When is it too Late to Plant Forages?

Stephen K. Barnhart, Estension Forage Agronomist, Iowa State University

Spring hay and pasture seedings are normally done from late February through late April in Iowa. The extended period of wet weather and possible flooding in 2010 may have many producers wondering whether they can get their forages planted this spring.

How late is too late to plant your Spring forage stands? The short answer is –into the first 10 days to 2 weeks into May. The ‘end of the spring forage planting season’ is generally limited by seedling development and growth into the summer months. Most forage seedlings are emerging and growing root systems into the top 1 to 3 inches of the seedbed during the 3 to 4 weeks following germination.

The increasingly dry and hot soil surfaces in late May and June increase the risk that the small forage seedlings do not establish. So, the risk depends on rainfall and soil temperatures from here on. If conditions turn normal or hotter and dryer than normal, the risk of late planted forage seeding failures increases. If late May and early June conditions remain cooler and wetter than normal, then later-than-desired spring forage seedings may survive very well.

If you do plant later than desired, be aware that you are still as vulnerable or more vulnerable to erosion and weed compe- tition. Keep cereal companion crop planting rates to half of a full seeding rate or less, and mow or clip new seedings sev- eral times during the early seedling development months to allow light to reach small developing legume and grass seed- lings. Also scout for and manage potato leafhoppers in new alfalfa seedings.

What about skipping spring planting and planting the new hay and pasture fields in late-summer? The success of ‘late summer plated forages’ is set by both the ‘planting window’ that provides for a 6 to 8 week establish- ment time requirement for seedlings before the first killing freeze of the fall, and the necessity of adequate existing soil moisture and likelihood of average or better fall rainfall.

For alfalfa and other forage legumes, the seed should be planted by Aug. 10 for the northern third of Iowa, by Aug 20 for the middle third of the state and by late August or the first week of September for the southern third of the state. Cool- season forage grasses can be planted a few weeks later in each of these zones.

The risk of stand failure is high if seed is planted in dry soil, and rainfall patterns for the remainder of the fall season are erratic.

Can purchased seed be carried over until fall or next Spring? Seed is perishable. Germination declines during storage and declines faster if seed storage conditions are warm and in high humidity. Certainly try to store carry-over seed in a cool, dry place. Even better, try to arrange for storage in a more desirable seed storage facility. If you do have concerns about the viability of carry-over forage seed, have a germination test done before planting, and adjust sowing rates to compensate for any germination percentage losses.