Spring is here, despite this week’s chilly weather, and for many people, that means it’s time to plan for planting alfalfa.
Establishment is one of the key factors that can influence yield, quality and stand persistence for years to come, but our weather during planting windows has been less than favorable in recent years. This article will address some common questions about when to start planting in the spring.
Mature alfalfa plants and early seedlings are very cold-hardy. Newly germinated alfalfa plants can tolerate hard frosts without damage, but cold tolerance declines after the first trifoliate emerges. Since trifoliate leaves take around 15 to 25 days to emerge after planting, and it takes a while for our soils to dry out enough to be workable, we rarely see frost damage due to planting too early on tilled fields. In no-till systems during dry years, plan your planting date such that you’re planting within three weeks of the last expected hard frost. For a lot of our region, April 1 is frequently a good date to get started; waiting until April 10 to 15 may be more suitable if you live in far northeast Ohio or northern Pennsylvania.
Soil temperature
Soil temperature can play an important role in planning your optimal planting date. While modern alfalfa varieties can germinate down to around 32 F, it will take over two weeks to reach 50% germination when the soil temperature is in the 30s. In soils above 40 F, alfalfa reaches 50% germination in about three days. This means that soil temperature can swing the date to first trifoliate leaf by about five to 10 calendar days. Earlier April plantings with higher soil temperatures can be riskier if we get hard frost later in the month, since alfalfa becomes less cold-tolerant after trifoliates emerge.
Weed pressure. Planting date can also impact weed pressure. The critical period for weed control ends at or before the 7th trifoliate growth stage, and it will usually take earlier plantings on cooler soils a bit longer to reach this stage.
Many of the herbicides available for post-application in new alfalfa seedlings are also in group 2 herbicides (ALS-Inhibitors), which are less effective in cold weather. If you expect to plant in cold weather, including a companion crop like oats or barley is a great way to provide ground cover and reduce weed pressure; annual grass companion crops have the added benefit of increasing protection against late-season frosts, too.
The annual grass crop should then be harvested as silage or baleage in the boot stage to increase first-year yields and allow maximum alfalfa growth if the summer becomes dry.
Getting ahead
Spring is also a great time of year to think about where you might be planting alfalfa in 2027 so that you can get ahead of any perennial weeds. Quackgrass, sedges and thistles can be tough to control in alfalfa, so it’s helpful to get ahead of them during the preceding crop using a mix of mechanical control and well-timed herbicides.
Inoculant and starter fertilizer decisions will depend on your soil type and crop rotation. Inoculating seed may not be necessary if you’ve grown alfalfa or sweet clover in that field in the last three years, but it’s inexpensive and can prevent nodulation failures.
Since inoculants contain living bacteria, it’s important to follow the manufacturer’s instructions for storage and application methods so that the bacteria are lively and able to colonize the alfalfa roots. Be sure to read your seed tag before adding additional inoculants, as coated alfalfa often contains inoculants and fungicides along with lime or clay.
Inoculants can also be sensitive to fertilizers and many pesticides, so if you use an inoculant or coated seed, any other at-plant products should be applied separately. Nitrogen starter fertilizer is not usually needed for legumes, but low rates of N can provide some benefit on cool soils. Limit any N applications to 10 pounds/acre at most to improve return-on-investment and reduce the risk of delayed nodulation.
While we all hope for a smooth planting season with good weather, it’s also helpful to have a backup plan. If you get rained out of the spring planting window, consider options for planting high-biomass summer annuals; these crops can help provide needed forages this growing season, and can prevent weed issues from getting worse while you wait for the next opportunity to plant perennials.
