Planting new stands of alfalfa during the late summer is an excellent way to establish alfalfa. Late summer alfalfa seeding is not necessarily better than spring planting, but it does provide another option that may better fit your work schedule or rotational practices.

Small grains harvested in late July or early August provides a window for seeding alfalfa. However, this may have greater risk because soil moisture can sometimes limit rapid germination, and the ideal planting window is rapidly closing. Also of concern is the herbicides used for weed control. Be sure to check the label of any chemical applied this year to be sure there are not any replant restrictions that will inhibit alfalfa seedling establishment. The common herbicides Curtail, Harmony, and Starane, fit this restriction. BE SURE TO READ THE LABEL.

Late summer planting has many advantages over spring planting. Weed and insect pests are seldom an issue. Pre-plant incorporated herbicides or a companion crop is not necessary, nor recommended. Weeds that emerge are generally killed by the first hard freeze.

Soil temperatures are much higher in the late summer than they are in the early spring, so with adequate moisture, alfalfa seedlings will germinate, grow and develop a crop canopy at a much faster rate.

Fall seeded alfalfa generally has greater yield potential during the first full year of production. By seeding alfalfa during the late summer, forage producers can have the equivalent of an established stand the following spring. Additionally, springtime workload is reduced.

Late summer alfalfa establishment may offer the most advantage to producers with heavy, poorly drained soils. It is on these types of soils where seedling diseases such as Pythium, Phytophthora root rot, and Aphanomyces root rot often limit alfalfa establishment in the spring. Because the soil is both warmer and dryer during the late summer, these diseases are much less of a concern.

It’s not a perfect world, and thus there are risks in late summer planting. Generally, the biggest concern is the lack of moisture for germination and early seedling development. Timely seeding will reduce this risk significantly. So, if possible, time the rains and plant into moisture – or better yet, cut some hay, that usually invites rain! Another risk is the threat of an early killing frost and/or severe winter. Again, timely seeding is important to minimize these risks.

The general recommendation for summer planting in northern Minnesota is late July into early August. However, in most cases, the small grains are not harvested so the planting date may get extended. If you plant later, beware that there is a certain element of risk. Our fall weather has been much more favorable over the past several years, but that can change quickly.

As a rule of thumb, seed alfalfa 6-8 weeks before the average first killing frost. Seeding too late will not give the plants enough time to develop adequate root and top growth before winter.

Soil fertility and cultural requirements for late summer-seeded alfalfa are similar as with spring planting. Take a soil test and apply fertilizer or manure according to University recommendations. Be sure to firm the seed bed during or after planting. Not enough credit is given to the importance of firm seedbeds in successful alfalfa establishment; this is especially true for late summer planting. A loose, fluffy seedbed in August can severely reduce germination success. A firm seedbed improves seed-soil contact and maintains more favorable soil moisture conditions.

If you get an excellent catch, don’t be tempted to take a cutting late this fall. The root systems are not well developed and the risk of winterkill is increased significantly. Even with a large amount of top growth, alfalfa will not smother itself out during winter.

Jim Stordahl, Clearwater/Polk Counties
U of Minnesota Extension