfa Management Guide, American Society of Agronomy

Soil Preparation

Can no-till work for late summer seedings? No-till is a good way to conserve limited late-summer soil moisture and can work following a short-season crop, such as canning vegetables, field peas, a small grain, or a single-cut warm season grass, like German/foxtail or proso millet. The best scenario for no-till is where moisture is ample, and your alfalfa or forage seeding follows immediately after the previous crop harvest. When summer crops are harvested several weeks before a planned forage seeding, there is likely too much time for weed growth that will compete with new seedlings. If soil moisture levels are adequate and weed pressure is very light, either from competition from the preceding crop or from burndown with a herbicide, no-till is an option.

Take fertility needs into consideration, though. Phosphorus, potassium, and sulfur can be strip tilled into the field before seeding, but for best distribution, these macronutrients and lime are best broadcast and incorporated.

If weed pressure or fertilizer applications require tillage, till only as deeply as you need to incorporate lime and to fertilize or manure and to take out existing weeds. Firm the seedbed with a cultipacker or roller before seeding conventionally.

Seeding Depth

Seed ¼” to ½” deep for both forage legumes and grasses.

Weed Management

A great advantage of late-summer forage seedings is the relative ease of weed management. Neither herbicides nor companion-seeded small grains are needed for annual weed control. Fall freeze will eliminate any annual weed seedlings. An exception would be where perennial weeds are present. Late summer can be a good time to treat those with herbicide before seeding your forages.

Consider Alfalfa Autotoxicity

Alfalfa can be seeded into a thin, existing alfalfa stand in late summer, but only if that stand was seeded this spring. Alfalfa also can be interseeded into older grass-only hayfields or pastures. Don’t seed alfalfa into older, established alfalfa stands. Older alfalfa plants develop too high levels of their autotoxic compounds to allow good germination and root development of any new, nearby alfalfa seedlings. Wait at least 12 months following termination of established alfalfa before reseeding to alfalfa. Red clover, white clover, and forage grasses don’t exhibit similar autotoxic traits.


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