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Establishing grassland and increasing botanical diversity at existing sites

Grass by Amy LewisGrass by Amy Lewis

Grassland surrounded by different habitats such as hedge, scrub, woodland and even bare ground can support a rich community of wildlife. The creation of new grassland habitat complements the conservation management of existing grasslands.

But selecting the most appropriate method of grassland establishment can be confusing – and expensive. The following sections and tables summarise your key considerations and options for establishing grassland on ex-arable bare land  and for increasing the botanical diversity of existing grassland.
 

Grass seeds by Bill StevensonChoosing seeds

Suffolk’s grassland flora has a distinct genetic makeup. Indigenous plant communities and the species they support have adapted to the local soil, climate and management conditions over hundreds of thousands of years.

In order to protect the genetic diversity of Suffolk’s native grassland and maintain regional diversity, grassland creation or restoration projects should, wherever possible, use local provenance seeds i.e. seeds collected from native wildflowers in Suffolk.

Local provenance, East Anglian native grass and wildflower seed mixes are in short supply. The majority of grass seed supplies currently originate from North America or Australasia and many wildflowers have been cultivated and developed as agricultural fodder plants. Such plant material may superficially look like our own plants but, as well as diluting our own genetic wild plant diversity, subtle differences in their structure mean that some varieties cannot be used by insects. For example, certain bumble bees are unable to feed on cultivated strains of red clover, and the common blue butterfly larvae will not feed on foreign bird’s foot trefoil.

Grassland establishment on bare land

Before any other work is started, it is vital to establish the most important characteristics of the site – the soil type, fertility, dampness and existing flora and fauna on and adjacent to the site. These characteristics will influence your method of establishment and ground preparation.

Wildflower establishment is best achieved on soils where nutrient levels (especially phosphate, potassium and nitrogen) are low and where competition from coarse grasses and dicotyledonous weeds is low. Ex-arable land will be high in nutrients.

Whilst natural regeneration to create a flower-rich grassland is usually not an option on heavy land, it might be considered as the first option for light land sites and very small sites on impoverished soil surrounded by a good seed source, such as new pond edges or where a building has been removed. It is, however, the cheapest and most practical option for creating valuable rough cover.

Fritillary by Bill StevensonFor most heavy land sites, the best option for Suffolk’s biodiversity (and probably the cheapest) would be to establish grassland using species-rich green hay from a local donor site. For small sites, scattering ripe seed collected by hand from local species-rich verges or meadows onto a prepared seedbed is a simple but often effective option.

Remember use local seed wherever possible. This is best for wildlife and most likely to succeed. More expensive and difficult, but a good alternative, is to source a local provenance seed mix and establish grassland using a conventional method e.g. drilling or broadcasting into a well-prepared seed bed. The least desirable, and potentially harmful, option would be to use an expensive ‘off the peg’ seed mix containing non-British seeds.

See the table below for a summary of methods, considerations and management pointers for establishing grassland on bare land.

Methods and considerations for establishing wildflowers on bare land

Method and key
considerations

Key establishment management points

Comment on resulting grassland

Natural regeneration

Often the most
appropriate method for light soils.
For very small, impoverished soil sites near species-rich areas.

Allow plants to regenerate but top regularly (2 to 4 times in spring and summer) in the first two years to increase grass tillering and sward establishment, and reduce annual and perennial weed problems.

Over several years of appropriate grazing or cutting, the established grassland will reflect the species found in nearby grassland.

Early thistle and ragwort problems may need spot treatment.

Seed with locally
harvested seed


Harvest seed from a local flower-rich site (e.g. roadside verge,
churchyard, unimproved
hay meadow).

If sowing directly into ex-arable land, establishafter harvest or undersow in a growing crop in the spring. Alternatively cultivate to create a good weed-free seedbed and drill or broadcast (hand or machine) seed in late summer or early autumn (well before frosts). Roll afterwards to firm up.


Take a haycut the following year in June or July. Do not cut before unless there is an overwhelming weed problem (e.g. creeping thistle) in which case spot treat with glyphosate as soon as possible during the growing season.

Over a few years valuable grassland can be
created reflecting the local characteristic grassland type and maintaining local genetic diversity.

Some mobile insects and other wildlife which has adapted to the local donor grassland will colonise the grassland quickly. Less mobile species may take longer.

Seed with British native seed

Check origins of mixes

As above

Valuable grassland can be created
supporting a range of wildlife, but with less potential variety than above.

Introduce herb-rich green hay


Select donor site with similar physical characteristics (soil type, pH, dampness etc).

Harvest donor meadow at
optimum time for maximum seed catch i.e. late June to early July (check meadow timing for best harvest).

Check all the correct
permission is given to
harvest the site i.e. owners’ permission or discuss taking green hay with English Nature if it is an SSSI.

Prepare seedbed on recipient site. Cultivate to create a weed-free firm site.


Harvest donor site as big round bales and roll out all bales over recipient field within 24 hours (the sooner the better) to prevent heating up of bale. One ha of hay should be spread thinly over 2ha of the recipient site to avoid need for raking up and removal after 3 weeks. Loosen and scatter the rolled out bale using a rake, hay turner or muck spreader.

The following spring and summer cut repeatedly to minimise thistle and other weed problems
and to encourage the sward to tiller out. A light chain harrowing after hay is baled may encourage more seed germination. Then, if
possible graze the aftermath until March or until the site shows signs of poaching, ideally with cattle to create some variety in sward structure.

In the second and subsequent summers mimic the donor site’s normal hay meadow management (June or July).

This method seems particularly suited to the crested dog’s-tail-common knapweed
grassland (National Vegetation Classification MG5), a widespread but uncommon flower-rich meadow on neutral heavy soils managed as hay meadow.


Most species present in significant amounts from the donor site will establish in the new meadow, but some may take some years to do so. Indeed, it appears that hay strewing over other methods seems to promote colonisation by orchids (I Trueman & P Millet in British Wildlife October 2003).


To maximise value for invertebrates, ensure as much variety in sward structure is created at the end of every year by leaving some areas uncut each year (up to one third) either as mid-field or field margin strips, rotated each year to avoid scrub encroachment at the margins.


Increasing the botanical diversity of existing grassland

A species-poor grassland site usually results from the site having been agriculturally improved at some stage to increase its grassland yield or quality (e.g. for silage,top quality hay, haylage or intensive grazing).

It's possible that the site may have been reseeded with agricultural strains of grasses, clovers and other legumes, and/or had fertiliser applied, which results in a few species thriving at the expense of the smaller, more delicate plants. The use of herbicides to reduce weed 'problems' such as thistle or nettle would also result in the loss of other broadleaved plants.

Re-introducing wildflowers to an existing sward is important, but it is not easy, particularly while soil fertility is still high.

Consider the following recommendations:

• Stop all fertiliser and herbicide applications and continue to graze hard or take silage, haylage or hay cuts to reduce soil nutrients. This may take many years and until soil nutrients are reduced, any method of establishing wildflowers will have limited success.

• Once soil nutrients have been exhausted or reduced, consider the options for introducing wildflowers outlined in the table below. But remember, be patient.

Methods and considerations for establishing wildflowers in existing grassland

Method and the key
considerations

Key establishment management points

Resulting grassland

Introduce herb-rich green hay

Select donor site with similar physical characteristics (soil type, pH, dampness etc).

Harvest donor meadow at
optimum time for maximum seed catch i.e. late June to early July
(check meadow timing for best harvest).


Method 1: For a reseeded sward of low botanical diversity
one method is to completely remove all vegetation on existing grass sward by herbicide (glyphosate) in late summer. Then follow method outlined in above.

Method 2: To avoid total vegetation removal of grass sward,
retain but cut very short or graze very hard prior to hay strewing and create sites for germination by harrowing, raking or discing.

After strewing hay put livestock on field after a week or so to poach the site, eat hay and aid germination
by digestion process.

For Method 1, see above

Method 2 is cheaper and less
disruptive for soil-dwelling
invertebrates but may not
achieve as good result as
method 1.

Rotovate and seed site with wildflower seeds

Ideally use seed harvested
from local species-rich site. Alternatively obtain British native origin wildflower seeds appropriate to soil and pH type.

Rotovate sward to open it up and broadcast seed (manually/
by machine) in early autumn.

The grass matrix will be reformed as many of the original grasses regrow. Regular cutting (and removal of cuttings) may be required between April and October to prevent vigorous grass growth blanketing the slower establishment of wildflower plants.

The following year manage by hay cutting, but delay grazing for two years or so to allow good root mats to establish.

 
Slot seeding site with locally harvested seed

Ideally use seed harvested from local species-rich site. Alternatively obtain British native origin wildflower seeds appropriate to soil and pH type.

Ensure existing grass is cut short or grazed hard prior to seeding in early autumn.

Using a Hunters seeder, rotovate 10cm strips into existing sward.

Using a Stanhay or Gibbs drills seed (2kg/ha bulked up by sand or barleymeal) and spray glyphosate herbicide along the seeding ‘slot’ or strip.

Cut grass the following year whenever it exceeds 5cm to help reduce competition of establishing plants and to encourage good growth of root systems but avoid ‘scalping’ turf.

The following year manage by hay cutting or grazing.

Over a few years valuable
grassland can be created,
especially if local provenance
seed is used helping to
maintain local genetic diversity.
Mobile wildlife will colonise
quickly.
Introduce wildflower plugs, pot grown plants or turves dug from a species-rich site

Useful for small sites and where the early visual appearance of the site is important.

Ensure existing grass is cut short or grazed hard prior to planting.

Do this in early autumn or, less ideally, in spring providing the soil is damp (but not frozen).

To reduce competition from existing sward, spot treat areas
with glyphosate to plant groups of plants or remove turf. Areas to treat and numbers to plant will depend on budget or turf size. The more plugs or larger turves planted, the greater the success!

A recommended planting density is 2-9 plants per m². Due to their small rootstock, plants and
turves may need additional watering, especially on lighter
land. The following year manage by hay cutting or grazing.

Useful for introducing plants
which do not establish easily
from seed in mixes or those
that produce little seed in
cultivation but easily reproduce
vegetatively.