CSAM3Herbal leys

What it actually is

A ley with more in it than grass. GOV.UK's stated aim is that there is an established herbal ley with a mixture of grasses, legumes and herbs or wildflowers to provide varied root structures, and areas of flowering plants from late spring and during the summer months. The page says the action is designed to produce a high volume of forage with minimal use of inorganic fertiliser, to improve resilience to drought, and to help improve and maintain the soil's structure, carbon, biology and fertility.

Grazing and cutting are both permitted on the established ley.

Source: GOV.UK, CSAM3 action page, checked 02/08/2026.

What it pays, and what that comes to

The rate is in the panel at the top of this page. Multiplied out:

Source: arithmetic on the payment rate shown at the top of this page, which comes from Tilth's copy of the GOV.UK action catalogue and carries its own last-checked date. The 20 hectares is an illustration.

Is it worth it on your ground?

Step one: what the seed costs, and how many times you buy it. As with the legume fallow, the timing requirements put two sowings inside the three years. You establish by early autumn within 12 months of the start date, maintain the ley in the same place for a period of time that can reasonably be expected to achieve the action's aim, which GOV.UK says will usually be the end of the second summer after sowing, and then re-establish by early autumn, at the same place or a different one.

Source: Boston Seeds' own listed price and stated sowing rate for the CSS2 Herbal Ley SAM3 mix, looked up 23/08/2026. The site displays prices with an inclusive and exclusive of VAT toggle and £115.00 was read in the inclusive state. The timing that produces two sowings is from the GOV.UK CSAM3 action page, checked 23/08/2026. The rest is arithmetic on those figures.

Step two: what the action is worth after seed. Taking the annualised seed cost off the payment leaves £147.33 a hectare a year, before cultivation and drilling.

Step three: what the ground would otherwise return. Gross margins per hectare for England, non-organic, in the 2023/24 crop year. Variable costs have already been taken off these figures, so there is nothing further to deduct.

Source: Farm Business Survey, Crop Production in England 2023/24, Rural Business Research, England, non-organic, 2023/24 column, checked 02/08/2026. The winter wheat figures come from a sample of 572 farms.

The agreement runs three years, so the comparison has to run three years too, and that ground will not be in wheat for all three of them. Three rotations, worked from the crop figures above:

Source: arithmetic on the crop gross margins in step three, from the Farm Business Survey, Crop Production in England 2023/24, checked 02/08/2026. These three are illustrations. Work your own out from the same crop figures.

Step four: the gap.

Source: the payment rate at the top of this page less the seed cost in step one, set against the rotation averages in step three. The remaining figures are subtraction.

The rest of this section is Tilth's own reading of the arithmetic above. It is not scheme guidance and it is not sourced from Defra or the RPA.

Two things to set against the rotation figures. The survey reports one winter wheat figure, not first and second wheat separately, so a rotation with two wheats in it carries a second wheat at the same gross margin as the first. We have not found a published split to cite, so we have not applied a discount of our own invention. And it is a single crop year, and not a strong one: the same report's 2022/23 column put winter wheat's gross margin at £1,570 a hectare against the £988 above for 2023/24.

But that gap is missing the output, and on this action the output is the point. Unlike a fallow, a herbal ley produces grazing and forage, and the action is written on the basis that you will graze or cut it. What that is worth depends on whether you have stock, whether you can let the keep, and what you would otherwise be buying or growing to feed them. We have not found a published figure for the value of herbal ley grazing that we would put on a page about money, and we are not going to invent one.

Where that leaves it. On a pure arable farm with nowhere for the forage to go, the payment is the whole return, the gap above is the gap, and it is a wide one. On a farm with stock, or with a neighbour who wants the grazing, the payment is a top-up on an enterprise that stands on its own, and the comparison against an arable rotation is answering the wrong question. Both are legitimate readings of the same action, and which one applies to you is not something a website can know.

Does it work, and what makes it work better

This section is what we have found in published sources about the practice this action pays for. It is not scheme guidance, it is not Defra's or the RPA's view, and it adds no requirement beyond what the GOV.UK action page sets out. We have named every source and given the date we checked it. What it means for your ground is your decision.

This is one of the least evidenced actions on this site, and the fit is awkward as well, so both go first.

Conservation Evidence hold three assessments that touch a herbal ley and none of them is one. Create rotational grass or clover leys is about grass and clover rather than herbs. Incorporate leys into crop rotation is about converting arable to grass or legume pasture. Increase the use of clover leys on farmland is about clover, and it sits in their Bee Conservation synopsis rather than the Farmland Conservation one we use on the rest of these pages. CSAM3 requires grasses, legumes and herbs or wildflowers together, and we have not found an assessment of that.

The three graded assessments. Conservation Evidence, based at the Department of Zoology at the University of Cambridge, summarises the published studies behind individual conservation actions and has independent subject experts score each one. Effectiveness scores only the size and direction of the reported effects, and they say themselves it does not consider the quantity or quality of the studies. Certainty is the separate score for how many studies there are, how well built they are and how much ground they cover.

Creating rotational grass or clover leys comes out in their category Unknown effectiveness with limited evidence, on 3 studies, with 0 per cent for effectiveness, 10 per cent for certainty and harms not assessed. That certainty score is the lowest we have recorded anywhere.

Incorporating leys into a crop rotation comes out as Trade-off between benefit and harms, on 1 study, with 46 per cent for effectiveness, 45 per cent for certainty and 36 per cent for harms. That category is the first of its kind on this site. Every other action we have written up has come back as Beneficial, Likely to be beneficial, Unknown effectiveness or No evidence found. A trade-off means the panel judged there to be real harms alongside the benefit rather than none worth scoring.

Increasing the use of clover leys is Awaiting assessment, on 2 studies, with no scores against it at all.

Source: Conservation Evidence, action 643, Create rotational grass or clover leys, and action 900, Incorporate leys into crop rotation, both Farmland Conservation synopsis, and action 16, Increase the use of clover leys on farmland, Bee Conservation synopsis, all checked 22/08/2026. Cite the first two as Dicks et al. (2020), Farmland Conservation, pages 283 to 321, in What Works in Conservation 2020, Open Book Publishers.

What the studies found. On the leys themselves, a controlled study in Finland found clover leys held more spiders and fewer pest insects than a barley control plot. A UK study found one-year ley plots carried significantly lower earthworm species richness and abundance than leys that had been down three and a half years. A replicated UK study comparing ten conservation measures found grass leys held fewer plant species than the other nine.

On leys in a rotation, the single study behind that assessment is Danish, on a sandy loam. It found that reducing the extent of grass pasture in the ley reduced the undesirable uptake of nitrogen by the grasses, and therefore lowered the rate of fertiliser needed for the crops that followed.

On clover and bees, Conservation Evidence state plainly that they have captured no evidence that increasing the use of clover leys enhances wild bee populations. In one German trial, four bee species nested in reed stem bundles placed in set-aside sown with a clover and grass mix, including one endangered species, but three of those four also nested in stems placed in barley fields. In the same study, 12 bee species nested in stems placed in two-year-old set-aside mown in late June and 16 in old meadows.

The second study behind that assessment is about cutting. Fluri and Frick rotary mowed flowering white clover in Switzerland, with and without a mechanical processor fitted, the sort that crushes the mowings to speed drying. With the processor, between 53 and 62 per cent of the foraging honey bees recorded before mowing were found injured or dead.

Conservation Evidence say themselves that studies are not directly comparable or of equal value, and that study size, design, reported metrics and relevance to your own situation matter more than "simply counting the number of studies that support a particular interpretation".

Source: Conservation Evidence, actions 643, 900 and 16, key messages and supporting evidence from individual studies, all checked 22/08/2026.

What we have not found. Nothing on a multi-species ley with herbs in it, which is what this action requires. Nothing on soil structure, soil carbon, soil biology or drought resilience, which is what the GOV.UK page says the action is designed for, because Conservation Evidence is a wildlife database rather than a soils one. And no published figure for the value of the forage, which is the number the money section further up this page also declines to invent.

What the sources say makes it work better. All of the following comes from the studies listed on those Conservation Evidence pages, and it is a description of what was found rather than advice from us.

On composition, the Danish study is the only thing we have and it points at the grass fraction. Less grass in the ley meant less nitrogen taken up by the grasses and less fertiliser needed on the following crop.

On time, the earthworm finding is the only measure of a ley at different ages that we have found: one-year plots came out significantly below leys that had been down three and a half years, on both species richness and abundance.

On cutting, Fluri and Frick's result is the most directly usable thing in this section. Mowing white clover while it is in flower with a processor fitted to the mower killed or injured well over half the foragers that had been recorded on the plot beforehand. Taking the processor off reduced that.

Source: Conservation Evidence, actions 900, 643 and 16, supporting evidence from individual studies, checked 22/08/2026.

What follows is Tilth's own reading of how those findings sit against this action, and it adds no requirement beyond what the GOV.UK action page sets out.

The nitrogen finding is the one we would take away, and it sits awkwardly against the action. CSAM3 requires grasses, legumes and herbs together, and the GOV.UK page says the action is designed to produce forage with minimal use of inorganic fertiliser. The only study behind the ley-in-rotation assessment found that the more grass there was in the ley, the more nitrogen the grasses locked up, and the more fertiliser the following crop then needed. That is one study, on one soil type, in Denmark, and we would not build a decision on it. But it is the reason that assessment carries a trade-off rather than a clean benefit, and anyone doing this action for the nitrogen should know the finding exists.

The cutting finding and GOV.UK's own advice agree, which is worth saying because the advice on the page has no reason attached to it. GOV.UK suggests, as advice rather than a requirement, resting the ley from grazing or cutting for at least five consecutive weeks between early May and late July. That is the flowering period. Fluri and Frick supply the reason: mowing clover in flower with a conditioner on the mower killed or injured more than half the bees working it. If you do cut inside that window, the specific thing their study points at is the processor rather than the mowing.

The age finding cuts against something this action requires, and it is worth setting beside the same point on the legume fallow page. Earthworms were significantly better under a three-and-a-half-year ley than a one-year one. CSAM3 makes you re-establish before the third year, which resets the ley. On CNUM3 the re-sowing rule matched the evidence, because a legume mix collapses by year three. Here it may run the other way, because the one thing measured over time was still improving. We would not claim that as a finding about herbal leys, since it is a single study on grass and clover, but it is the sort of thing worth watching on your own ground.

And the honest summary is that this action is asking you to take arable ground for three years on about as thin an evidence base as anything on this site. Three assessments, one scoring zero for effectiveness, one a trade-off resting on a single Danish study, one awaiting assessment altogether, and nothing at all on the soil aims the action is named for. That is not a reason to avoid it. Plenty of farms have their own reasons for a herbal ley and the forage is real. It is a reason to be sceptical of anybody who tells you confidently what one will do for your soil.

What you actually have to do

Establish a herbal ley from a seed mix containing at least one grass species, at least two legume species and at least two herb or wildflower species. On land at risk of erosion, use establishment techniques that minimise soil erosion and runoff. Once the ley is established you must maintain it, which GOV.UK puts as managing it in a way, and for a period of time, that can reasonably be expected to achieve this action's aim. You must also minimise the use of inorganic fertilisers containing nitrogen, which GOV.UK says will usually be no more than around 40 kilograms of nitrogen per hectare per year.

GOV.UK's advice section suggests a considerably richer mix than the minimum, in the region of five grass species, four legume species and four herb species, and suggests resting the ley from grazing or cutting for around at least five consecutive weeks between early May and late July. That advice is explicitly not part of the requirements. The requirement is the one grass, two legumes and two herbs or wildflowers.

Establish the herbal ley by early autumn, within 12 months of the action's start date. Maintain it in the same place for a period of time that can reasonably be expected to achieve this action's aim, which GOV.UK says will usually be the end of the second summer after sowing. Re-establish it by early autumn, at the same location or a different one, and maintain it to the end date.

Source: GOV.UK, CSAM3 action page, checked 02/08/2026.

What you cannot do on it

Do not use the established ley for storage. Do not apply pesticides to it, except herbicides to weed wipe or spot treat to control injurious weeds, invasive non-native species, nettles or bracken, and except herbicide used to destroy an existing ley in order to re-establish it. Use of inorganic fertilisers containing nitrogen must be minimised, which GOV.UK says will usually be no more than around 40 kilograms of nitrogen per hectare per year.

Source: GOV.UK, CSAM3 action page, checked 02/08/2026.

Where it can go

Agricultural land below the moorland line, on arable land growing crops, temporary grassland (TG01), arable fallow (FA01) or improved permanent grassland (PG01). It can be rotational or static.

Two hard exclusions. GOV.UK says you must not enter any area designated as an SSSI into this action, and you must not enter any area with an historic or archaeological feature into it either. Both are stated as ineligible rather than as consent or notice requirements.

Source: GOV.UK, CSAM3 action page, checked 02/08/2026.

Things worth watching

This section is Tilth's own reading of where this action is easy to get wrong. It is not scheme guidance, it is not sourced from Defra or the RPA, and none of it adds a requirement beyond what the GOV.UK action page sets out.

The requirement and the advice are different numbers, and they sit close together on the page. One grass, two legumes, two herbs or wildflowers is what you have to do. The five, four and four in the advice section is a suggestion, and GOV.UK says so. Reading the advice as the rule makes the action look more demanding and more expensive than it is; reading the rule and ignoring the advice may make for a poorer ley.

The herb species are the part to count. A mix can be sold as a herbal ley on the strength of its grasses and clovers. The two herb or wildflower species are a stated requirement, so the composition on the bag is the thing to check rather than the name on it.

Two sowings, not one. The timing puts an establishment and a re-establishment inside the three years, so budget the seed twice. On the merchant price used above that is the difference between £115 and £230 a hectare across the agreement.

The nitrogen requirement is a judgement with a number attached to it. GOV.UK asks you to minimise inorganic nitrogen and says that will usually mean no more than around 40 kg a hectare a year. That is not a hard cap in the way a date is a hard date, but it is a figure attached to a requirement, and 40 kg is not much on ground you are trying to get forage off.

SSSI and historic features are outright exclusions here. On AHW7, CIPM3, CIPM4 and CNUM3 those are consent or HEFER requirements you can work through. On this one the page says the land is ineligible. That is a different answer and it is worth reading twice before planning round it.

The forage is part of the return, and only you can value it. The payment on this action sits well below CNUM3's for a legume fallow on the same kind of ground, and the visible difference between the two actions is that this one lets you take something off. If you have no use for the forage, the payment is the whole of your return and the gap above is the gap.

The merchant prices above were read inclusive of VAT. Merchant sites can display either basis, and a quote you are given may be on the other one. Worth settling before the figures go into a budget.

Keeping the evidence

Also Tilth's own reading. GOV.UK sets the requirements; what follows is a practical suggestion about record keeping.

The action page asks for evidence of what you have done, with field operations at parcel level and their invoices, and photographs or other documentation, given as examples.

The two seed invoices with their full species breakdowns speak directly to the composition requirement, because the one grass, two legumes and two herbs condition is a claim about what went in the ground and the invoice is the paperwork that records it. After that, the fertiliser record for the parcel is worth keeping deliberately rather than incidentally, since the nitrogen requirement is one of the few places in the action where a number is attached to what you do. Grazing and cutting records are worth having for your own sake as much as anything, since they are what tells you whether the ley is earning its place, and photographs across the season make a case that a February picture on its own does not.

The part only your own ground can answer

The gap above is worked against an arable rotation on national figures, which is the right comparison only if the forage has nowhere to go. What the keep is worth on your farm, and what this particular block returns in cropping, are both numbers that live in your own records rather than in a national survey. Tilth is where we keep them, field by field. Request an invite.