RHS Garden Planning Site appraisal Sometimes called site assessment, these are the criteria by which the designer evaluates a garden with a view to its best use: Siting of patios and other recreation areas Plant choice Style Orientation The orientation of a garden is its aspect, or the direction in which it is facing. This determines at which times of the day the garden is lit by the sun. Gardens that are south- or west-facing are predominantly warm and sunny. If enclosed, they may well be ‘sun-traps’. Conversely, east- and north-facing gardens are cool and shady. Light and shade The sun will be higher in the summer than the winter – so shadows will be longer in winter. Areas of the garden that may be well-lit in summer may be permanently shaded in winter. Topography Topography is the lie of the land – whether it is flat or sloping. Flat gardens are very calm and restful. They lend themselves to lawns and still pools of water that seem to draw the light downwards. A sloping garden is more dramatic. A slope can incorporate a moving water feature such as a stream, waterfall or watercourse (a series of linked pools with a cascade between each). A slope can also be terraced. Hollows in the ground may act as frost pockets – where cold air accumulates during freezing weather in winter. This will limit the range of plants that can be grown there. Local climate Assess the local climate by consulting the local weather station. As a rule, coastal gardens enjoy cooler summers and warmer winters than gardens inland. In the north, spring starts later and summers are shorter than in the south – shortening the growing season. The west of the country tends to be mild and damp, whereas the east is cooler and drier. A central ‘cool corridor’ runs down the UK. Gardens at high altitude are also cooler than gardens at or just above sea level. Microclimates Wherever a garden is situated, there may be different ‘microclimates’ within it. In the lee of a south- or west-facing wall, it will be much warmer than elsewhere in the garden. This may suggest the siting of a patio or deck for sunbathing, or provide an opportunity for growing plants that otherwise might not be reliably hardy. Soil types Assessing the soil type is critical and will guide plant choice. Plants that are adapted to particular soil types will thrive.
pH Acidity/alkalinity is measured on the pH scale, 1–14. 7 is neutral, 0–7 indicates acid, 7–14 alkaline. Most plants are indifferent to soil pH, but several have very specific requirements (see lists, below). You can test the soil using a soil-testing kit, but note that it is possible, particularly in a larger garden, for pockets of acid soil to occur on soil that is predominantly alkaline, and vice versa. You can sometimes guess the overall pH by looking at what seems to be thriving in neighbouring gardens. Note that you cannot judge the pH of a soil just by looking at it. Soil structure Possibly more important is the make-up of the soil – whether it is a friable loam, a light, sandy soil or heavy clay. Loamy soil is the ideal, containing a good balance of humus (decayed vegetable matter), silt, sand and clay. This will support the majority of plants. Sandy soils are low in nutrients – but are easy to work and quick to warm up in spring (good for early sowings of some vegetables and ornamental annuals). Clay soils are sticky, cold and heavy – on the plus side, they tend to be very fertile, as they retain water well (plant nutrients are dissolved in water). All soils can be improved by the addition of organic matter (garden compost, well-rotted farmyard manure, or bagged proprietary ‘soil improvers’). Either dig this in prior to planting or apply as a mulch around existing plants whose performance you are looking to improve. Drainage Good drainage is important for nearly all plants. You can tell if soil is badly drained by checking for moss on a lawn ‘capping’ – a green film on the soil surface You can improve drainage by digging in grit – about a bucketful per square metre – prior to planting. You can also test the drainage by digging a hole and filling with water. If this drains away quickly, there is no problem. If after half and hour there has been little movement, empty out the water, then dig deeper. Leave the hole over night, then check to see if water has appeared at the base. If it has, the site has a high water table. Either lay land drains to drain the site – or plan for a bog garden, perhaps with a series of decks between areas of planting. Choosing plants Designers need to select plants that will thrive in the conditions presented by the site. Also, the plants need to meet the client’s requirements, integrate with the landscape (in a rural garden, for instance) and integrate with each other. Avoid thorny and poisonous plants (including plants with attractive berries) if the client has small children. For a list of poisonous plants, see http://www.bbc.co.uk/dna/h2g2/A34899709 Which are the plants that need or prefer acid soil? Abies Berberidopsis Arbutus corallina
Camellia Cassiope
Desfontainea spinosa Erica Eucryphia Fagus Gaultheria Gentiana sino-ornata Kalmia
Magnolia (some) Pernettya Pieris Primula (some species) Rhododendron Stewartia
Which plants do well on alkaline soil? Acanthus spinosus Cotoneaster Acer negundo, A. Dianthus platanoides Eremurus Achillea Forsythia Alyssum Gypsophila Aubrieta paniculata, G. repens Aucuba japonica Hebe Bergenia Helenium Buxus Helleborus Carpinus betulus Juniperus Ceanothus impressus Ligustrum Cercis siliquastrum Lychnis chalcedonica Cistus Malus Clematis Matthiola Cosmos Paeonia Which plants do well in a light, sandy soil? Acanthus Echinops ritro Achillea Erica Anchusa Eschscholzia Artemisia Gypsophila Ballota Helichrysum Clarkia Impatiens Clianthus puniceus Lavandula Coreopsis Limonium Cytisus Nepeta x faassenii Dianthus Oenothera Which plants tolerate or prefer a heavy, clay soil? Amelanchier Eunymys fortunei Aristolochia Forsythia Aruncus dioicus Garrya Aucuba Gunnera Caltha Hedera Campsis Kalmia Chaenolmeles Lathyrus latifolius Citrus Lonicera Clematis Lonicera Cornus alba Lysichiton Cotoneaster Mahonia
Styrax japonica Styrax officinalis Trillium Uvularia Vaccinium Zenobia
Philadelphus Pulsatilla Pyrus Robinia Rosmarinus Saxifraga Sedum Sempervivum Sorbus aria Stachys Tagetes Taxus baccata Tilia tomentosa Verbascum Viburnum Passiflora Phlomis Rudbeckia hirta Sedum Sempervivum Tamarix Tropaeolum majus Yucca
Mimulus guttatus Passiflora Philadelphus Primula (some) Pyracantha Rheum Rodgersia Taxus Trollius Viburnum Wisteria