Reseeding - why, when and how?

Published 16 August 13

Reseeding – Why, when and how!

Are your swards performing as you would like them to? Do you know which sward is the best-performing and which is the worst?  These are the starting points for deciding whether a reseed is the right option, according to DairyCo extension officer Piers Badnell.

Teagasc, in Ireland, looked at the grass production (t/DM/ha) at nine farms over two years, and highlighted the difference in the best and worst performing paddocks.

These figures show the range of performance across paddocks from one farm. It’s important to know which paddocks aren’t performing well on your farm and to do something about them.





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In some cases, better performing paddocks produced more than twice the amount of grass, under very similar conditions, compared with their worst performing counterparts.

To ensure pasture produces lots of high quality forage, and to ensure grass is genuinely the cheapest feed, it is vital to have a programme of regular reseeding. Old swards tend to perform mid-season when the going is easy but drastically underperform in the early spring and autumn. Young leys also respond better to nitrogen.

Reseeding  costs around £200per acre but on average you are likely to see 35% more grass yield in the first year, and 10% for the next four to five years.

But, before considering a full reseed or any improvement strategy for the pasture, it is essential to run a sward health check and to calculate the cost of reseeding carefully in relation to the likely profits.

Sward Health Check

  • The first consideration for the production of quality grass is ryegrass content. Does your sward contain less than the minimum target of 30% ryegrass? The goal is to have 70% ryegrass, so clearly levels below 50% need serious attention.
  • Next, sample the soil to check if the pH is at 6-6.5 or below and P and K indices are at 2. If they are not, plan to remedy this with a suitable lime-based product.
  • Check the soil profile for evidence of compaction, soil pans and heavy poaching. Subsoil any suspicious areas.
  • Inspect drains to ensure they are working properly, particularly in any damp areas.

Following the assessment and correction of these points there are two main choices when looking at a full reseeds, either conventional drilling or direct drilling.

Conventional Drilling

For the greatest conventional drilling value, spray with glyphosate to kill perennial weeds and, in particular, inferior weed grasses.

Allow five to seven days, or take agronomic advice, before cultivating for a complete kill. Then plough under any previous grass swards or arable residues, and follow this up with any required lime and fertiliser. 

Prepare a fine, firm 5-8 cm deep seedbed immediately prior to sowing and sow when soil conditions are neither too wet nor too dry, taking particular care with the timing of clover sowings.

Ensure that you calibrate the drill to the seed mixture you are using, as this varies from batch to batch and year to year. Cross-drilling, at half the seed rate in each direction, provides better cover; a similar technique can be used to improve calibration when broadcasting the seed. 

The optimum drill depth for grass seed is 1.5cm while clover mixtures are best sown with the coulters raised, so they just scratch the surface.  Consolidate the seedbed after sowing without compacting it, using a combination of flat and Cambridge rolls.


The aim of direct-drilling is to minimise the surface trash, to give new seedlings the best chance to establish and to remove the opportunity for other species to take up valuable water and nutrients from the surrounding soil environment. 

To reduce grass cover, mow the field just before drilling or graze very close to ground.

Spraying with glyphosate, as with the conventional drilling technique, as this lengthens the window for new seedlings to establish. 

If required apply lime after spraying, and remove any compaction layers by sub-soiling to a relevant depth just below the target layer. Any deeper is adding unnecessary cost to the operation for no long-term benefit.

Drill when the soil is dry so it will not smear, and use an appropriate drill – either a slot seeder, or for very well-grazed swards or open and worn-out ryegrass stubbles, a direct drill.  Again, cross-drilling at half seed rate in each direction will maximise evenness.  Rolling straight after drilling, at a slight angle to the slots, also ensures good soil contact. 

This method of establishment warrants a serious consideration of pest control, particularly slug pellets during moist conditions, and sprays to kill leatherjackets and frit fly. Agronomic advice here is valuable, as a background level of pests in a compacted, highly-tillered grass sward rarely shows damage, but the same field with young shoots and open soils means the odds are stacked against success.

Early Care

Whichever method of establishment is used, attention to early management of new leys is important to monitor how the crop is emerging and to know what its competition is.  

  • Weed seedlings should be checked within a month of emergence. Control at this stage will be much more effective than later on, given the greater susceptibility of weed seedlings to herbicides. 
  • Herbicides should always be selected and applied to tackle specific weed problems, with clover-safe sprays chosen for mixed swards. 
  • New leys generally compete well with pests, except when weather conditions limit their vigour, in which case control measures may be needed.