Grassland Reseeding Guide

Your field guide from sward assessment to establishment


Aim to renew 10 – 15% of your leys each year


  • Older leys (8 years +) will usually comprise 50% weed grasses or more
  • Aber High Sugar Grasses are typically 15 D-value units higher than weed grasses
  • Response to nitrogen is 5 times greater in modern ryegrasses than weed grasses

Full reseed or sward renovation?

Whilst short-term productivity can be improved cost effectively through a variety of over-seeding methods, there is no doubt that a full cultivation reseed is the best method of establishing a new ley.

Carry out a full reseed when any of the following are evident:

  • Production falls
  • Inadequate spring or autumn growth
  • Response to N declines
  • Regrowths take longer
  • Stock fail to clean up available grass
  • Sown species make up less than 50% of the sward
  • The cost of controlling weeds, pests and/or diseases is prohibitive
  • Poaching or compaction levels have become unmanageable
  • Rotational policy dictates a change of crop

Choose optimum timing

When to reseed?

England & Wales:

Spring or autumn reseeding can be equally effective, so do whatever best suits your farming system.

  • Sow no later than August when including red clover
  • Sow no later than mid-September when including white clover

Northern England & Scotland:

  • Spring reseeding allows time for swards to establish before winter
  • When summer/autumn reseeding and including red or white clover, sow no later than mid-August

Consider a brassica break crop

In the context of pasture renewal, a break crop offers the following advantages:

  • Disruption of grass-specific pest and disease cycles
  • Elimination of pasture-based animal parasites
  • Enhanced weed control opportunities
  • Extended opportunities to address soil nutrients and/or soil condition
  • Additional 4-8 t DM/ha production from the brassica

Identify priorities for reseeding

Your Pasture Health Check List:

  • Increased presence of docks, thistles, nettles, chickweed or other weeds
  • Unproductive grasses such as bents, meadow grasses, red fescue and Yorkshire fog
  • Drop offs in silage production or stock carrying capacity
  • Slow regrowths after cutting or grazing
  • Reduced response to fertiliser
  • Rejection or uneven grazing
  • Intermittent growth or shortening of growing season

If you have ticked any of the above, your ley is certainly beyond its productive life and in need of replacement.

Make a thorough sward assessment

Targets for sward assessment

  • 75% Ground cover
  • 30% Clover content (average over a season)
  • 50% Sward composition (PRG minimum)
  • 10% Broad leaf weeds (maximum)

Carry out the red stem test

As a general guide, perennial ryegrasses have a red colouration at the base of the stem and a shiny underside of the leaf - weed grasses do not – so carry out a simple field assessment to check your sward composition.

Assess your sward clover content

At the optimum sward content of 30% averaged across the season, white clover contributes 150kgN/ha





Test your soil pH

Optimum pH for plant growth and uptake of nutrients is 6 – 6.5.

Applying lime at 5 t/ha will raise pH by 0.4 units, but not for 9-12 months.

For a faster response apply a granulated lime product.

Test your P&K levels

Phosphate (P) and Potash (K) indices should ideally be at 2 for optimum sward performance, so apply fertiliser to the seedbed if necessary.

Low P = poor root development, poor use of nutrients

Low K = poor transport and utilisation of nutrients, poor growth

Assess the condition of your soils

Take a spade and dig out a sod to a depth of about 40cm.

Signs of water logging and compaction:

  • Rusty, grey, mottled colouration
  • Distinctive foul smell
  • Poor root penetration (should be 30cm and more)
  • Lack of earthworms (should be 10-15 in a spade-full)
  • No vertical cracks (5mm channels allow air, water and nutrients to circulate)

Rectify any soil structure problems

Match the solution to the problem:

Surface capping (0-10cm) - use a soil aerator with spikes or knives (e.g. below)

Compaction (10-15cm) - sub-soiler or sward lifter

Plough pans - sub-soiler or mole plough

Assess weed populations

Identify any major problems and control them in the old sward as this will make establishment of the new ley better and easier to manage.


Select grass mixtures containing varieties that are ranked on the Recommended Grass and Clover List.

  • Select top performing varieties; there is significant variation in performance even amongst RGCL listed varieties
  • Look for the ideal combination of yield (dry matter) and quality (D-value)
  • Consider other agronomic factors such as seasonal growth, ground cover and disease resistance
  • Ensure mixtures are fit for purpose, whether for cutting, grazing or dual purpose

Give your seed the best chance of germination:

  • Work the ground to a fine tilth
  • Sow when soil is moist and warm (minimum 5°C)
  • Use the correct seed rate (15kg/acre; 35kg/ha) to establish a dense sward
  • Optimum seed depth is 15mm (½ inch)
  • Roll before and after drilling for optimum consolidation - you should be able to walk on the field and leave no footmarks


Overseeding, or sward rejuvenation, can be a good way to improve the yield and quality of grassland whilst minimising any time out of production.

When should overseeding be used?

  • If leys still have a good proportion (50%) of perennial ryegrass present.
  • For a short-term boost in production.
  • Where land is steep or stony and difficult to reseed.
  • As a tactic alongside a full reseeding programme.

How to overseed effectively:

  • Ideally in the July – September period, following a tight grazing or silage cut.
  • Seed rate of 10kg/acre (two-thirds of a full reseed).
  • Ensure good soil-to-seed contact, through harrowing and rolling, as required. 

Return on investment

  • Estimated 10% increase in dry matter production
  • Increased D-value worth 0.5MJ/kg ME
  • Return on investment within the year of overseeding


Protect new leys by monitoring weeds, pests and diseases:

Newly sown pastures are more susceptible to weed ingress, pests and diseases than well-established grassland.

  • Identify weeds and control early by spraying or grazing
  • Monitor new leys for pest attack, with wireworm, frit fly, slugs, leatherjackets and chafers the most common threats

Graze to aid establishment:

Graze new leys lightly with sheep or young stock when grass reaches 7.5 – 10cm to consolidate roots and promote tillering.

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