During a recent field visit, I met with a grower concerned about the declining productivity of their alfalfa stand and the feasibility of overseeding as a solution. This challenge prompted an important discussion around options, best practices, and critical considerations for improving older alfalfa fields. 

When should overseeding be considered?

Overseeding becomes a practical strategy when alfalfa plant populations fall below five plants per square foot. At this threshold, stands typically experience significant yield reductions, making continued production without intervention economically unsustainable. Fields reaching this decline, especially after three to four production years, may benefit from introducing compatible forage species to extend stand life and boost yields. Overseeding offers an opportunity to extend stand life by one to several seasons, improve forage yield, suppress weeds, and better match hay products to different livestock markets. However, overseeding healthy, weed-free, and dense alfalfa stands is discouraged because it can unnecessarily complicate marketing and reduce forage quality. Also, if your older alfalfa stand is heavily infested with weeds like dandelion or quackgrass, it’s probably better to rotate the field to another crop instead of trying to extend its life by overseeding. Overseeding won’t solve serious weed problems and may not give you the return you’re looking for.

Overseeding options 

In selecting the right overseeding strategy, carefully align your choice of forage species with your production goals, soil, and climatic conditions. For fields intended to remain productive for less than a year, overseeding with annuals is recommended. Conversely, if you are seeking to maintain production for two to three more years, perennial options are preferable. The market should also guide your decision, for example, horse hay markets prefer grass-alfalfa mixtures, while the dairy industry demands high-protein forage such as pure alfalfa or clover-alfalfa mixes. Overseeding options broadly fall into two categories: annuals and perennials.

Annual overseeding options

Among the annual overseeding options, cereals like oats, barley, wheat, and triticale have been extensively tried and are recommended for their ability to boost early-season yields significantly. Seeding rates for cereals range between 40 and 60 pounds per acre, depending on the planting date and the existing alfalfa population, with higher rates advised for late plantings or severely thinned stands. These cereals contribute heavily to the first harvest, sometimes increasing yields by one to three tons per acre over alfalfa alone. However, you should be prepared for a longer curing period, as the increased biomass and moisture content complicate haymaking, especially in early spring. 

Annual ryegrass, particularly tetraploid varieties, should be seeded at rates between four and eight pounds per acre. It is notably more tolerant of saturated soils than cereals and typically cures faster after cutting. Early greenchop harvests are common, with later harvests suitable for hay when weather allows. However, you must monitor nitrogen levels closely, as excess nitrogen combined with lush ryegrass growth can increase the risk of nitrate accumulation in forage.

If your target is dairy or horse hay markets with higher protein needs, overseeding legumes into alfalfa stands offers a more suitable path. Berseem clover is the most recommended annual legume for overseeding. Closely resembling alfalfa in appearance and nutritional quality, berseem clover enhances yields by up to two tons per acre during the first three to four harvests after overseeding. It is especially valuable in poorly drained fields where alfalfa struggles, as it tolerates temporary water saturation and resists damage from weevils. Berseem clover should be seeded at rates of six to twelve pounds per acre. However, recognize the challenge of drying berseem forage in early spring, where moist conditions delay curing and elevate the risk of mold. Alternatively, the availability of silage or greenchop markets can mitigate this issue. Remember to choose varieties with strong disease resistance to help maintain stand vigor. 

In situations where overseeding must take place later in the spring, sudangrass may present a viable warm-season option. It is typically seeded after the first, second, or even third alfalfa cutting, using rates between 40 and 60 pounds per acre. These seeding rates are good for regulating over-tillering and ensuring fine stem growth. Sudangrass is especially useful in salvage scenarios where cool-season options are no longer feasible. Though it is more commonly suited for greenchop or silage, the sudangrass-alfalfa mixture can be managed for quality hay by harvesting when plants reach 24 to 30 inches in height. However, you need to test nitrate accumulation and prussic acid toxicity, especially in fields subjected to drought stress, excessive nitrogen, or frost. In the right conditions, overseeded sudangrass can produce two to three additional summer harvests and extend the economic life of an otherwise declining alfalfa field.

Perennial overseeding options

Perennial overseeding options offer a longer-term solution for those planning multi-year stand extensions. Orchardgrass, tall fescue, perennial ryegrass, and bromegrass have each been evaluated for compatibility with alfalfa systems. Orchardgrass is particularly favored for high-elevation or cooler regions and fetches premium prices in the horse hay market. Perennial ryegrass and kemal festulolium, a ryegrass-fescue hybrid, offer robust spring yields but may outcompete alfalfa during summer cuttings if not carefully managed. Tall fescue provides rapid establishment and high yields, but its aggressive growth can crowd out alfalfa within two years, making it better suited for short-term mixtures. Bromegrass is less competitive, but its establishment is slower and yields are lower compared to other perennials. These options should be planted using seeding rates from four to eight pounds per acre for orchardgrass and ryegrasses, and 20 to 30 pounds per acre for bromegrass. If you choose to plant fescue, make sure to select endophyte-free varieties, as endophyte-infected fescues can negatively impact livestock health.

Red clover stands out among perennial legumes for its value in alfalfa overseeding systems. It tolerates poorly drained soils, competes effectively against weeds, and maintains forage quality comparable to alfalfa, with slight yield peaks during the cooler spring and fall periods. It can potentially increase yield by up to two tons per acre in poor-condition alfalfa stands. Red clover should be seeded at eight to twelve pounds per acre, and patience is needed, as significant yield contributions often do not materialize until the second growing season after establishment. One thing to watch out for with red clover is its higher moisture content—it takes longer to cure than alfalfa, so you’ll need to allow extra drying time to avoid quality losses or mold issues.

Stand establishment and harvest management

Two different establishment research studies offer related suggestions on planting dates, one states that in the Intermountain Region, planting of annual grasses generally occurs from February through April, whereas perennial grasses are established either in the late summer months of August and September or during the early spring window from March to April. Another study recommends overseeding cool-season grasses, legumes, and cereals in April, once the soil has dried enough for planting. While warm-season annuals such as sudangrass thrive under high temperatures and establish rapidly once soil temperatures exceed 60°F.

If you're planning to add legumes to a thin alfalfa stand, you should inoculate the seed before planting to promote good nodulation and effective nitrogen fixation. For grasses and cereals overseeded into alfalfa, be sure to apply between 40 and 60 pounds of nitrogen per acre with each cutting applied when grasses are four to six inches tall. However, if you applied manure during the previous fall or winter, you may already have enough nitrogen in the soil and might not need to add more.

Proper establishment practices are critical to the success of any overseeding endeavor. Minimal soil disturbance is ideal to preserve existing alfalfa crowns. Therefore, techniques such as light disking, spring-tooth harrowing, or no-till seeding are recommended. Rolling the field post-seeding enhances soil-seed contact, promoting more uniform germination. If conditions are dry, light irrigation following seeding is advantageous to ensure prompt establishment before winter dormancy sets in.

When managing mixed stands, you'll need to adjust your harvest timing. For grasses, plan to cut early—ideally at the vegetative to early boot stage to preserve quality and give your alfalfa a better chance to regrow. If you're growing legumes like berseem clover, make sure to harvest before full bloom to maintain high quality and avoid issues with mold. Also, keep in mind that spring growth can get heavy, so you'll want to use mowers and rakes that can handle large volumes of forage. Forming your swaths properly is also important to help the crop dry down efficiently.

Forage quality expectations from overseeding

Table 1. Range of typical crude protein (CP), acid detergent fiber (ADF), and neutral detergent fiber (NDF) levels of alfalfa and overseeded species, Long et al. (2003).

Notes:

• Vegetative – Leafy growth; few stems; no reproductive growth
• Early bud – Initial buds visible at a few stem nodes
• Early bloom – 25% of plants have emerged seed heads; pollen just beginning to shed
• Early heading – The seed head first starts to emerge from the uppermost leaf sheath on the grass stem.

References

1. Canevari, M., Putnam, D., Lanini, W., Orloff, S., Reed, B., Vargas, R.  (2000). Overseeding and companion cropping in alfalfa. University of California Agriculture and Natural Resources Publications. 
2. Gildersleeve, R., Undersander, D., & Wood, T. (2003). Seeding into an existing alfalfa stand. In focus on forage (Vols. 5–5, Issue 9, pp. 1–2). University of Wisconsin–Extension.
3. Long, R., Putnam, D., & Canevari, M. (2003). Overseeding and management of older alfalfa stands. In Proceedings, California Alfalfa and Forage Symposium. University of California Cooperative Extension, University of California, Davis 95616.