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Late Summer Pasture Seeding
by Jacob Hawes, NRCS Area Grazing Specialist
The late summer seeding window begins in August for pasture and hay plantings, and although it is not as popular as the spring seeding option, it can still be a great opportunity to get cool season pastures established this year. There are several advantages to seeding late summer versus the spring, that may ease some apprehensions about seeding during this timeframe.

By the time we reach August 1, cool season pastures have already produced most of their biomass for the season and the remaining production has slowed down significantly. By renovating pastures at this time of year, the producer doesn’t lose the most productive part of season waiting for their new seeding to establish. Likewise on cropland, if the producer is looking to convert ground to pasture, it allows production out of those acres earlier in the year, either by planting a small grain to harvest or planting annual forages to supplement their livestock’s daily needs prior to establishing new pastures. By next June, newly seeded pastures should be established well enough to hay or graze and still have good biomass production.

Weed emergence also decreases as we get closer to fall, which is another advantage to late summer seeding. According to Werle, Rodrigo, et al. in “Predicting Emergence of 23 Summer Annual Weed Species” common weeds like ragweed, velvet leaf and lambsquarter will typically have received the necessary growing degree days to reach 90% seedling emergence by July and pigweed and waterhemp should reach the same level of emergence by August. This gives producers an opportunity to seed new pastures without excessive weeds competing with new seedlings, assuming adequate measures to control existing weeds prior to seeding are implemented. If residual herbicides are used, ensure adequate time has passed before seeding to ensure that there will not be any affects to new seedings.

Regardless of the time of year, seed bed and site preparation are critical to allow new seedlings to establish well. The existing cover should be killed or suppressed prior to planting to reduce competition to new seedlings as they establish. Prior to seeding, collect soil samples and amend soils according to fertility and lime requirements specified in Iowa State University’s PM 869 “Fertilizing Pasture” and PM1688 “A General Guide for Crop Nutrient and Limestone Recommendations in Iowa”. If ag lime is needed, it is best if it is incorporated 6-12 months prior to seeding to allow time for the soil pH to adjust. If required, N, P, and K can be applied prior to or at seeding. Seeding can be done using a conventional grain drill on tilled soils, but a no-till drill is critical if seeding into sod to ensure that seeds are placed at a proper seeding depth and adequate seed to soil contact is achieved. Seedings should be done 6-8 weeks prior to the first killing frost and shouldn’t be hayed or grazed that fall to reduce the risk of winterkill. Our earlier frosts suggest completing the seeding by August 20 for successful seeding

The major drawback to seeding in late summer is often the lack of adequate soil moisture and precipitation to get seeds germinated and growing. Currently, most of the northeast area has received adequate precipitation, but a few counties in the area are experiencing abnormally dry and moderate drought conditions. Seeding during these conditions may end up failing and force a replant in the spring. If conditions are dry in your area and adequate soil moisture is not available, plan to defer seeding until next spring when precipitation and moisture are more consistent.