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Horticulture 1000
HT1081 - Landscaping - Environmental factors
User Needs Soft landscaping
3

Environmental factors

Environmental factors need to be carefully considered when designing or redesigning a site. These factors determine the type of plants that can be grown and the choice of hard landscaping materials and features.

Climate

Wind

Sheltered seating in a public park.
Sheltered seating in a public park.

It will be windy more often and at a greater speed on sites near the coast and in exposed places such as the top of a hill. Wind speed can be increased by the effects of tunnelling such as between high rise buildings in a city centre.

Plants and people may need to be sheltered from frequent and/or strong winds. For example, seating should be placed out of the wind if possible. People and plants prefer to be sheltered from southwest winds in New Zealand as they are very cold and create a wind chill.

Northwest winds on the Canterbury Plains can be strong and gusty, hot and dry, sucking all the moisture out of plants and the soil. Mulches can prevent soil drying out in these conditions. A pond or fountain can increase the humidity of the surrounding air to make it more pleasant for people.

Light

A vegetable garden in a sunny site.
A vegetable garden in a sunny site.

Some landscaped areas need to be in full sunlight, but others may need some shade. A children’s play area in a childcare centre or kindergarten may need shadecloth overhead during summer to protect children from harmful UV rays. Trees planted in a park or garden can provide areas of summer shade to sit under.

A flower or vegetable garden, however, needs to be in full sun. If this is not possible, garden beds should get morning sun and as much shelter from strong winds as possible.

Variegated plants need more light than plants with large dark green leaves, which can cope with some shade.

Rainfall

Hardy New Zealand plants that can cope with lower soil moisture conditions have been chosen for this street garden. They have been mulched with shredded bark.
Hardy New Zealand plants that can cope with lower soil moisture conditions have been chosen for this street garden. They have been mulched with shredded bark.

In areas of low rainfall plants should be chosen that are adapted to the climate. Organic mulches can be used under plants. These improve soil water-holding capacity and slow down evaporation of water from the soil surface. Irrigation can be put in place but it does cost money and if a lot of water is removed for irrigation it can reduce underground water resources.

In high rainfall areas drainage systems should be put in place to remove excess water. Excess water can be stored in tanks or ponds for irrigation use in dryer times of the year.

Temperature

Rhubarb in early summer.
Rhubarb in early summer.

Plants that are suited to the temperature extremes of a site should be chosen. Subtropical plants, such as citrus fruit, are only going to do well in temperate areas if they are planted in a well-sheltered position away from wind, cold temperatures, temperature fluctuations and harsh sunlight.

Frost can limit the type of plants used in a design. Many plants are adapted to cope with frost, such as herbaceous perennials that die down to a crown in autumn and send up new shoots in early spring. Examples are asparagus, rhubarb and dahlias. Deciduous trees and bulbs are also frost-tolerant.

Physical factors

Aspect and slope

A slope that faces north is going to get all day sun, summer and winter. On this sort of site the soil temperatures warm up more quickly in the spring and hold their heat longer in the autumn. These sorts of sites are used to plant early crops in spring and also used to get a late harvest of crops planted in summer. This is why north-facing sites are useful when trying to get a succession of crops harvested. North-facing sites are also people-friendly especially from late autumn to early spring.

A site that faces south will get less sun in the winter because of the lower angle of the sun. The soil will take longer to warm up in spring and will cool down quickly in autumn.
It may be an ideal site however for crops in midsummer, as the site could have more water in the soil at this time of year than a north-facing site due to less time exposed to hot sun.
Sites in a valley can be cut off from sun in the winter due to the low angle of the sun and/or the aspect of a slope.

Soil type

A stone mulch has been used on a windy site with a sandy soil.
A stone mulch has been used on a windy site with a sandy soil.

Soils containing a high proportion of clay will hold water well but unless they also have a high proportion of organic matter they may contain less air for plant root respiration. Ponding can occur on clay soils in areas of high rainfall. Clay soils contain a good store of nutrients. These types of soils are slower to warm up in spring but hold heat longer in the autumn.

Soils containing a high proportion of sand will have very low nutrient levels. They will warm up quickly but will also cool down quickly. They have high temperature fluctuations between day and night compared to clay soils. These types of soils are very free-draining and have a low water-holding capacity (don’t hold onto water) unless they also contain high levels of organic matter.

Plants should be chosen that are adapted to the soil type they will be planted in.

Soil pH

Most plants prefer a loam with a slightly acid pH of about 6.5. A loam will contain a mixture of sand, silt and clay particles as well as organic matter.

Many plants are adapted to or prefer a particular soil type and pH so it is a good idea to know where a plant originated from to match the plant to the soil conditions. Rhododendrons for example like a well-drained acid soil with a high amount of organic matter.

Topography

Depth of topsoil on a slope
Depth of topsoil on a slope.

Cold air will drain down into lower-lying areas because cold air is heavier than warm air. The depth of topsoil is likely to be greater in lower lying areas because soil particles have been washed down to these lower levels over time.

Low-lying areas can be quite wet at certain times of the year.

    

Higher up a slope the topsoil may be thinner and may contain less water. It also may have greater soil and air temperature fluctuations between night and day. All these things will need to be considered when choosing plants for a site.

Sites that are not flat may need more hard landscaping such as steps, decks and retaining walls to make them safe and practical for the user.

Complete Activity 3A in your workbook

Key points   Key points

Environmental factors that need to be considered when landscaping a site include:

  • Climate: wind, light, microclimate, rainfall, temperature, frost
  • Physical factors: aspect, soil type, soil pH, topography.

What's next?

Go to: 4 Soft landscaping.

User Needs Soft landscaping