Diversifying existing grasslands

Altering the management of existing grasslands may encourage diversity. Changes can be made by reducing the frequency of mowing, by stopping fertiliser treatment, and by various mechanical procedures such as raking or scarifying. However, diversity will only result if additional species are already on the site, or able to colonise. Species on the site may be present as seeds in the soil, or as plants which are not able to flower due to mowing. The most likely sites are ‘poor ’ grasslands on well-drained soils which tend to be gappy and brown in dry summers. Grass growth will be less competitive than on more fertile sites, and a break in mowing will allow plants to flower and seed into gaps. Other species may colonise, especially if there is a good seed source nearby.

Many urban sites however will not diversify through simply reducing mowing. Often the soils are too fertile, or lawns, parks or sports turf may have been fertilised for many years. These sites can only be diversified by seeding or planting additional species, and by carrying out an appropriate management regime to allow them to establish and spread.

Seeding

Simply scattering seed onto an existing grass sward will have no effect, as the grass sward will be too dense to allow germination and establishment. Gaps must be made first in the grass sward. Raking or scarifying will not be enough, as this will only remove the dead grass ‘thatch’, and stimulate the grass to renewed growth. Gaps can be made by removing turves, or by using a herbicide.

Depending on the size of the site, you would normally need to remove an area of turves at least 1m square. If you have suitable infill material of sandy subsoil, seed-free topsoil or crushed concrete, this can be used to replace the turves provided the pH of the infill is suitable for the site. If not, any species that do survive on the introduced patch are unlikely to spread. Alternatively, remove the turves and put to one side, and dig out the soil to about a spit deep. Place the turves upside down in the bottom of the pit, and then cover with the remaining soil. Try and invert it so that the soil from the bottom of the pit, which is likely to contain the least weed seeds and be least fertile, finishes at the surface. Where the topsoil is shallow, the subsoil can be easily dug out and used at the surface.

To avoid a ‘checkerboard’ effect, vary the shape and size of the patches, and scatter them randomly.

This is obviously labour intensive, and it may be easier to use a herbicide. A glyphosate herbicide will kill grasses and broadleaved plants, and can be applied at any time of year when the plants are growing. For optimum wildflower seed establishment, use the herbicide in August, to allow the sward time to die off before seeding in September. Rake off the dead material and rake the surface before seeding.

On large sites, slot seeding can be carried out using agricultural machinery, which sows directly into existing grass swards. For further details see Wildflowers Work, Landlife (1994).

Planting

Germination and early establishment of wildflowers can be carried out in a nursery, and the plants then planted out into the sward. This method is obviously more expensive and time consuming than sowing in situ. It is best used for species that are slow to germinate, establish and flower. This process can be speeded up by using pot- grown plants, which will themselves then produce seed to colonise bare patches.

As an alternative to pots, small plants grown as ‘plugs’ can be used, which reduces the cost. However, their small root-ball means that establishment is tricky, and watering will be needed in dry spells.

Pots or plugs will establish best on patches of bare ground, produced by removing turf or applying herbicide. Cultivating the ground to a shallow spit’s depth will encourage the roots out of the root ball. Weeding is necessary for the first season at least, as cultivation will also encourage weedy growth. Pot grown plants and plugs of slow-growing species can be used in combination with a seed mix on bare ground.

The activity of growing plants in a nursery and planting them out is a very satisfying activity for schools and other groups.

Suitable species for plants and plugs are listed below. Annuals, and easy to grow perennials such as ox-eye daisy are not worth growing in pots, but should be sown direct.

Management regimes

The following three management regimes can be used for new or long established grasslands. The regime must be suitable for the species chosen or found on the site, to allow flowering and seeding, and to favour selected species. Once embarked upon, the same regime should be followed in the long term, to allow the site to develop its own particular character and range of species. However, there must always be some compromise between the requirements of the diversity of grassland flora and fauna which a site might support. For example, even taking a small selection of butterflies, a range of different sward heights and cutting times would be necessary to support them. Different interest groups will have their own ideas of what the priorities should be for a site. The unexpected arrival of a particular species of plant or animal may change priorities, and the vagaries of the weather also play their part. Whilst having clear aims for a site, there must also be flexibility to adapt as circumstances change.

On larger sites, the management regimes described below can be applied to different parts of the site. Corners, edges and other areas can be left uncut as invertebrate havens, and then cut back as necessary on rotation to prevent them going over to scrub.

Flowery lawn

Some flowering perennials are adapted to close-mown conditions and frequent trampling. A few weeks without mowing during May and early June will allow a colourful flowering period. The plants are the typical ‘weeds’ of lawns, such as daisy, plantain, cat’s ear, speedwell, clover and bird’s foot trefoil. During the rest of the growing season, mow every two weeks, and remove the cuttings. Don’t use any fertiliser. This treatment is ideal for areas which need to be kept reasonably short and tidy.

Spring meadows

A cut in late spring follows the traditional pattern of cropping for hay, and allows time for a range of flowers and grasses to flower and set seed. Timing will vary with location and site, but will normally be in May. On recreation sites, it can be timed to allow a week or so for the site to ‘green up’ before it’s used for ball games, camping and so on. On larger sites, the grass can be cut for hay by a commercial operator. On smaller sites, haymaking can be done by hand as a community activity. Where vandalism and arson are a problem, it’s easier and safer to remove the crop as it’s cut. Use a forage harvester on larger sites, or a rotary mower with grass box for small areas.

Summer meadows

A late-summer flowering meadow is characterised by tall species, attractive to many butterflies. Cut the meadow regularly throughApril, May and June to discourage coarse grasses becoming dominant, and remove the cuttings. From the end of June, leave the meadow uncut to allow the growth and flowering of species such as knapweed, field scabious, hardhead and ox-eye daisy.