Seeding

Sources of seed

Commercial suppliers

Commercial seed companies are listed here. Note that some years a crop failure may occur, or a very large order for particular species be placed, which means that seed is not always available as listed by merchants. Some county wildlife trusts gather and sell seed from their nature reserves.

Local seed

Seed can be gathered locally from grasses and other flowering plants. This is slow and painstaking work, but it does mean that the seeds are of the same genotypes of the species that occur on that particular source. It is also a free source. Even if only a small quantity is gathered, the seed can be mixed with commercial supplies to improve the ecological value of the restored area.

Most seeds should be gathered during July, August and September, but timing will vary with species and locality. Grass seed can be collected by cutting the heads as they ripen, and leaving them spread on trays or paper in a dry place. The seeds can be shaken off when dry. Other plants may be more difficult, as the seeds on each head may not ripen simultaneously. The best method is to hold a plastic tray or container under the plant and gently shake the stem, or rub the seed head between the finger and thumb. This ensures that only ripe seed is collected, and there should then be no danger of depleting the natural stock. Always consult the statutory nature conservation agency or the local wildlife trust if there is any doubt over the wisdom of collecting any species which may be locally uncommon.

Leguminous seeds should be gathered just before maturity as the pods of some species explode and scatter the seeds. Gather the pods, and cover loosely to prevent the seeds being lost when the pods explode. Store seed in paper bags or cardboard boxes, but not in polythene bags.

Local groups or site managers may find it worth establishing stock plants of native species, in the same way that commercial seed companies operate. These stock plants are grown in a nursery in optimum conditions, and so can produce far higher yields than if competing in the wild. For example, one cowslip plant can produce 4,000 seeds (4.54g) in a season.

Live mulch

This involves raking existing turf, heath, scrub or woodland floor to gather a mulch of topsoil, plant litter, moss and plant fragments. This is then spread on the area needing revegetating at the rate of 1-3 litres per m2, and lightly raked into the surface (Bayfield and Aitken, 1992). The mulch will contain seed and plant fragments capable of rooting, as well as providing topsoil, organic matter and micro-organisms which aid establishment. The most successful use so far has been to combine live mulch with sown grasses to provide quick cover. Live mulch is unlikely to be successful in drought conditions. Little damage is done to the source area, though a light application of compound fertiliser can be given as required to speed recovery.

Hay and sweepings

Hay bales will contain suitable seed if cut from the type of sward you wish to reproduce. The seed can be extracted either by beating or trampling the hay over a sheet or clean floor, or the hay can be spread directly onto the site.

Sweepings from hay barns also contain seed, but should not be used on ecologically sensitive sites as they could contain undesirable agricultural strains. Seed merchants may give away sweepings but the species composition will be variable.

Heather

Fire-breaks are cut on many heather moorlands. If this is done in autumn, the cut material with its fruiting shoots can be gathered up and stored over the winter, and then spread over bare areas the following spring (Tallis and Yalden, 1983). Heather plants are slow-growing and in the first two years or so are very vulnerable to grazing,trampling or being buried or uprooted in unstable peat. The best method of establishment may be to sow a nurse crop of grasses, supported by fertiliser and lime, and then to spread the heather cuttings over this the following year. The heather grows up within the protection of the grasses, which decline as nutrient levels drop. Alternatively, brashings can be used (see below).

Soil seed banks

Most soils contain viable seeds, and some, at semi-natural recreation sites have been found to contain over 500,000 seeds per square metre. Seed banks tend to decline with altitude and trampling. In two different studies of a range of habitats in Scotland and the Yorkshire Dales, seed banks have been found to be dominated by rushes (Bayfield and Aitken, 1992). Bare peat usually contains no viable seed.

Trials suggest that the germination of seed and survival of the young plants can be encouraged by an application of fertiliser. Lime is also needed on acidic sites such as peat. However, trials have not been conclusive, and with infinite site variations, weather and other factors, outcomes are difficult to predict. For most small scale areas the best approach would seem to be to use a seed mix, with fertiliser and lime as necessary, rather than relying on the natural seed bank. The extra cost of seed on small sites is not significant compared to other costs. The normal priority is to get something growing to stabilise the site. However, on sites of special scientific interest, and other areas, there may be overriding reasons for not introducing any seed to the site. The example of Badbury Rings, shows how the simple method of collecting mole-hill soil provides a viable seed bank.

Soil stabilisation

Brashings

A simple, effective method to encourage the success of natural recolonisation or artificial seeding is to lay cut brashings of woody material over the eroded area. These stabilise the soil, trap wind-blown soil and seed, and provide shelter as seedlings grow up. The branches are also a deterrent to trampling and grazing. Any material can be used, but branches with a flat form of growth, such as larch, are more effective. On slopes and exposed sites, secure the brashings with pegs cut from suitable woody material.

Geotextiles

There is a huge range of materials, known as geotextiles, which are used for stabilising bare slopes, encouraging vegetation, and reinforcing existing vegetation against trampling. They are widely used in civil engineering for slope stabilisation, and especially on steep slopes at the sides of roads, railways and urban areas, and at water margins.

Their use for stabilising slopes on recreation sites, where trampling pressure is removed, have been mainly successful, and many types have been tried. Their main disadvantage is their cost, and the fact that they are easiest to use and disguise on regular slope profiles, which are common in civil engineering, but not on natural sites. Where the geotextile does not closely fit the slope, unsightly suspended sections of geotextile are likely to result.

Geotextiles suitable for erosion control and slope stabilisation on amenity sites are of two basic types; either a woven net, or a three-dimensional mat.

Woven net is available in jute, coir or synthetic materials such as polypropylene or wire. Jute and coir have the advantage of being natural, biodegradable, and drape closely over irregular slopes.

Jute is able to absorb up to five times its own weight in water, which lessens initial run-off, and provides a moisture reserve for plant growth. Jute mesh typically covers 35-40% of the soil surface, providing shade, insulation against temperature extremes, and maintenance of humidity, whilst not inhibiting plant growth. The cellulose fibres become incorporated into the soil as the material decomposes, improving long-term resistance to erosion. The mesh is secured with wire staples that rust away within five years or so. Seed can be sown before or after the mesh is laid on the slope, and shrubs or trees can be planted through it. Jute is biodegradable within two to five years in lowland areas, giving sufficient time for vegetation to stabilise. However, in the uplands and mountains jute only lasts about one year, which is not long enough for vegetation to establish, and the site is likely to be further disfigured by tatters of fabric blowing in the wind. The pale colour is also much more noticeable from a distance than dark or black materials. Brands of jute mesh include Soil Saver (Hy-Tex Ltd.) and Geojute (Ardon International). They weigh about 500g per square metre. The UK market leader jute mesh, Soil Saver, costs about 65p per square metre, including the fixing pins (1995 price).

Coir (coconut fibre) geotextiles last between four to ten years, which is double the life of jute. They have a greater tensile strength, and are heavier for the same mesh size. Coir is suitable for steep or severe sites, or where plant establishment is expected to be slow. Coir geotextiles are available in a range of mesh sizes, from the suppliers given above for jute.

Polypropylene and wire mesh geotextiles are described here. Some types have been used successfully for laying over existing grass or into new grass paths to provide surface reinforcement against trampling. Once established, the geotextile is hidden within the root matrix and the area can be grazed or mown as necessary. They are not recommended for general slope stabilisation for amenity sites because they are non-degradable and do not ‘drape’ well over uneven ground. However, Pathcraft Ltd. have successfully used polypropylene ‘Netlon’ on sites in Scotland, and have found its durability necessary for mountain conditions. Its black colour makes it virtually invisible, even when viewed close by. Pieces are cut to manageable size for transport and ‘drapability’, and then pegged in position for several seasons. If done with care, the net can be lifted for reuse without damaging the restored vegetation.

Three-dimensional geotextile matting is available in a variety of materials including jute and coir. They are also available pre-seeded, with the client’s choice of seed mix, and then are simply unrolled down the slope and pegged. Brands include Greenfix (Phi Group) and GrassMat (Hy-Tex Ltd.).

Three-dimensional polypropylene matting such as Enkamat or Tensar Mat (Netlon) is a more durable product designed to be laid on a slope and then backfilled with soil and seed, to provide surface and sub-surface reinforcement. It is available in various specifications, including pre-seeded or with growing turf, and may have uses in particular locations where its durability is useful.

The general verdict amongst recreation managers seems to be that jute and coir geotextiles have uses for particular small, steep areas that are difficult to revegetate, and where trampling can be excluded. On steep slopes, over 25degrees, they appear to be more effective than hydroseeding (see below), but are more expensive. Partly due to cost, no large areas on recreation sites have yet been treated with geotextile, although upland pipeline routes have been restored using jute geotextiles. There is also the strong preference amongst managers of upland areas, where such eroded areas exist, against the use of ‘synthetic’ solutions. Geotextiles can only succeed if the other factors of trampling, grazing and drainage are also dealt with. Some open weave textiles have been found to discourage grazing, as sheep are wary of getting their feet entangled. Children, on the other hand, may see it as a novel slide or a net to climb up. All geotextiles tend to attract small mammal populations beneath them, where the animals flourish in the sheltered micro-climate and protection from predators, to the detriment of vegetation establishment!

Soil stabilisers

These are a range of products, also known as ‘tackifiers’ or surface glues, which are sprayed onto the ground to hold seed, fertiliser and substrate in place during the establishment phase. Soil stabilisers can be of bitumen, latex, or resin. They can be applied by specialist hydraulic seeding (hydroseeding) equipment, by tractor-mounted sprayers or hand sprayers.

From a large number of products on the market, those tested for upland sites were all found to perform adequately on a trial basis. Choice is likely to be determined by cost, and ease of mixing, powders being easier to apply on small areas than emulsions (Bayfield and Aitken, 1992). Hydroseeding was carried out on a trial basis by a specialist contractor on various sites in the Yorkshire Dales, with varying degrees of success (Yorkshire Dales National Park, 1993). Hydroseeding involves the application of a ‘slurry’ containing seed, fertiliser, moisture retainer and soil stabiliser, sprayed at high pressure from a lorry-mounted sprayer. The high pressure spray has the advantage that it reaches over some distance, thus minimising ground disturbance, but the disadvantage on slopes that the force of the spray can cause run-off.

More recently a sloping area of about one hectare on Pen- y-Ghent was seeded and stabilised using hand-held equipment. Apath was first delineated through the eroded area by using simple rope edging. Larger stones were moved to the side to make a comfortable walking surface, and the area was left for a week to settle. NPK fertiliser (10.15.10) was spread, followed a week later by the seed mixture, and the area was sprayed by hand using an 8% mixture of stabiliser M166 (Houghton Vaughan) diluted in water. The usual recommendation of 4% was found insufficiently sticky, the material washing down as it was sprayed. The problem with spraying slopes is to get sufficient product onto the slope to stabilise it, but without run-off. In this project the stabiliser was carefully applied in two thin coats up to the recommended rate of 3 litres/m2. An area of 10 x 20m was treated at a time, to allow the first coat to dry before the second coat was applied.

The problem of supplying sufficient water for the job was solved by lining existing small hollows with waterproof building membrane, to trap rainwater and stream seepage. This was done several weeks in advance of the spraying operation, with the pits fenced against livestock. The pits were pumped out using a small petrol pump, and mixing was done in large plastic tanks, hired from a building hire centre. The spraying operation took three people about five days.

All soil stabilisers tend to block spraying equipment, and large-hole sprayers are needed, with frequent washing out to keep them working properly. For this project, flattened water pipe was used, attached to alkathene pipe. As with all chemicals or hazardous substances, manufacturer ’s instructions must be followed, and care taken with wearing of protective clothing, disposal of containers and other procedures.

Unfortunately, a few weeks after completion of the project, exceptionally heavy rain caused large areas of the newly germinated sward to wash down the slope. However, it was felt that the technique was basically sound and would be used again on a similar site, with hopefully better weather.

Depending on dilution rates, a reasonable guide price for soil stabilisers is about 65p per square metre, which is comparable with the cost of jute geotextile (1995 price). For sloping sites, a choice between geotextiles and soilstabilisers is likely to be made taking into account factors of labour, costs of other equipment needed, water supply to the site, aesthetic considerations and personal choice.

Requirements of seed mix

The choice of seed mix will depend on the physical nature of the site, and the use to which it will be put after restoration. The mixture is determined by the percentage of different species and strains. On the same site, trample- resistant mixes can be used for path surfaces, and other mixes for non-trampled areas. In practice, on many sites there is much to be said for using a standard amenity mix (see below), suitable for the general habitat, which is readily available for staff to use as necessary on eroded patches, and for restoration as soon as other path work is completed. Where possible, this ‘stitch in time’ approach is more likely to be successful than large-scale reseeding, and to result in a natural mosaic of vegetation. Specialist advice will be needed for large areas, and on which a variety of mixes and treatments may be advisable to create a natural-looking pattern of vegetation. Any revegetation work on Sites of Special Scientific Interest can only be done after consultation with the relevant statutory nature conservation agency.

Acultivar is a named strain of a species, which is maintained in cultivation. It may be very different from other cultivars of the same species. Specialist seed advisers or seed suppliers will advise whether particular cultivars are suitable for particular locations and uses. Cultivars are distinguished by a name or letter and number after the species name.

Seeds from native British grasses tend to be much more expensive than foreign cultivars, and for this reason the latter are used on some amenity sites.

The following characteristics should be considered when selecting a mix for seeding.

Nurse species

The mix should include a species which grows rapidly to protect the soil and other seed from being washed away, and provides a suitable micro-climates for the germination and growth of other species. This is usually perennial rye grass (Lolium perenne) which establishes quickly, especially if fertiliser is applied, but declines as fertility decreases. It can be used in both acid and alkaline situations, and cultivars are available which germinate at low temperatures and are thus suitable for high altitudes. On many amenity sites, especially in upland situations, it will not persist without management intervention, and can thus be allowed to decline as local species take over.

The speed with which other species take over depends on many factors, including the vigour of the nurse crop, the natural spread of seed from nearby, and the speed of establishment of these local species.The exclusion of grazing is an important factor in allowing existing native plants to flower and set seed into adjacent newly sown areas.

Resistance to trampling

It is unlikely that re-seeded areas will be kept entirely free of trampling, whether by animals or humans. Some trampling will be desirable if the aim is to maintain a grass sward and prevent it being invaded by scrub. Species resistant to trampling may therefore be selected, and will include those with tough leaves, often in a rosette, a growing point well below the soil surface, and an ability to propagate by stems as well as by seed.

Footpaths tend to develop this type of species composition, as non resistant species are destroyed by trampling and resistant ones take their place. These differences can be seen quite clearly where path vegetation shows as a different colour, or resistant species such daisy (Bellis perennis) are in flower along the line of a path.

Level of productivity

The mix should be productive enough to give a cover that will prevent soil erosion, but not so thick that local species are unable to recolonise. Very productive strains of agricultural and sports turf grasses should normally be avoided. Fertilising the ground can also slow the return of native species because their growth rates cannot usually compete with those of sown species while soil fertility is high. Fertiliser treatment is usually needed for initial establishment, and may be needed in following years until a satisfactory sward is established.

Colour

‘Improved’grassland, containing agricultural grass species, is a brighter green than unimproved semi-natural grassland. Restored areas may be visible for some years as a bright green ‘scar ’ if certain strains are used.

Procedure

Chemical treatments

If a large area is to be treated which may involve substantial expenditure on seed, it is essential to have the soil analysed so that any requirement for lime or fertiliser can be calculated. The local office of the Ministry of Agriculture, Fisheries and Food can arrange for soil tests to be done, and will often give advice on suitable seed mixes. In Scotland, contact the Department of Agriculture and Fisheries, or one of the agricultural colleges, or in Wales, the Welsh Office Agricultural Department.

Many eroded slopes have no soil left, and in the absence of available topsoil, seeding must be done direct onto a loose stony substrate. Analysis of these substrates is likely to be meaningless as nutrient levels are so low, although the pH can be checked to find out if liming is necessary. With the addition of fertiliser, successful seeding is possible even on very stony substrates with no soil. To prevent ‘burning’ of seed, any fertiliser application should be done in advance of seeding.

Although each site should be tested for nutrient availability to establish fertiliser requirement, this may not be practical for many small areas that need reseeding. A slow-release fertiliser such as Vitax Q4 (NPK: 5.3:7.5:10) is suitable and widely available.

In areas of erosion and low fertility, fertiliser applications may be have to be repeated over several years. The initial application would be of a quick release fertiliser applied at a high rate, followed by reducing rates of slow release fertiliser for up to five years.

Timing

The optimum time for sowing seed mixes varies with the locality. In general, in the south and southwest, seed can be sown from March to May, and September to November. Slightly shorter periods of April and May, or August and September are possible in the midlands and parts of the north. In the drier eastern regions, spring sowing is more risky due to summer droughts. In the upland areas of the north west and Scotland, spring sowing is more reliable than autumn sowing, which may fail in cold and wet seasons. Within this general pattern there is much room for variation according to weather patterns and particular localities.

Methods of sowing

For small areas, simple broadcast sowing by hand from a bucket or bag is the best method. For larger areas, a seed fiddle can be used. It is preferable, but often not possible in the uplands, to sow on a dry, still day. If it is windy, walk up and down in the direction of the wind, so that any blown seed falls in the required area.

For mechanical sowing, seed drilling by tractor and drill directly into the ground is not usually possible because of ground conditions. Seeding from a spreader may be possible but often windy conditions cause problems. The ideal for many upland areas would be low-level seeding attachments for quads or All Terrain Vehicles, which are being developed.

Tilth

On flat ground or gentle slopes, preparing a seed bed is is worthwhile even where the site looks beyond redemption. Soils on trampled areas will be very compacted, and should be broken up with a fork or pick. Ideally this should then be left to be broken further by weathering, but normally this will have to be done straightaway, by knocking the lumps apart with the fork or rake. Rake to produce as fine a tilth as possible. Any remaining soil on slopes should be raked to break the surface crust, but do not loosen more than this, or you may encourage further erosion.

Topsoil brought from elsewhere should be roughly spread with a rake, and then trodden to firm it. Rake the surface again to produce the final tilth. Slopes should be raked from the bottom upwards. If any mulch such as sewage sludge or composted bark is being used on stony slopes, it must be well raked in so that the mulch and substrate are mixed to at least 100mm. Otherwise the plants will merely root into the surface mulch, which will slide away like a carpet after heavy rain or snow.

Eroding stony slopes may be too unstable for any raking or other preparation, and seeding may have to be done in stages over several years. The method used by the National Trust Carneddau Footpath Team is as follows. The area is first fertilised with Vitax Q4 at the rate of a golf ball-size handful per square metre. About a week later, an upland amenity mix (see below) is sown, at the rate of one tennis- ball size handful per square metre. This is normally done in May. Later that year, or the following spring, the area is picked over to remove large stones. This cannot be done initially before any seedling establishment, as the slope is too vulnerable to erosion. Bare patches where stones were removed are seeded, and any failed patches are reseeded. Eroding material covering newly-established grass is also carefully removed so that it doesn’t smother growth. This is repeated again as necessary until the slope has stabilised.

Seed mixes

For special sites and large areas, seed mixes are likely to be chosen with expert advice from the statutory nature conservation agency, wildlife trusts or specialist seed advisers. However, for many amenity sites, the important properties for a seed mix are that it establishes quickly, is moderately productive and trample resistant, reasonably priced and commercially available in sufficient quantity. Many seed mixes for such sites are based on a mixture of perennial rye grass (Lolium perenne), smooth meadow grass (Poa pratensis), common bent (Agrostis tenuis) and fescues (Festuca sp.). Of the fescues, sheep, red and Chewing’s may be used. All the above species are available in various cultivars, on which seed suppliers will give advice.

Seeding rates will vary with the situation, but for most purposes a rate of between 5 and 15g/m2 (50-150kg/ha) will be sufficient.

Three typical amenity mixes are given below. The first is used in restoring the Pennine Way in the Peak District.

The following mix is used by the National Trust on amenity sites in the Lake District, North Wales and elsewhere.

The following mix is used by Pathcraft Ltd. on upland sites in Scotland.

The seed mix is spread at 30g/m2, together with a mini granular slow release fertiliser (NPK 1:1:1) at 30g/m2.

The following examples are from various amenity sites which have been successfully restored, and are given here as examples of particular seed mixes for various situations.

Coastal cliffs

This mix was successfully used at Kynance Cove on the Lizard Peninsular (O’Connor, Goldsmith and Macrae  1979), to restore an eroded area of cliff top. Local topsoil was brought in and trampling was excluded by the construction of a new path. Locally collected seed was used in addition to the commercial seed listed above, and germinated slightly better than the commercial seed. The percentages quoted above are merely a record of what was used in this case, and are not necessarily significant. Different proportions plus additional suitable species could be used according to availability.

Saline areas lower down the cliff did not establish successfully. This very extreme type of location would require seeds collected from the immediate area to ensure they were suitable maritime ecotypes, and the complete exclusion of trampling.

Calcareous soils

The following is an example of a seed mix for chalk downland.

Calcareous subsoil

The seed mix given below has been used for the reinstatement of vegetation on raw calcareous subsoil, thus obviating the need for topsoil. The absence of perennial rye grass from the mix slows the initial establishment of the sward, but allows the quicker invasion of local species.

The mix should be sufficient to prevent erosion, and has a pleasant grey green appearance. Fertiliser is not necessary. The recommended seeding rate is 12.5g/m2.

Acidic peat

This seed mix was used at Risley Moss, Warrington, to establish grass in clearings in acidic woodland. The pH was raised to 5.5 by liming at 0.8kg/m2. This should be done immediately before seeding as lime is rapidly leached from the soil. Phosphate levels were also low, so ‘Basic Gafsa’ (P2O5 content 29%) was used at 10g/m2. This is not lost by leaching and is best applied several weeks before sowing. A general fertiliser (NPK 15:15:15) was also used at 38g/m2. Trampling was excluded for at least a year after seeding (JD Moffat; unpublished paper).

The mix below was used on heavily trampled peat at Beacon Fell, Lancashire. Tests showed that trampling further lowered the pH as well as causing compaction and the formation of anaerobic conditions, so giving no chance of natural recovery even if trampling was excluded.

After drainage of waterlogged areas, limestone was applied at 2kg/m2, and Rotovated into the peat. Fertiliser (NPK 17:17:17) was then applied at 75g/m2, followed by grass seed at 20g/m2. The seed bed was then rolled.

Trampling should be excluded for at least four months, and the grass cut and rolled as necessary to encourage the development of a resistant sward.

Mountains

Extremes of climate, steep slopes, thin soils and a short growing season reduce the number of species able to survive on mountains, and slow the rates of growth and seed production. Natural recovery of damaged ground occurs only very slowly.

Establishment of trample-resistant turf on paths is unlikely to be possible, and efforts at revegetation should be directed to damaged areas where trampling can be reduced or excluded. The aim of seeding is to prevent further erosion and provide a micro-climate which encourages invasion by local species. Up to about 500m, a wide range of annual and perennial species should invade. Heather (Calluna vulgaris) has been found to invade sites up to 800m in the Cairngorms, in the absence of trampling.Above this height, recolonisation is slower and is dominated by mosses. Seeding has been successfully done to an altitude of 1100m in the Cairngorms.

The following seed mix can be used on sites up to 800m, at a minimum rate of 9g/m2. This should be increased to 15g/m2 on steep slopes or sites without topsoil.

Small amounts of the following species can be added to the mix, for use at altitudes of up to about 500m.