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Planning a garden with slopes will surely be a challenge, but changes of level certainly give any garden added interest, and add an extra aspect to sloping landform design. Sloping garden designs will need to be very carefully thought about at the  planning a garden stage.

Designing a garden on sloping landform will depend on:

1. The severity of the slope (degree of slope or steepness of slope) 2. The size of the garden

3. Features to be included

Factors to be considered while planning a landscape on slope (Anderson) :

4.1.1. Drainage

If water drains to the down of the slope, water channel clues and channels are narrow, then the erosion control will be a problem and slope may be more unstable than required. This is something to keep in mind when landscaping is done  –   slope stability. To check this, a hole is dug and filled with water and time taken by water to drain is noted. If drainage occurs within an hour or so, slope is relatively stable. If it takes several days to drain, then slope is highly unstable. Water accumulation on the slope is controlled because wet soil and mud on a steep hill can cause erosion and slide issues.

4.1.2. Soil

Proper analysis of type of soil and is water holding capacity should be done. It will decide the type of planting material that will best grow here and better secure the slope. To check the type of soil, a hole should be dug somewhere on the slope,  preferably where landscaping is to be done and result is noted down. If soils on top

slides down the slope easier, then the soil is rocky or clayey. (Anderson)

4.1.3. Access and maintenance

Access to gardens on slope is necessary for maintenance, weeding, pruning and watering, and can take different forms. If a very small garden, access can be made from the edges. Larger gardens require access via paths, walkways or steps. Steps and  paths down the slope can be used to more appropriately access the terraced gardens.

(Anderson)

4.1.4. Rainwater and runoff management

Rainwater and runoff management is interrelated with irrigation, plant selection and erosion control. Rainwater can prove harmful for a hillside garden. If unchecked, it can cause serious erosion. Rain running down the hill and off the landscaped area into the residential spaces is a problem. Rain can become an asset with proper design.

Terraces accomplish this inherently by providing level garden areas for the rain to soak in and not runoff. Where a slope is not terraced, berms across the hillside with narrow swales behind, and winding stone-lined creek beds can slow the movement of water, allowing it to soak in. Garden at the bottom of the slope allows the last of the runoff to gather and irrigate plants assembled there.

If there is a slope uphill from the residence, berms can also be used there to send surface water around the house for use in lower gardens.

Aesthetically pleasing ground cover is also an easy solution to control water runoff. If the slope is not too steep, a ground cover creates a clean appearance that is easy to maintain. Ground covers such as Blue Rug Juniper, Baltic English Ivy and buffalo grass are low maintenance and well suited to sloped areas. There are also flowering ground covers for inclines like Creeping Phlox, Vinca Minor vines and Sweet

Boulders or rocks should be strategically placed around the plants to slow down any water runoff. Stones offer a natural appearance, but they also trap the earth and moisture within it.

4.1.5. Irrigation

Since hand watering of a landscaped area on slopes is not very convenient, there is a need to install drip irrigation. Alternatively, on a low-water slope landscape, drought tolerant plants can be selected; hand watering them first two summers can be done, rather than installing irrigation.

Plants put at the top of a slope will get the least water, those in the middle somewhat more, and those near the bottom the most, as water running downhill section is soaking in more and more. Accordingly; top, middle and bottom regions are planned.

The most drought tolerant should go toward the top, and those that can tolerate more water closer to the bottom. Exposure plays a factor too. And the direction the slope faces will impact plant selection; southern and western exposures are hotter, and northern and eastern can take plants that can stand less direct sun. (Anderson)

In addition to normal gardening issues mentioned above, particular challenges hillside gardening must also be considered while planning a landscape on sloping site:

1. Erosion control and retaining the hillside 2. Rainwater and Runoff

3. Structural safety for landscape design

4. Plant selection and location — for erosion control and relating to water needs and exposure

5. Zoning and water behavior on slopes

6. Accessibility to the beds or plantings for maintenance and moving 7. Steepness of paths and steps, and safety aspects

Design considerations for gardens sloping up away from the house (or sloping down towards the house)

A garden that slopes up from the home is one that can be seen to an even greater degree than a flat site. It becomes a garden that can be terraced so as to bring aesthetical values to the residence.

1. Patio on a higher part of the garden, away from the house may look interesting. Raised wooden decks can be attractive and they can be constructed in such a way as to allow light to filter down to the windows of lower storeys.

2. The rest of the garden could be a series of attractive terraces probably with steps.

3. Professional advice on structure should be taken and as to avoid water running down the slope and collecting near the house. (Sloping Garden Design Ideas, 2014)

Design considerations for gardens sloping down away from the house (or sloping up towards the house)

1. High level decking may look interesting.

2. The rest of the garden could be terraced with steps, and attractive planting and groundcover to make space look aesthetically pleasing.

3. Advantage of great views. (Sloping Garden Design Ideas, 2014) 4.2. Landscaping principles on sloping sites

Hillside landscaping is the most challenging of all residential design problems.

Whether it is a natural undisturbed slope or one composed of cut-and-fill, there are five essential principles that should be taken care of while designing on slopes.

(Gilmer)

1. Views should be preserved while solving problems.

Residence built within forested hillsides often cleared to increase the view. The trees have vast roots that have held the soil in place for a long time, and when trees are cut down the roots die and the soil becomes vulnerable. For this reason it is far better to keep trees living whenever possible.

All the new trees, shrubs and structures proposed between the house and top of slope should be taken care of. If trees are too large these can interfere with the view.

Trees planted on the slope itself can over time exceed the height of the slope to encroach into the view. This is more important where a terrace may be graded into the slope further down where trees are planted for shade. Trees with a low spreading

canopy should be planted rather than an upright conical form such as a fir tree to canopy should be planted rather than an upright conical form such as a fir tree to avoid repeated

avoid repeated topping in topping in the future. the future. (Gilmer)(Gilmer) 2.

2. Slopes should be taken up gradually as Slopes should be taken up gradually as possible.possible.

A very gentle slope is not much different than a ‘flats’ garden, but a steeper slope A very gentle slope is not much different than a ‘flats’ garden, but a steeper slope certainly is.

certainly is.

Any time a slope is cut its integrity is compromised, therefore its more better if less Any time a slope is cut its integrity is compromised, therefore its more better if less slope is cut. Cutting into a slope removes topsoil to expose subsoil, often heavy clays slope is cut. Cutting into a slope removes topsoil to expose subsoil, often heavy clays or shale that are poorly drained or lack microbial action of a living topsoil. This is or shale that are poorly drained or lack microbial action of a living topsoil. This is why the planting on so many cut slopes and home pads on exposed subsoil are prone why the planting on so many cut slopes and home pads on exposed subsoil are prone to failure.

to failure.

To preserve the slope, grading is done with a series of shorter terraces rather than one To preserve the slope, grading is done with a series of shorter terraces rather than one or two very large ones graded with cut and fill. The larger terraces may require or two very large ones graded with cut and fill. The larger terraces may require extreme erosion control measures on the cut slope and a substantial retaining wall extreme erosion control measures on the cut slope and a substantial retaining wall must be specially engineered to hold the fill. Such walls are constructed with footings, must be specially engineered to hold the fill. Such walls are constructed with footings, sometimes extending down to bedrock. Residences on moderate to extreme slopes are sometimes extending down to bedrock. Residences on moderate to extreme slopes are  prone to mudslides and slope failures in extreme weather.

 prone to mudslides and slope failures in extreme weather. (Gilmer)(Gilmer) 3.

3. Plants with extensive root system should be used to bind the slope deepPlants with extensive root system should be used to bind the slope deep underground.

underground.

Erosion and depth of the soil can be issues in a sloping garden, so choosing the right Erosion and depth of the soil can be issues in a sloping garden, so choosing the right  plant for the right spot is the key. Slope is composed of different soil la

 plant for the right spot is the key. Slope is composed of different soil la yers. When theyers. When the slope has been altered to create building pads, the natural binding of layers may be slope has been altered to create building pads, the natural binding of layers may be lost or compromised. When extreme weather such as heavy rains falls on these sites lost or compromised. When extreme weather such as heavy rains falls on these sites the water may travel through weaker seams to saturate layers deeper down. When the water may travel through weaker seams to saturate layers deeper down. When they become wet enough they lose their cohesive qualities and slough off in layers.

they become wet enough they lose their cohesive qualities and slough off in layers.

This is usually the cause of slope failures during rainy seasons.

This is usually the cause of slope failures during rainy seasons.

When planting is done on slope, trees are selected with a deep network of fine roots.

When planting is done on slope, trees are selected with a deep network of fine roots.

The larger the root system the better, so trees are highly effective at binding subsoil The larger the root system the better, so trees are highly effective at binding subsoil layers, with their extensive roots. There has been a great deal of study on the use of layers, with their extensive roots. There has been a great deal of study on the use of fast growing drought resistant trees such as acacia, planted on slopes. They were fast growing drought resistant trees such as acacia, planted on slopes. They were topped every year or two to force growth energy into expanding the roots for more topped every year or two to force growth energy into expanding the roots for more

 precluded

 precluded widespread widespread use, use, but but it it is is still still recommended as recommended as a a powerful powerful tool tool for for solvingsolving site

site specific specific problems. problems. (Gilmer)(Gilmer)

What to plant on a sloping landform and where on the slope to plant various species What to plant on a sloping landform and where on the slope to plant various species are key considerations. Shrubs require less maintenance than perennials, and in are key considerations. Shrubs require less maintenance than perennials, and in addition, generally have a more extensive root system. Attractive foliage or flowers addition, generally have a more extensive root system. Attractive foliage or flowers can be chosen, and mix and matched to create attractive mounds of color and texture.

can be chosen, and mix and matched to create attractive mounds of color and texture.

Plants like geraniums and begonias can be planted to protect slopes from being Plants like geraniums and begonias can be planted to protect slopes from being washed away by rain. Good plants for a slope also include California lilac, Creeping washed away by rain. Good plants for a slope also include California lilac, Creeping  juniper,

 juniper, Purple Purple coneflower, coneflower, Rattlesnake Rattlesnake master, master, Russian Russian sage, sage, Snowberry, Snowberry, StarStar  jasmine, common

 jasmine, common periwinkle, Siberian periwinkle, Siberian carpet ccarpet cypress. Add ypress. Add plants that plants that strengthen andstrengthen and  bind the soil while adorning

 bind the soil while adorning the slope. (Anderson)the slope. (Anderson)

Shrubs which can be planted on slopes include Arctostaphylos, Ceanothus, Erica, Shrubs which can be planted on slopes include Arctostaphylos, Ceanothus, Erica, Helianthemum and Euonymous. Drought tolerant plant selections include Baccharis Helianthemum and Euonymous. Drought tolerant plant selections include Baccharis  pilularis 'Twin Peaks',

 pilularis 'Twin Peaks', Cistus, Correa, Grevillea, Cistus, Correa, Grevillea, Mahonia, Rhamnus and Rosmarinus.Mahonia, Rhamnus and Rosmarinus.

Ground cover plants are a perfect solution for covering sloping areas. Using ground Ground cover plants are a perfect solution for covering sloping areas. Using ground cover plants on any slope helps retain or hold the soil on the slope. Additionally, cover plants on any slope helps retain or hold the soil on the slope. Additionally, groundcovers fill the area and crowd out weeds, making it easier to maintain. Hardy groundcovers fill the area and crowd out weeds, making it easier to maintain. Hardy  perennials and shrubs can also be included as groundcover plants like hostas, sage and  perennials and shrubs can also be included as groundcover plants like hostas, sage and snowberry. Ground cover plants such as Aubrietia are excellent for steep banks; they snowberry. Ground cover plants such as Aubrietia are excellent for steep banks; they suppress weeds, help stabilize the soil and needs low maintenance. (See

suppress weeds, help stabilize the soil and needs low maintenance. (See Figure 4.1 Figure 4.1)) Planting pockets near the large boulders should be created for seasonal color or Planting pockets near the large boulders should be created for seasonal color or creeping shrubbery like Cotoneaster or vinca. The stones can be treated with the moss creeping shrubbery like Cotoneaster or vinca. The stones can be treated with the moss and to give them a weathered and time-elapsed effect. A small stream can also be put and to give them a weathered and time-elapsed effect. A small stream can also be put in with for sound and visual effect.

in with for sound and visual effect.

While putting larger trees on slopes, certain things should be taken care of. Area While putting larger trees on slopes, certain things should be taken care of. Area where the trees are to be planted should be leveled off so the tree stands on level and where the trees are to be planted should be leveled off so the tree stands on level and not on a slope. A retaining wall can be put behind the tree to prevent dirt from not on a slope. A retaining wall can be put behind the tree to prevent dirt from washing over the roots too much. Decorative stones can also be used to turn it into a washing over the roots too much. Decorative stones can also be used to turn it into a focal point. Too many upright plants should be avoided because they block the view.

focal point. Too many upright plants should be avoided because they block the view.

Larger trees, shrubs and plants should be planted vertically, not pointing out of the Larger trees, shrubs and plants should be planted vertically, not pointing out of the

water and allow it to soak into the soil around the plant. Smaller plants and ground water and allow it to soak into the soil around the plant. Smaller plants and ground covers can be planted to fill in while

covers can be planted to fill in while larger plants take hold with the hillside.larger plants take hold with the hillside.

Composting the soil usually proves helpful

Composting the soil usually proves helpful —  — certainly if hillside soil is sandy or clay.certainly if hillside soil is sandy or clay.

Hillside gardens, like all gardens should be well mulched. But the choice of mulch is Hillside gardens, like all gardens should be well mulched. But the choice of mulch is more critical. Things like straw, small bark or cocoa hulls will wash away easily.

more critical. Things like straw, small bark or cocoa hulls will wash away easily.

Finely shredded redwood, or the coarser shredded

Finely shredded redwood, or the coarser shredded rather than chipped mulches tend torather than chipped mulches tend to knit together into a mass, and are less (but not completely) susceptible to being knit together into a mass, and are less (but not completely) susceptible to being  pushed downhill by

 pushed downhill by rain. (Anderson)rain. (Anderson)

F

Figuigure 4.1: Grre 4.1: Ground covers for steeound covers for steep slopep slopess(Alders)(Alders)

Certain points should be taken care of regarding landscaping on slopes:

Certain points should be taken care of regarding landscaping on slopes:

1.

4. Trees and shrubs which are locally native will be easier to establish than moreTrees and shrubs which are locally native will be easier to establish than more exotic species, and in keeping with the character of the area.

exotic species, and in keeping with the character of the area.

5.

5. On exposed sites, consider more substantial shelter planting of native trees toOn exposed sites, consider more substantial shelter planting of native trees to help reduce the effects of cold winds and driving rain, whilst also increasing help reduce the effects of cold winds and driving rain, whilst also increasing  privacy.

 privacy.

4. Surface soils should be protected from rain spatter and runoff.

When rain falls on the slope, each drop that falls on bare earth dislodges particles of soil. As runoff runs down slope, the velocity causes more particles to be scoured from

When rain falls on the slope, each drop that falls on bare earth dislodges particles of soil. As runoff runs down slope, the velocity causes more particles to be scoured from