How Does Your Environment Affect Your Planting? Getting to Know Soil and Aspect

Unsuitable plants and unanticipated garden issues can drain your time and money. Avoid easily-identified errors by getting to know your garden's soil, wind and drainage conditions before you break ground, or the bank.

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Understanding and Improving Soil

Garden soils range from sticky clays to free-draining sands. Clay soil is prone to waterlogging in winter and dries hard in summer. Sandy soil warms up early in spring, but is a challenge to keep moist in summer. Clays can be very productive and rich in nutrients if manure and grit are dug in, but sands are typically poor and, without adding manure or garden compost mulches, won't retain moisture or nutrients. The ideal "loam" soil contains a mix of clay and sand plus organic matter. Loams are dark and fertile because of the organic content, form a crumb-like structure when forked over, and have good moisture retention. Test your soil before designing planting areas; loams hold together in a ball when rolled, but crumble under pressure.

Testing Clay Soil
As clay content increases, you can form the soil into a ball or sausage, then a ring (Image 1).

Testing Sandy Soil
This soil crumbles under light pressure, won't form a ball, and feels gritty (Image 2).

Grit Improves Drainage
Large quantities of coarse grit worked into the top layer of soil (to fork depth) improves the drainage of heavy clay, but drains may also be necessary on waterlogged soils (Image 3).

Well-Decomposed Manure Benefits All Soils
Manure causes fine clay particles to clump together, improving soil structure and drainage. It also helps sandy soil retain water and nutrients, but use it only as a mulch (Image 4).

Testing Acidity

The soil pH is a measure of acidity and alkalinity — 7 is neutral, below 7 is acid, above 7 is alkaline. Acid soils suit rhododendrons, azalea, laurels and heathers while many Mediterranean herbs, shrubs, and alpines will grow happily in alkaline, lime-rich conditions. You can pick up clues about your soil by looking around the neighborhood to see what plants are thriving. Soil type can also vary around a garden due to local anomalies, so carry out several pH tests using an electronic meter or simple chemical testing kit.

Determining Your Soil Type
Taking samples from around the garden, use a test kit to check acidity/alkalinity (Image 1).

pH Soil Testing KitEnlarge Photo+Shrink Photo-DK - Garden Design © 2009 Dorling Kindersley Limited

Checking the Aspect

The direction your garden faces affects how much sun it receives and how exposed it is to wind. To work out your garden’s aspect, stand with your back to the house and use a compass to check the direction you are facing.

Typically, south- and west-facing plots are warm and sunny while north- and east-facing gardens are cooler and shadier. Filtering the wind on an exposed site reduces wind-chill, and limits damage to structures and plants. As altitude and distance from the sea increase, temperature and exposure can be adversely affected, whereas urban areas produce and hold heat, keeping gardens artificially warm.

Windy Sites
Exposure can restrict your choice of plants as well as your enjoyment of the garden. Provide shelter with hedging and other windbreaks (Image 1).

Frost Pockets
On sloping sites, cold air rolls down to the lowest point and pools there if its path is blocked. Less hardy plants here can suffer frost damage (Image 2).

Excerpted from Garden Design

©Dorling Kindersley Limited 2009

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