Revision Notes

RHS Horticulture: Garden Planning – Site Assessment Part 1


Before creating a new design for a garden, it’s important to complete a full assessment of the site, including soil type, local climate, style of property, and other elements.

Every site has its own strengths and limitations. Factors to consider include:

Climate – this will to a great extent define the plants that can be grown as well as determining other aspects of the design. Does the garden have limited rainfall, or is it subject to frequent cold winds? If your location is some way above sea level, for example, you may find that you are two or three weeks behind gardens at lower levels in the spring, and the growing season will be a little shorter.

Local conditions – where is the garden located in relation to other features, such as roads, other buildings, rivers, lakes and farms? A garden that is right beside a busy road will be noisy and a key aspect of your job as designer may be to limit the noise and create a tranquil haven. If your garden is beside a stream or river it may be prone to flooding and the design and planting plan will need to take account of this too. Similarly, if a garden slopes to face the south it is going to be much warmer than a similar size garden facing north and this will have a profound influence on the overall design and planting.

Planning restrictions – in some areas and for some properties there may be restrictions on what you can do in the garden.

Style of property – most owners prefer to work with their property rather than against it. For example, if you are designing a garden for a Victorian villa you might introduce Victorian design elements, even if the overall design is contemporary. Some owners go even further, recreating an accurate representation of a period garden, in-keeping with their home.

Soil conditions – this is something we shall be exploring in more depth later in the course. Soil type is key to the plants that will grow successfully in a garden. For example, a well-drained sandy soil warms quickly and is easy to work; this sort of soil will support many more different plant varieties than a heavy clay soil that will be slow to drain, cold and difficult to work.

Size, shape and natural layout of garden area – these features will provide the basic framework for your design and determine many of your decisions.

Local Climate and Natural Vegetation



The most successful gardens tend to be created in harmony with the local climate and natural vegetation of the area rather than working against them. Gardens that are too much at odds with local conditions tend to stand out and may seem incongruous. They can also be costly to maintain as plants may need special protection or support to survive. For instance, modern technology allows us to create a lush subtropical garden in an arid location, but it costs a great deal in terms of irrigation and plant protection. A less extreme example might be a garden located beside the sea. The soil is salty and often well-drained. In these conditions it may be more effective to design a garden full of plants that thrive in the dry, salty conditions, emphasising connections to the coast with an oceanic theme.

You may wish to develop a garden that actively attracts local wildlife. This may involve planting local species as well as developing other features that encourage wildlife – including ponds, wetland areas, log piles, and food-rich borders.

climate protection



Weather control can extend the usefulness of outdoor living areas. Evergreen trees provide year-round screening and shade. Well-placed deciduous trees can screen the area from hot summer sun, while allowing maximum winter sun for solar heat. An awning or a trellis covered with plants can protect against inclement weather.

Year-Round Interest



Year-round interest is important throughout the garden, but especially in the area around the house. Evergreen trees, shrubs, and vines, plants with colourful bark or fruit, and perennials that keep their foliage or flowers through the winter are all useful additions in this regard. Pools, stone steps, paving, walls, bird feeders and baths, and other architectural features can also provide additional year-round interest.

Existing Features of the Garden



Gardens usually work best when working with the natural conditions and features, rather than against them. As a designer it is worth spending a little time in the garden, trying to appreciate its current atmosphere and deciding what the garden already has to offer. Changing features such as slopes, banks, walls and mature trees can be costly and difficult, and will not necessarily produce any better results. Often your budget is the single most important factor in deciding how much of the existing garden you can change and how much you need to live with.

Mature trees take many years to grow, so it is particularly important to think carefully before you remove such a tree from a garden. Trees bring structure and height to the garden, as well as being an important habitat for wildlife. They can also bring character, interest and seasonal colour to a design.

However, sometimes removing an overgrown tree can open up the shady garden, flooding it with light and providing a much more appealing growing environment for a wide range of plants.

Slopes and banks offer scope for constructing terraces, retaining walls, stepped vegetable beds, a waterfall, or a rock garden, as well as providing good views out over the garden, and beyond.

Areas that suffer from poor drainage can be turned into natural wetland areas, or used to site a garden pool. These areas are often difficult and expensive to drain, so it also makes practical sense to go with the conditions, rather than trying to change them. Moisture loving plants include willows (Salix) and alders (Alnus), candelabra primulas (Primula) and Caltha. (Although willows should not be planted close to the house as they have an extensive root system – the normal recommendation is not within 10m. In some soils, particularly shrinkable clay, they have been associated with subsidence; undermining house foundations and in these soils they should not be planted within 20m of a building. The same is also true of poplars.)

If you find that areas of rubble or subsoil have been left from building work, they may be used successfully to form the basis of a scree or gravel garden, rather than spending time and effort on digging them out and replacing them with good soil. This type of ground is ideal for plants that prefer well-drained soil. An advantage of gravel or scree gardens is that they often require minimal maintenance once they are established as few weeds grow through. You can then focus your attention and time on other areas.




The contour and shape of the site will play a central role in determining the type of planting – it may, for instance, be an important factor in the microclimate. A south-facing slope is much warmer than a north-facing one, and can be planted with quite different species. If planting crops, a south-facing slope means the soil will warm more quickly in the spring, stay warmer throughout the summer, and be the last to cool in the winter. It means higher yields and larger fruit or vegetables. In a garden, a south-facing slope is the place to plant sun-loving plants and shrubs. On a steep slope the practicalities of working the site may be significant – for example, is the site too steep for a lawnmower?

If steeply sloping land is to be planted it needs to be carefully terraced, with retaining walls or structures to prevent slippage of the soil during heavy rain. Often the best solution in this sort of location is to provide permanent plant cover, either with a dense cover crop, trees or shrubs, or grass. Contour planting, which is setting the rows to follow the contour of the land, can also help with runoff problems.




In a garden, boggy waterlogged areas can be dealt with in two main ways – they can either be drained (which generally means excavation and the installation of land drains) or they can be turned into a feature and used as the site for a pond or wetland area. In a horticultural venture waterlogged areas can be more of a challenge. Even with good drainage, a previously boggy area may remain prone to problems, making it unsuitable for many horticultural crops. Again, the solution may be to find a crop that suits the conditions.

Local Climate



The local climate around the planting site is crucial. It is useful to bear in mind that these may be quite different from general conditions in the area. For instance, a garden in a well-sheltered, south-facing spot may be much warmer than a similar garden only a few metres away but facing north, and as a result can grow quite a different range of species.

Within the garden there are also microclimates – each area of the garden offers unique conditions which need to be considered both when selecting plants and when deciding on a function for that area. A spot that receives full sun for much of the day might be ideal for a patio area, but plants will need to be carefully selected as many will not tolerate direct sunlight all day. Similarly, few plants grow well in a permanently shady spot, so you would need to select species carefully.

Prevalent wind directions differ with the area, season and the time of day. Where the wind direction differs in summer and winter, plantings can be arranged to block the cold winter winds from a patio and direct summer breezes into this same area. While conducting the site survey note down existing windbreaks provided by plants and structures already on the site or on adjacent properties.

As well as carrying out a site assessment, as already discussed, the garden designer may want to carry out a number of further investigations. These are particularly important when working on a period garden.

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