Sowing

General considerations

1. Sowing can be used to establish a vegetative cover in areas where transplanting is impractical, eg where there is very little blown sand, where there is insufficient transplant material or where a large area must be treated quickly.
2. Dunes are poor in several important nutrients, so fertiliser applications are usually required at the time of sowing and often afterwards also. Mulching. thatching or binding also aids seedling establishment.
   Nature reserves and other sites of scientific interest should be sown with native dune species only and fertilisation should be kept to the minimum.
3. Do not sow exposed windward faces of foredunes unless these can be stabilised with binders or bv other methods. Seeds of dune-building grasses take at least six months to germinate and are easily blown away by high winds during this period. Other seeds germinate more quickly but seedlings are unlikely to survive in unstable soils. Sowing is also likely to fail where there is significant sand drift or flooding with salt water.

Dune grasses

Native dune-building grasses have a poor rate of seedling regeneration in the wild. Marram, for instance, has a maximum germination capacity of only about 15% (Pizzey, 1975, p287). Attempts to sow them have met with only limited success, although further experimentation may improve techniques.

Adriani and Terwindt (1974) give further information on harvesting, processing and pre-treating seeds to improve germination and facilitate mechanical sowing. These are suitable, on the whole, only for very large planting schemes or they do not produce significantly better results than simple hand sowing. In the present ‘state of the art’, it seems best only to sow dune grasses to supplement transplanting and to use simple hand methods to harvest and broadcast seeds even though coverage may be uneven and results sporadic.

Commercial supplies of marram grass are limited, but according to availability, may be obtainable from W W Johnson and Sons Ltd, London Road, Boston, Lincolnshire, or British Seed Houses Ltd, Bewsey Industrial Estate, Pitt Street, Warrington WA5 5LE. Any supplies will be listed in their seed catalogues, available annually. In 1986, W W Johnson were able to supply marram seed at £6 per 100g. There should be about 300 seeds per gram, to be sown at the rate of 100 seeds per square metre. All marram seed is from native stock.

Harvesting and storing seeds

1. Harvest seeds of sand couchgrass, sea lyme grass and marram between mid July and mid August. Test that the seed is mature by picking a handful of flower spikes and beating them across the hand. Sand couchgrass seeds cling to the spikes but the spikes become brittle when ripe and should break into pieces. With the other two grasses, some seeds should fall out of the beaten flower spikes. Don’t wait too long after the seeds ripen to harvest them or they will be dispersed by the wind or eaten by mice and voles.
2. Cut off flower spikes with a knife and collect them in baskets or sacks. Allow them to dry in a well ventilated room. Crumble or chop the spikes fairly finely, since if you sow large pieces they may be blown away by the wind (but see point c under ‘Sowing’, below).
3. Sea lyme grass seeds can be stored air dry at room temperature (68°F, 20°C) for a year and probably longer without losing viability. Marram seeds actually improve in viability with a year’s storage. Seaton (1968) reports good germination of sand couchgrass after one year, so it is likely that this species also benefits from storage.

Sowing

1. Sowing may be done in autumn or spring, but in either case, you should sow as early in the season as possible to allow seedlings to become established before winter frosts or summer drought. Ideally, sowing rates should be based on germination tests. In the absence of these, assume 10% fertility or less and sow to get 100 fertile seeds per square metre. If you sow too densely, many seedlings will die from overcrowding.
2. If the ground is hard, hoe or rake it before sowing. Where possible, roll it to compact it (eg by Land Rover) and then rake it, seed it and roll it again. Obviously this cannot be done on soft slopes, in which case a binder is especially useful. On bare sand, the use of a mulch, with or without binder, is essential to keep the seeds from drying out and to promote adequate germination.
   Two suitable mulches are seaweed, and where locally available, bog peat. The peat should be spread in a layer of about 20mm (3/4″), and then the seed sown and raked into the sand/peat surface. If using seaweed, first rake the seed into the sand, to avoid direct contact with the seaweed. Then spread a 50mm (2″) layer of wet, ‘fresh’ seaweed, which will dry out to a layer about 10mm (0.5″) thick.
   For large-scale programmes you can combine mulch, seeds and binder and spray the mixture over the surface using a mechanical crop sprayer (Countryside Commission for Scotland, 1977, 1978). If a mulch is not used, apply a fertiliser either as a base dressing (raked into the topsoil before seeding) or as a top dressing after the grass has become established.
3. Another method. which has worked well with marram at Scolt Head Island. Norfolk, is to ‘plant’ whole flower spikes in late summer and autumn. Cut spikes off the seeding marram in an area of vigorous growth and put them into sacks for transport. Stick the seed heads into the sand at about 3m (10′) intervals or, if the seed is easily shed, broadcast it directly.

Other grasses and herbaceous plants

Mixtures of meadow and other grasses and herbaceous species have been used with success to seed bare backdune areas which are not normally prone to wind erosion. They have also been used to stabilise eroded machair surfaces and, at Camber, East Sussex, to treat accreting dunes – sites where agricultural and amenity factors justify the widespread use of mixed non-dunespecies.

Seed mixes may be ‘off-the-shelf’ sports turf mixes or they may be specially formulated for dune use, with drought- and winter-resistant cultivars. Each site differs, so it is best to seed experimental trial plots first before going ahead with a large-scale programme.

The Countryside Commission for Scotland (CCS, 1980) recommend a basic seed mix of 60% slender creeping red fescue, 30% perennial ryegrass, 5% smooth-stalked meadow grass, and 5% white clover. The slender creeping red fescue group of cultivars are salt tolerant, spread by running roots, and can be heavily grazed or trampled. Two especially salt-resistant cultivars are ‘Dawson’ and ‘Oasis’. The ryegrass gives a rapid initial cover, dying out as the drought resistant and slower-growing fescue takes over. The white clover is important as it fixes nitrogen from the air, so increasing the soil fertility. For further details, see the Countryside Commission for Scotland leaflet ‘Reseeding of dunegrass pastures’.

Commercial mixes may include small proportions of common bent (Agrostis tenuis), smooth-stalked meadowgrass (Poa pratensis), broom (Sarothamnus scoparius) and white clover (Trifolium repens), but in general the simplest mix is best so long as it provides surface stabilisation. This allows other dune species to invade and diversify the sown area more quickly. On nature reserves it may be important to use only species native to the site. Where you are sowing the seaward side of dunes, it may be worth adding marram seed to the mix at the rate of about 25% marram to 75% mix.

For simple seeding direct onto sand, the Countryside Commission for Scotland recommend raking the seed of grass species about 35mm (1.5″) deep, to avoid desiccation. Small seeds such as clover should not be sown deeper than 10mm (0.5″). In practice it is impossible to be this accurate, and it is best to use a higher than normal seeding rate, and accept some losses. Sow at 30g/sq m, and apply a binder (see p84) to the surface to stop wind blow. With a mulch of peat or seaweed, used as described above, the rate can be lowered to 25g/sq m.

Otherwise, sow at the rate recommended by the manufacturer or, if using your own mix, establish the optimum sowing rate experimentally on trial plots. Fertilising should be delayed until after germination, as fertiliser salts can inhibit germination and young growth.

Ritchie (1975, p2576) reports that mixed grasses may be mown about a year after seeding so that they tiller and produce a denser cover. Other aftercare may include periodic fertilising, but this must be decided on a site-to-site basis and should normallv be avoided where you want the turf to develop along relatively natural lines. At machair edge restoration sites, it is important to turf as well as seed, since seeded areas tend to remain sparse until colonised by plants which spread from the turfs (Countryside Commission for Scotland, 1978, p11).