Knowing when to plant alfalfa in the fall is the single most important factor for a successful stand. Get the timing right, and you give your crop the best chance to establish strong roots before winter, leading to a productive field for years to come.
This guide walks you through the optimal autumn planting timing for your specific area. We’ll cover the science behind the schedule, the steps to take, and how to avoid common mistakes.
When To Plant Alfalfa In The Fall
Planting in the fall is all about balancing time and temperature. Your young alfalfa seedlings need enough warm days to grow, but not so many that they put on excessive top growth. The goal is to focus their energy on developing a robust root system.
Understanding the “6-Week Rule”
The most reliable guideline is to aim for a planting date that gives seedlings at least 6 weeks of growth before the first killing frost. A killing frost is typically defined as a hard freeze at or below 25°F (-4°C) that halts plant growth.
During these crucial weeks, the plant will establish a strong taproot and develop several sets of leaves. This stored energy is what carries it through the dormant winter months.
How to Find Your Target Planting Window
Your local average first frost date is the key. You can find this through your local cooperative extension service or trusted weather sites.
- First, look up the average first killing frost date for your town or county.
- Next, count backwards 6 to 8 weeks from that date. This period is your ideal fall planting window.
- For example, if your average first frost is October 20th, your target planting window would be between late August and early September.
Regional Timing Examples
These are general examples; always confirm with local resources.
- Upper Midwest & Northern States: Late July to mid-August.
- Mid-Atlantic & Central States: Mid-August to early September.
- Southern States & Lower Elevations: Early September to mid-October.
- Western States (intermountain): Early August to early September.
Why Timing is So Critical
Planting too early or too late in the fall leads to distinct problems.
Risks of Planting Too Early
- Excessive Growth: Plants may grow too tall and lush, wasting energy on leaves that can be damaged by frost.
- Disease and Pest Pressure: Warmer soils and longer exposure can increase issues with weeds, insects, and fungal diseases.
- Winterkill Risk: Tender, overgrown plants are more susceptible to winter injury.
Risks of Planting Too Late
- Insufficient Root Development: Plants won’t have time to store enough carbohydrates in their roots.
- Seedling Weakness: Tiny seedlings are easily heaved from the soil by freeze-thaw cycles.
- Complete Failure: A very late planting may not germinate at all before cold weather arrives.
- Lime if needed to raise the pH. This takes time, so plan ahead.
- Ensure good phosphorus and potassium levels based on your soil test report.
- Prepare a firm, weed-free seedbed. A loose, fluffy bed will dry out quickly and hinder establishment.
- Drill Seeding: The preferred method. Set the drill to plant seeds no deeper than 1/4 to 1/2 inch in fine-textured soils, and no more than 3/4 inch in sandy soils.
- Broadcast Seeding: If broadcasting, follow by a light harrowing to cover the seed and ensure good soil contact. Rolling the field after seeding is highly recommended to press seed into the soil.
- If rainfall is lacking, a light irrigation can be beneficial to get seeds started.
- Control weeds. Fall-emerging winter annual weeds can outcompete young seedlings. Scout your field regularly.
- Avoid any grazing or cutting in the fall. Let the plants focus all energy on root development.
- Poor Germination: Often caused by planting too deep, soil crusting, or insufficient soil moisture at seeding.
- Weak, Thin Stands: Can result from late planting, low seeding rates, or competition from weeds.
- Winter Heaving: Where plants are pushed out of the soil. This is most common in poorly drained, heavy clay soils and with late-planted seedlings that lack deep roots.
Soil Temperature: Your Secret Planting Signal
While the calendar is a great guide, soil temperature is your on-the-ground confirmation. The ideal soil temperature for alfalfa germination is between 65°F and 85°F (18°C-29°C).
Use a simple soil thermometer at a 2-inch depth in the morning. If your soil is within this range and you’re within your calculated planting window, conditions are perfect. Planting when soils are below 50°F (10°C) significantly delays germination and increases risk.
Step-by-Step Fall Planting Guide
Follow these steps to ensure your fall planting is succesful.
1. Field Selection and Preparation
Alfalfa requires well-drained soil to thrive. Test your soil pH and fertility 3-6 months ahead of time. Alfalfa needs a pH of 6.5 to 7.0 for optimal growth.
2. Seed Selection and Inoculation
Choose a winter-hardy variety rated for your region. Always use fresh, high-quality seed. This is not an area to cut corners.
Alfalfa requires specific rhizobia bacteria to fix nitrogen. Even if the seed is pre-inoculated, use a fresh peat-based inoculant labeled for alfalfa at planting. This step is cheap insurance for a strong start.
3. Seeding Method and Depth
Proper seeding depth is non-negotiable. Alfalfa seeds are small and must be planted shallowly.
Seeding to deep is a common cause of failure. If in doubt, err on the shallow side.
4. Post-Planting Management
Your job isn’t done once the seed is in the ground. Good moisture is critical for germination.
FAQs on Fall Alfalfa Planting
Can I plant alfalfa in October?
It depends entirely on your location. In the Deep South, October may be fine. In the North, it is almost always to late. Always use the 6-week pre-frost rule as your primary guide.
What is the latest date to plant alfalfa in autumn?
The absolute latest date is 6 weeks before your average killing frost. Pushing past this date greatly increases the risk of winterkill and stand loss.
Is it better to plant alfalfa in spring or fall?
Both have advantages. Fall planting often results in less weed competition and can yeild a full first harvest earlier the next summer. Spring planting avoids winter risks but battles more weeds. In many regions, fall is preferred for its establishment benefits.
How do I protect my fall-planted alfalfa over winter?
The best protection is correct timing and good soil fertility. A well-established plant with a strong taproot is its own best defense. Some growers leave a light stubble (4-6 inches) to help trap insulating snow, but the main key is ensuring the plant is properly dormant before severe cold.
Troubleshooting Common Fall Planting Issues
Even with good planning, challenges can arise. Here’s what to look for.
If your fall stand looks thin by late October, consult an agronomist. Overseeding in the fall is rarely effective; it may be better to assess in spring and consider reseeding if necessary.
Mastering when to plant alfalfa in the fall sets the stage for everything that follows. By aligning your work with nature’s schedule—giving your crop those vital weeks of growth before winter—you invest in the future productivity of your field. Take the time to find your local frost date, prepare your seedbed well, and watch the weather. With careful attention to timing, you’ll be rewarded with a dense, healthy alfalfa stand ready to thrive come spring.