Improving existing leys through overseeding

Overseeding can be a cost-effective way to introduce clovers and herbs into an existing grass ley, boosting productivity, resilience and soil function without the disruption of a full reseed. Below, we explain how to prepare the sward, choose suitable species and select the right overseeding technique. 

Successful overseeding depends on reducing competition, maximising seed‑to‑soil contact and timing operations carefully. 

Overseeding is most successful when the existing sward is less competitive and soil conditions favour seedling survival. It is usually best done in early spring and late summer.

Strong spring grass growth can quickly outcompete seedlings, so careful preparation and grazing management are essential.

A dense, tightly bound sward limits light, space and moisture for new seedlings. Preparation aims to open the sward up before seed is applied.

Reduce sward height to 4–5 cm shortly before overseeding. This improves light penetration to the soil surface and reduces early competition.

Light trampling by stock (e.g. sheep) can improve seed‑to‑soil contact, but avoid doing this on wet ground that could become compacted.

Where swards are very competitive, use harrows or rakes to break up the surface thatch, expose soil and create gaps for seedlings.

Overseeding is more successful when around 40% of the soil surface is visible before seed is applied.

Not all species establish well into existing leys. Choose plants that are competitive enough to establish but compatible with the current sward.

Species well suited to overseeding include:

• White clover – persistent, spreads via stolons, well suited to grazing
• Red clover – high yielding and nitrogen fixing, but shorter lived
• Chicory – deep rooting, mineral rich and drought tolerant
• Ribwort plantain – supports trace element uptake and animal health
• Yarrow – competitive once established and tolerant of low inputs

Species choice should reflect soil type, drainage, grazing or cutting use, and the existing sward composition.

Broadcasting is simple and cost-effective, particularly for rejuvenating tired pastures, but seed-to-soil contact is critical:

• Graze or mow tightly before seeding
• Harrow aggressively before and after broadcasting
• Evenly distribute seed using a broadcast spreader
• Roll after overseeding to press seed into the soil

Success depends on:

• A fine, open sward structure
• Good soil moisture
• Minimal surface trash

Broadcast overseeding works best in early spring or late summer.

Drilling is generally the most reliable overseeding method, especially in dry or compacted soils.

Advantages include:

• Excellent seed‑to‑soil contact
• Reduced losses from birds and surface drying
• More consistent germination in dry conditions
• Minimal soil disturbance

Trials consistently show drilled overseeds achieve 15–25% higher germination than broadcasting, with particularly strong benefits during dry weather.

Seed rates should reflect the existing sward and the target species mix.

Typical overseeding rate for herbal leys: 5–8 kg/ha. Adjust rates depending on the density of the existing sward, the species being introduced and the desired proportion in the final sward.

Overseeding can increase competition and reduce seedling survival, while underseeding may fail to shift sward composition.