Some thoughts on grassland management for Butterflies, long grass is not always bad.

Some Butterflies are dependent on shrubs and trees as larval food plants. The larval food plants for the others are herbaceous plants, some such as Garlic Mustard, Honeysuckle and various Violets growing in lightly shaded woodland and their margins but most herbaceous food plants grow out in the open more or less surrounded by grasses - that is to say in grassland. Sooner or later unmanaged grassland in this country usually becomes swamped out by a natural succession of small shrubs and then trees and the low level larval food plants die out. On more fertile soils unmanaged grass can build up a thick straw-like layer of dead grass at soil level, changing the species-mix of the grassland. This can take several seasons and does not have to be removed every year.

Ignoring the 'green concrete' of amenity grassland and lawns where flowering plants are regularly killed off in the persuit of neatness, and farming leys (short term grass crops from seed), that leaves permanent pasture managed for grazing and hay, roadsides and sites managed for wild life.

BRIEFLY, there are two main grassland management systems:

1. Grass cut or grazed to protect low growing plants from being swamped by taller grasses, nettles etc. (includes hay meadows).
Advantages: this is good for low growing larval food plants, especially those on poor chalky soils, and for many other spring and early summer flowers.
Disadvantages: this removes tall, late summer nectar flowers on fertile soils. It kills any the eggs, larvae and pupae of any butterflies present (Skippers in grass, Peacocks etc on nettles) above the level of the cut at the time.

2. Seldom cut/grazed grass (except where necessary to remove scrub).
Advantages: this leaves tall plants to provide nectar though late summer. This is good for the butterflies whose eggs, larvae and pupae would have been killed by cutting the grass and any taller legumes such as Field Pea also present.
Disadvantages: in some places low growing plants may be swamped out by the long grass and some desirable grasses can be gradually excluded by a thick straw-like layer of dead grass at soil level. See Roseland House paddock.

Choice of system:

Some sites are more suited to one system than to the other.

On poor calcareous soils a cut or grazed regime is the natural choice to protect the low growing native wildflowers including several essential butterfly foodplants including Horseshoe and Kidney Vetches, Rockrose and Sheep's Fescue. On other poor soils a summer 'hay' cut can encourage flowering plants, the removal of the 'arisings' helps by lowering the soil fertility which would otherwise encourage the lusher competing growth.

On poor sandy heathlands cutting with or without grazing is usually necessary to prevent scrub invasion. This is usually managed in a cycle, cutting a different portion each year. This allows old woody heathers to become refreshed with new growth, and restricts brambles and tree invasion. In some places chemical control has been successful against Bracken invasion.

On more fertile, non calcareus soils where the priority is not for spring flowers and calcareous specialists would not grow anyway, a case can be made for less frequently cutting or grazing. This is not a very common habitat apart from strips of field and road margins, and provides a haven for the butterflies dependent on the more robust grasses and associated plants. I have noticed in spring how much the ground layer of tussocky leftovers is used by Bumble Bees as they commute to and from the nearby Sallow flowers. In its early years grassland converted from arable is less dense than ancient permanent pasture, and sites next to woodland can initially produce a dense crop of tree seedlings.
A good compromise between killing butterflies as immature stages living in the grass (by cutting too often), and losing their favourite food plants (by not cutting enough) would be to cut short enough to remove the basal thatch or to graze with cattle as and when necessary or at about once every four years in rotation one quarter at a time.

On more fertile, non calcareous soils where there is a particular priority for the more interesting spring flowering plants, such as Cowslips, Oxlips or Orchids cutting will be needed - as in hay meadows, and similarly removing the hay lowers soil fertility. A wider range of wildlife would be catered for by allowing a portion of the site to be permanently uncut.

What not to do. Cutting the grass once or twice a year when butterfly life cycle stages are at risk, and where there is no scrub invasion, depriving the butterflies of late nectar and the birds of seed.

Fine tuning areas of seldom cut grass.

Controlling trees and shrubs. Invasive growth from Blackthorn hedges and other scrub will need to be cut as and when it occurs. Tree seedlings such as Oak, and Alder can also be a problem, as well as overlarge patches of nettles.

Nettles are host plants for numerous insect species including several Butterflies - and some nettle patches are welcome in an area which is predominantly uncut grass. On reasonably fertile soils these patches expand slowly year by year and usually need some control. Spraying the edges with herbicide will slow them down a little, but a better solution is to mow paths round any nettle patches which are getting too big.

Introducing other food plants. Privet is one of the best plants to add for nectar. It produces masses of small white flowers in July at about mid-season for Meadow Browns and Ringlets, and is much favoured by bees. Sorrel has established here from seed, but most of the clover has been swamped out and I have not successfuly introduced Bird's Foot Trefoil. Taller legumes may do better in longer grass. Meadow Pea, Lathyrus pratensis is already present here and may be added to and a few other Vetches tried. In boggy areas Water Mint and Hemp Agrimony are excellent for nectar, and already present at Roseland House.

Introducing other nectar plants. Given the invasive habits of Thistles, Knapweeds may be a more suitable nectar plant for late summer pasture. The advantage of the Thistles is that they flower in time for the main flight season of our most common species, and Knapweed comes into flower a few weeks later, covering the later part of the season.
Thistles are excellent nectar plants in long grass but they should not be allowed to spread to other property.

Preventing the spreading of weeds. Under the Weeds Act, 1959, the Minister has the power to require any particular occupier of land to prevent the spread of certain weeds. The Act applies to Spear Thistle, Creeping Thistle, Curled Dock, Broad-leaved Dock and Ragwort. The wind blown seeds of Thistles are most likely to be a problem. Here a topping cut in mid to late August as the flowers go over may be sufficient to prevent spreading by seed. A high topping cut would inflict minimal damage on any other wild life in the grass at that time.

Safe cutting times for some local species in long grass:

Reference to the sightings table suggests that in this area a cut not later than the third week in July will kill the least number of Essex Skipper and Gatekeeper eggs. This also suits Large Skippers, Meadow Browns and Ringlets.

Small Skipper. The food plant is Yorkshire Fog, a common grass in older pastures, and possibly other soft grasses.
Safe cutting period: none. From the time of the adult flight period in July to mid August there is no completely safe cutting period as eggs, caterpillars and chrysalises are all found on the grass leaves and stems continuously until the start of the following flight period. The caterpillar emerges from the egg in late summer and hibernates inside a grass sheath. It feeds to full size in spring and early summer before forming a chrysalis. There is least risk from cutting in the chrysalis stage in June as chrysalis is found in the base of the grass clump and a fairly tall cut could pass over it. It would not be easy to predict this 3-4 week gap as seasons can be up to 2 weeks earlier or later than usual.

Essex Skipper. The main food plants are Cocksfoot and Timothy, both common in permanent pastures.
Safe cutting period: none. The eggs are present on the stems or furled leaves of grass from the adult summer flight period, until they hatch in spring. Then they are present on the grass as a caterpillar until midsummer before forming a chrysalis at the base of the grass. As with the Small Skipper there is a period of least risk from cutting, unless cutting short, during the chrysalis stage which for this species is a week or two later. (Not that you would probably want to cut in June anyway).

Large Skipper. The main food plant is Cocksfoot, a common grass in this area.
Safe cutting period: none. Eggs are laid on the grass during the July (or in an early year, June) flight period. The caterpillars are either feeding or hibernating on the grass until forming a chrysalis at the base of the plant from about mid May to mid June. As with the Small Skipper there is a period of least risk from cutting, unless cutting short, during the chrysalis stage which for this species is a 3-4 week period in May to June depending on the season.

Small Copper. The main food plant is Sorrell.
Safe cutting period: none. With three broods a year and egg, caterpillar and chrysalis all on the food plant. The least unsafe method of cutting would be to cut above the basal leaves, and not to cut the whole site all in the same year. Sorrell seems to be resistant to overcrowding by uncut grass.

Brown Argus. The main food plant is Rock Rose, or on non calcareous soils Cut-leaved and other Geranium species.
Safe cutting period: late April to late May when the Chrysalis is on the ground. With the overlap of broods it would not be so easy to pick a safe time when the second brood chrysalis is on the ground and other stages not on the food plant. Where cutting is essential it would be safer if not too short. The cut-leaved Geranium can decrease in denser grass.

Common Blue. The food plants are legumes, both tall and short. Where it is not crowded out by dense grass, Bird's Foot Trefoil is a favourite. Otherwise it be worth adding to existing taller plants such as the Meadow Pea, or introducing others such as Rest Harrow.
Safe cutting period: not much. There is a potential safe slot when the chrysalis is on the ground in May, depending on the season, but after that there is a good chance of eggs or caterpillars being on the food plant. It may be possible to cut above the shorter food plants like Bird's Foot Trefoil, but not the taller Vetches. These are best cut on just one part of the site at a time per year, if at all.

Speckled Wood. The food plants include Cocksfoot, Yorkshire Fog and other grasses.
Safe cutting period: none. Caterpillars and eggs are on grass leaves more or less continuously all year. They can hibernate either as caterpillars or as chrysalises contributing to a blurring of the generations in the following year. These are best cut on just one part of the site at a time per year, if at all.

Gatekeeper. The food plants are a wide range of grass species.
Safe cutting period: June (when the chrysalis is on a shrub) varying a little with the earlyness of the season.
The eggs and caterpillars are on grass from late July to the following May, when they leave the grass to form a chrysalis on a nearby shrub.

Meadow Brown. The food plants are a wide range of medium to fine leaved grass species.
Safe cutting period: none as the egg, caterpillar and chrysalis are all on grass. The least unsafe period would appear to be late June to early July a few weeks into the flight period when there are enough adults hatched to lay their eggs after the cut. Higher cuts would have less risk of killing any unhatched chrysalises still attached to the grass.

Ringlet. Food plants: “Cock's Foot and False Brome are favourites, but only where these coarse grasses grow as lush, uncropped tussocks”. Jeremy Thomas in Thomas and Lewington. (2010).
Safe cutting period: June. The egg and caterpillar are found on grass leaves but the chrysalis is formed at the base of the tussocks beyond the reach of a reasonably tall cut. Ringlets overwinter as caterpillars, spending most of June as a chrysalis so that is the ideal time to cut if necessary - or as with the Meadow Browns this can be stretched into early - mid July and aligned with the start of the flight period when most of the eggs are still to be laid.

Small Heath. The food plants are fine-leaved grasses.
Safe cutting period: anytime, as long as you cut above the majority of the fine leaved grasses. The egg, caterpillar and chrysalis are all on grass so there is no totally safe period for a very short cut. The least unsafe period would appear to be late May to early June a little way into the flight period when there are enough adults hatched to lay their eggs after the cut. Higher cuts would have less risk of killing any unhatched chrysalises still attached to the grass.
The finer leaved grasses are also dwarfer plants and favoured by measures to reduce competition from stronger species. At Roseland House different species have established dominance in different parts of the paddock possibly due to varying soil fertility and water seeps without any selective intervention.