Korean Lespedeza (Lespedeza stipulacea) is an annual, warm-season legume valued across the mid-South and Midwest United States for its utility as a forage crop, hay source, and soil improvement tool. This plant provides high-quality summer grazing when cool-season grasses are often dormant, offering a significant advantage for livestock operations. As a legume, it naturally fixes atmospheric nitrogen, enriching soil fertility and making it an effective cover crop for erosion control. Successful establishment relies heavily on selecting the correct planting time and ensuring the seed is placed properly.
Optimal Planting Timing
The timing for planting Korean Lespedeza involves choosing between two distinct windows: dormant seeding in late winter or conventional seeding in the spring. Dormant seeding, often called frost seeding, occurs when the ground is frozen or before the final hard freeze, typically from early February through early March. This method relies on the natural freeze-thaw cycles of the soil to mechanically work the small seed into the surface layer.
This approach eliminates the need for mechanical seedbed preparation and is particularly effective when overseeding into established pastures or grain stubble. The drawback of dormant seeding is that germination is less reliable, as success depends entirely on sufficient moisture and temperature fluctuations in the late winter environment.
Conventional spring planting is generally more dependable and should be scheduled after the danger of a hard frost has passed. As a warm-season legume, Korean Lespedeza requires warmer soil temperatures for successful germination and emergence. Planting should be delayed until the soil temperature is consistently above \(60^{\circ}\) Fahrenheit, with an ideal minimum of \(65^{\circ}\) Fahrenheit, which often occurs from mid-March through early May depending on your latitude. Planting during this window ensures rapid germination and growth, allowing the plant to better compete with weeds. Planting too early risks poor germination, while planting too late can expose young seedlings to intense summer heat and drought stress.
Essential Site and Soil Preparation
Preparing the site properly is important for successful lespedeza establishment, even though the plant is known for its tolerance of poor soils. While Korean Lespedeza can grow in acidic soil with a pH as low as 5.0, optimal growth and highest yields occur when the soil pH is maintained between 6.0 and 6.5. A soil test should be conducted several months before planting to determine the pH level and nutrient requirements.
If the soil pH is below the desired range, agricultural lime should be applied and incorporated well in advance of seeding, ideally three to six months prior. This time lag allows the lime to neutralize soil acidity, making nutrients more available to the young seedlings. Although the plant tolerates low fertility, it responds well to phosphorus and potassium fertilization, which should be addressed based on soil test recommendations.
A firm, finely tilled, and well-settled seedbed is necessary for the shallow planting depth required by this small-seeded legume. Land should be lightly disked or harrowed to break up large clods and then firmed with a cultipacker or roller before the seed is applied. A firm seedbed prevents the seed from being buried too deeply, which is a common cause of stand failure. Aggressive perennial weeds should be controlled prior to planting, as young lespedeza seedlings are poor competitors against established weeds.
Planting Techniques and Depth
The small size of the Korean Lespedeza seed makes planting depth the single most important technical factor influencing establishment success. The seed should be placed very shallowly, ideally between \(1/4\) to \(1/2\) inch deep, and should never exceed \(1/2\) inch. Deeper planting quickly exhausts the small seed’s energy reserves before the seedling can push through the soil surface.
Two primary techniques are used for planting the seed: broadcasting and drilling. When broadcasting the seed over a prepared seedbed, a higher seeding rate is necessary to compensate for uneven distribution and reduced seed-to-soil contact. Broadcasting rates typically range from 25 to 40 pounds of pure live seed per acre. After broadcasting, the area must be immediately rolled with a cultipacker or lightly dragged to press the seed into the soil surface and ensure good contact.
Drilling involves using a specialized seed drill or a grain drill with a small seed attachment, which allows for more precise depth control and a lower seeding rate. When drilling, rates can be reduced to 15 to 25 pounds per acre for a pure stand. The drill must be calibrated carefully to place the seed at the \(1/4\) to \(1/2\) inch depth, as setting the drill too deep will significantly reduce emergence. Regardless of the method chosen, inoculation of the seed with the correct species of Rhizobium bacteria immediately before planting is necessary to facilitate effective nitrogen fixation.