How to ensure success with overseeding this autumn
After the exceptionally dry summer, most livestock farmers will seek to improve swards that have suffered from drought
Overseeding into an existing sward can be a low-cost alternative to ploughed reseeding, but without careful planning, it can easily fail.
The best months to attempt an overseed or reseed are usually April and August when there is adequate soil moisture or a forecast for rain. However, depending on location, many may have to wait for the right conditions until late September, even early October. Much depends upon a month of good weather after drilling, but the chance of failure, particularly for legume and herb species, increases as daylength shortens and air and soil temperatures drop.
Preparation and attention to detail are always crucial when it comes to establishing or improving a sward – this year, it will be even more so.
Overseeding versus reseeding
When a sward becomes dominated by broadleaved weeds, unproductive grass species, or is poached, reseeding following ploughing is an option, though it shouldn’t be the default choice. Reseeding does mean restricting field use until the soil naturally develops a structure that can bear the weight of livestock and machinery again.
Overseeding, on the other hand, can revitalise a worn sward, usually with less expense and downtime. Unlike reseeding, soil structure and organic matter remain intact. Future drought resilience can be improved by adding deeper rooting species to the seed mixture.
Success isn’t guaranteed with either reseeding or overseeding – with the right preparation and techniques, an overseed should take well in most situations.
Tim’s top tips for a successful overseed
Do the groundwork
Poor soil fertility is a common cause of seeds failing to establish. Before attempting an overseed, analyse the soil to assess whether the pH, phosphorus (P), potassium (K), and magnesium (Mg) levels are close to target. A small amount of P fertiliser at drilling will aid seedling rooting and establishment, as can a biostimulant seed dressing.
Dry weather will have naturally remediated soil compaction somewhat by shrinkage and fissuring but it won’t be 100%. To avoid an uneven, lumpy, surface which a drill may struggle with, deal with soil compaction immediately post-drilling to ensure rooting can reach maximum depth.
Suppress competition
Minimising competition from the existing sward is a must. Weeds should be dealt with using cultural or herbicide control. Glyphosate use is possible but care is required to avoid toxins and acids from dead herbage. Always follow label instructions.
As well as minimising competition, seeds need soil contact and light to grow, so spray, graze, or cut the existing sward tightly. If the sward is matted, harrow to break-up and remove thatch to expose soil.
Do not apply nitrogen (N) for an autumn reseed as N will be mineralised from the soil as it wets again. If overseeding in the spring, withhold N until seedlings are able to compete with the existing sward.
Choose the correct drill
It’s tempting to use whatever drill is most convenient, but the wrong drill for your soil type could compromise establishment. Drill choice will depend upon soil type, stone content, soil moisture and ensuring good seed-to-soil contact.
Keep drilling shallow – particularly for species with small seeds such as clover – and drill at a speed which ensures that seed is placed in a tilth, not dropped onto the soil surface.
For heavy, clay soils, disc or tine drills may suit – the key point is to create a tilth. If the ground is too wet, it’s best to wait, time allowing. Discs may struggle for purchase with light, sandy soil so carefully controlled tines may be the better choice.
Discs will ride over stones, but may bounce if drilling too fast. The heavier a tine, the more it is likely to pull up stones.
Drills generally have some form of following roller, for depth control. For drills without a roller, rolling immediately post-drilling will help with seed-to-soil contact – less so conserving moisture as the soil is largely undisturbed. Take care that rolling will not close slots tightly, thereby preventing emergence.
Prepare for invasion
Seedlings are a pest’s favourite food so take precautions. Consider adding slug pellets to the seed in the drill, particularly a slot drill, or apply separately soon after.
Frit fly can be troublesome – they tend to emerge late August through to late September. Drill as late into autumn as possible, daylength and temperatures allowing. If it’s a likely problem, keep an eye on monitoring forecasts.
Wireworm and leatherjackets are difficult to control, other than to try flat-rolling or hope for the local rook population to pitch up.
Aftercare
If conditions allow, lightly graze up to 10-days post-drilling to suppress the existing sward. Continue to reduce competition by controlling weeds with selective herbicides or grazing. Resume light grazing when the seedlings are well rooted. Tug test seedlings with finger and thumb and if the root cannot be easily pulled out, it’s safe to graze.