Drought Risks To Late Summer Alfalfa Seedings

Oct 20, 2022

By Craig Sheaffer and Nathan Drewitz

Planting alfalfa alone or in a mixture with grasses in late summer is recommended because the potential for optimal air temperatures and soil moisture for establishment is good. In addition, there is much less competition with annual weeds compared to spring seedings; therefore’ herbicide use is seldom needed. Typical recommended seeding dates for central and southern Minnesota range from August 15th to September 1st.

Drought effects on seedling survival

CROP

Figure 1. An 8-week-old alfalfa seedling with four fully
developed trifoliolate leaves and a unifoliolate leaf. Seedling
is undergoing contractile growth leading to formation of a
submerged crown. It has a high probability of successfully
overwintering.

Drought during late August and September will delay germination until favorable soil moisture is available. To germinate, alfalfa seeds must absorb over 100% of their weight in water. Delayed emergence caused by dry soils increases the risk of establishment failure through winter injury because seedlings do not have time to adequately develop crowns and roots. Plants with a high probability of survival will have at least four trifoliolate leaves (Figure 1).
If adequate moisture is available, alfalfa seeds continue to germinate throughout the fall and even during winter. Alfalfa can germinate at temperatures as low as 32 F although it can take 2 weeks for germination. Unfortunately, seeds that germinate after mid-September have little chance of developing into plants that survive till spring. Growers can expect significant yield reductions from surviving plants.
What could change this prediction? An early and continuous snow cover of 6 inches or more that lasts until spring may result in greater seedling survival than expected. However, even then, seedlings with small root systems would have to withstand spring thawing and freezing cycles that can promote heaving of roots.

Time required for seedling growth

Seed germination and seedling emergence by early September at near optimum temperatures of 65-75 F will allow for 8 or more weeks of growth before a significant killing frost. In an earlier Crop News, we showed that alfalfa seedlings had good tolerance to air temperatures as low as 24F. For much of central and southern MN, these temperatures are not typically reached until early November.
With normal late summer temperatures, seedling emergence is complete within 2-7 days and the unifoliolate stage is reached in about 2 weeks. Contractile growth, which pulls the cotyledonary and unifoliolate nodes below the soil surface, and below ground crown formation begins as early as the unifoliolate leaf stage and continues until about 8-10 weeks after seedling emergence. This early growth protects the new crown and crown buds from low winter temperatures.

In addition to contractile growth, time is required for the development of 3-4 trifoliolate leaves, which generate carbohydrates that are stored in the roots. Simple sugars and starch are required for survival of the plants over winter.

Perennial grasses

Perennial grasses seeded alone or with alfalfa have an advantage in tolerating late emergence because they have hypogeal emergence. In hypogeal emergence, the seed and growing point stay below ground and are protected from winter injury by the soil. Perennial grasses, like orchardgrass, perennial ryegrass, and meadow fescue, still require the development of 3-4 leaves to reliably survive the winter.

Source : umn.edu

Video: Spring 2026 weather outlook for Wisconsin; What an early-arriving El Niño could mean

Northeast Wisconsin is a small corner of the world, but our weather is still affected by what happens across the globe.

That includes in the equatorial Pacific, where changes between El Niño and La Niña play a role in the weather here -- and boy, have there been some abrupt changes as of late.

El Niño and La Niña are the two phases of what is collectively known as the El Niño Southern Oscillation, or ENSO for short. These are the swings back and forth from unusually warm to unusually cold sea surface temperatures in the Pacific Ocean along the equator.

Since this past September, we have been in a weak La Niña, which means water temperatures near the Eastern Pacific equator have been cooler than usual. That's where we're at right now.

Even last fall, the long-term outlook suggested a return to neutral conditions by spring and potentially El Niño conditions by summer.

But there are some signs this may be happening faster than usual, which could accelerate the onset of El Niño.

Over the last few weeks, unusually strong bursts of westerly winds farther west in the Pacific -- where sea surface temperatures are warmer than average -- have been observed. There is a chance that this could accelerate the warming of those eastern Pacific waters and potentially push us into El Niño sooner than usual.

If we do enter El Nino by spring -- which we'll define as the period of March, April and May -- there are some long-term correlations with our weather here in Northeast Wisconsin.

Looking at a map of anomalously warm weather, most of the upper Great Lakes doesn't show a strong correlation, but in general, the northern tiers of the United States do tend to lean to that direction.

The stronger correlation is with precipitation. El Niño conditions in spring have historically come with a higher risk of very dry weather over that time frame, so this will definitely be a transition we'll have to watch closely as we move out of winter.