A turfed area with minor undulations can be attractive and quite acceptable but grading may be needed to correct major irregularities. When grading, the top-soil is removed, levelling is carried out on the sub-soil, then the top-soil is returned. Few people take the trouble to level a site properly with spirit level, straight edge and pegs, but for fine ornamental lawns, particularly small areas with formal surrounding features, and games areas, it is worth the effort involved. DRAINAGE Thorough digging and breaking up of the sub-soil where this is compacted, a problem often encountered on recently vacated building sites, should ensure that excess moisture is not retained at the surface. If, however, the site is known to be wet, level it first and then install clay or plastic drains-a single diagonal line across a wet patch, a herringbone system where the whole site is very wet. The next step is to dig the site, adding well-rotted stable manure, garden compost, leafmould or moist granulated peat at up to 141b per square yard (6.3kg per m2). On heavier soils coarse, gritty, lime-free materials can also be incorporated to improve drainage and aeration. Few lawn sites need lime. The ideal pH level for most lawn grasses is between 5.5 and 6.0, a moderately acid reaction. They can grow outside these levels but with increasing acidity or alkalinity growth problems occur. Heathland sites may be too acidic for lawn grasses. Test, and if the reading is below pH 5.0 apply a moderate dressing of lime (see Chapter 34, Manures and Fertilisers, p.297). On strongly alkaline soils the incorporation of acidic peat will help the early growth of young grasses, but will not appreciably reduce soil alkalinity. If lime is needed apply after digging, as a surface dressing. The final preparation of the site is done when the soil is fairly dry and a few weeks before sowing or turfing. Break down the clods using a seeded turf and the work of turf laying is done in the autumn or winter when there are few other pressing tasks. Turfing is, however, more i expensive than seeding. Laying to a good standard is more difficult and time-consuming than the sowing of seeds and good quality turf is often difficult to acquire. A lawn from seed is more dependent on good weather conditions for successful establishment; it takes longer to establish, and there is more risk of weed problems and disturbance by cats, birds and moles. The gardener can, however, choose a mixture of seeds to suit his needs with confidence in the eventual quality of the turf. A LAWN FROM SEED The two most suitable periods for sowing grass seeds are early autumn and spring. In early September (late August in colder parts of the United Kingdom) the soil is usually still warm but moister autumn weather has replaced dry summer conditions. Under these conditions germination is rapid (seven to 10 days). Sowing later may result in poor germination and seedling establishment with risk of substantial winter-kill in a severe winter.