Overseeding GS4 / SAM3 Herbal Leys into existing grass

TF’s Regenerative Agronomist, Will Marris, looks at the key steps for establishing herbal leys into existing grass for the SAM3 and GS4 options…

It’s fair to say that Defra’s SAM 3 Herbal Leys option under the Sustainable Farming Incentive has been broadly welcomed by both farmers and advisors alike. Similarly, the GS4 Legume and Herb Rich Sward option has become increasingly popular under Countryside Stewardship Mid Tier and Higher Tier on whole or part parcels in rotation.

Multi-species herbal leys can help to improve soil health and structure and reduce fertiliser inputs (with the inclusion of nitrogen-fixing legumes). Herbal leys also offer greater farm resilience in the face of changing weather patterns, with improved drainage and resistance to drought conditions. From a livestock health perspective, herbal leys often have high protein and tannins. Their deep rooting structure offers a mineral-rich feed for livestock. That’s before we discuss the potential for carbon sequestration!

We strongly recommend that farmers fully embrace the wide-ranging benefits of utilising more diverse herbal leys within their farming system. Indeed, the vast majority of herbal leys we recommend to clients invariably contain a minimum of 4-5 species, depending on their farm location, soil type, and their objectives.

Key Advice on Overseeding Herbal Leys into Existing Grass

While herbal leys offer many benefits, they can be very tricky to establish and require careful management. Before you even think about drilling, it’s important to measure the status of your soils, plan your establishment strategy, and consider post-establishment grazing management to ensure success.

Have you tested your soil?

Testing your soil for basic nutrient status and addressing any nutrient imbalances or deficiencies is a vital first step. As a minimum, ensure there is sufficient nitrogen, potassium and phosphate, as well as key trace element levels, to aid good quality establishment of the herbal ley.

Have you spot-checked pH levels?

Although your pasture may look in good shape, the correct pH will give the herbs and legumes the best chance to establish and thrive.

Have you dug a hole?

Alongside nutrient testing, a visual check of the soil profile and sward is essential to identify potential compaction issues that will hinder establishment. Is there a mat of roots in the top few inches of the soil? If so, consider a sward slitter/grassland spiker to alleviate topsoil compaction and open up the root mat. If you can see deeper compaction, it’s probably worth considering a low-disturbance grassland subsoiler.

Root thatch and possible compaction at 2-3” depth. A grassland spiker will help to aerate and cut through thatch

Choosing the correct seed mix

Before you order seed, it’s worth assessing what is currently in your sward. Would some additional grass varieties help improve the sward? Is there any existing clover? How is it looking?

Most commonly available mixes will include red/white clovers and key herbs, such as plantain, yarrow, and chicory. But it is important to consider your needs. For example, chicory isn’t the best option if you want to silage the ley, while some plants might not suit your soil or farm environment. Get in touch if you need any advice.

Pre-Establishment

Before establishing the herbal ley, it is a good idea to get on top of any broad-leaved weeds, such are docks, thistles, and nettles, as no herbicides are allowed under CSS or SFI (unless to weed wipe, spot treat, or destroy a current ley to establish a new herbal ley).

Dead dock after herbicide application

Choosing the correct herbicide mix is important to control the weeds but not to leave any chemical residues that may compromise the herbal ley germination or early establishment. Please get in touch to discuss any potential issues.

Likewise, it is important to reduce the competition from the established grass before drilling. You can do this by grazing the sward hard to reduce biomass and allow sunlight into the base. Alternatively, you can tightly mow the grass or drill the herbal ley directly after cutting for silage.

Drilling the herbal ley

Control of drilling depth will be crucial, as the herbal ley seeds you will sow will be small. Generally, the shallower the better, so aim for a drilling depth of 10mm or less, with good seed-to-soil contact.

A disc drill is a good way to slot the seed into the grass sward with minimum disturbance. The key here is not to drill too deep. Set the disc to cut a slot for the seed no deeper than 10mm. Rolling after drilling is vital to ensure the slot created by the disc is closed effectively, giving good seed-to-soil contact and consolidation. A single pass with a flat roller is recommended; twice with a Cambridge roll to give the best results.

A SAM3 Herbal Ley overseed. Drilled with a Vaderstad Rapid disc drill. Legumes and herbs are establishing well after 3 weeks.

Broadcasting is a cost-effective method to overseed a herbal ley, and running over the field with a harrow before broadcasting will help to expose fresh soil for the new seeds. The harrow will also help remove dead thatch from the base of the sward, encouraging light and moisture into the base for the seeds. Rolling after broadcasting is even more important to ensure the seeds are pressed into the soil for good seed-to-soil contact. Again, a single pass with a flat roll or twice with Cambridge rolls is the bare minimum. If you plan to roll twice, ensure you roll once in the direction of broadcasting/wheeling and then a second time across the wheelings at a 45◦ angle to get the best consolidation.

Overseeding is best done when soils are warm and moist. However, try to avoid peak grass growth season to reduce competition. Base your drilling timing on soil moisture and temperature: you want soil temperatures of 10°C minimum to aid rapid establishment. Generally, April and August are ideal months for overseeding.

Once Established

Once the ley is well established, a light grazing regime will encourage the robust growth of the new plants. Aim to lightly graze the ley on a rotational grazing system around 6-8 weeks after drilling, depending on establishment and growth rate. (Seek advice if you are at all unsure.) However, it is essential to carefully manage grazing and avoid overgrazing during the first year of establishment. Livestock will naturally select the most palatable plants and graze certain species to extinction.

The best way to manage an overseeded herbal ley is to rotationally graze the ley, allowing ample rest periods to ensure good quality establishment and growth.

Advice and support

If you want any more information or assistance on introducing or establishing herbal leys (for SAM3 or otherwise) that are suitable for your farm and your objectives, please get in touch on 01347 844132 for a no-obligation chat or send us a message using our Contacts Page. We’re here to help.