Shady Gardens

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Aug 152008
 

Photo © Bulleen Art & Garden

Many established suburban gardens have large and established trees, which cast shade over part or most of the garden. Also, as housing densities increase, and many taller homes are built, being able to garden successfully in shady areas will become more relevant.

Gardening under established trees

Established trees create an environment underneath in which it is difficult to establish other plants. Not only does the root system of the tree compete for water and nutrients, but the canopy of the tree prevents most of the rain from reaching the ground directly underneath. This creates a soil environment with little nutrient in the soil and very little moisture available to other plants. However, there are several ways to successfully garden under established trees.

Under some trees, you may be able to dig the area over and remove the small roots in areas around the tree. Keep in mind that you do not want to damage the trees by removing too many of the trees fine feeding roots. Mix in organic matter to the areas that have been dug over, and plant in this area. The plants will have to be relatively tough, as they will need to compete with the tree roots that will grow through this newly dug soil quickly. Frequently mulch the planted areas with compost and manure, topped with a thick layer of mulch. You will need to water these plants frequently as the trees roots will take up most of the moisture.

Photo © Bulleen Art & Garden

Build up garden beds over the tree roots. Some species of tree will be more tolerant of this than others, so it is best to check first. These beds cannot be built up too thickly because this has the potential to damage or in some cases kill the tree. Try to limit the built up area to 15cm depth, and don’t cover the whole root system of the tree. Again, fairly tough plants will need to be chosen for this area as the tree roots will quickly grow up into this new soil. One option with this method is to fill with an open mix, such as orchid bark, and plant Bromeliads or Orchids.

Using root barriers and trenching. This method has the potential to damage trees, especially if too much of the root system is damaged. The aim is not to restrict tree root growth altogether, but to limit the growth of roots through a garden bed to allow new plants to establish. Do not sever significant roots (those with a diameter greater than 15mm). The trench should be dug to a depth of 1 metre, the root barrier installed, and the trench backfilled. The root barrier must protrude above the surface of the soil to be effective.

Plant into pots under the tree. This is the only option when digging under the tree will cause too much damage to the tree, or the tree roots are too densely matted under the tree to dig into. When growing plants in pots under trees, watering will need to be checked regularly as most rainwater will not reach the pots.

Photo © Bulleen Art & Garden

Maintenance of shady gardens

Most of the plants that grow in shady positions will grow slower than those that grow in full sun. However, fertilising and improvement of the soil and watering will need to be done on a regular basis. Also, check that plants are not being smothered by fallen leaves, bark and twigs. Remove any leaves that are smothering plants quickly, and compost these to return to the soil under the trees.

The canopy of some trees may become so dense that the light levels are too low under the trees to successfully grow other plants. The canopy of many trees may be selectively thinned to allow more light to penetrate. Start by removing all dead wood from the tree. As a general guide, no more than one third of the volume of the canopy should be removed at one time. For old, established, significant or valuable trees we strongly recommend that an arborist do any pruning work.

Ideas and plants for shady spots

Rather than simply list plants that will grow in shade, below are a few design suggestions along different themes.

A tropical theme (for Melbourne weather)

Palms: Try Archontophoenix for height, or Phoenix roebelinii (approx. 2.5m)

Cordyline stricta: Very tough. Use as a palm like plant if you don’t have the room for a palm.

Ferns: Birds Nest Ferns, Jungle Brake, and Button Ferns

Cycas revoluta: Grow this Cycad in a large feature pot. Try a bright blue or deep red, or jade green glazed pot

Nandina domestica nana: Use for year round foliage colour. A drought hardy small shrub

Summer Annuals: Try Coleus and Impatiens in hot colours

Liriope variegata: Use in the foreground for a light highlight all year

Ajuga: Try Jungle beauty or Caitlins jiant for a ground hugging cover with blue flowers

Plectranthus: Try Mona Lavender, for foliage and flower colour.

Clivea miniata: Use in the middle ground on mass. Dark strap foliage and bright orange flowers

Canna ‘Tropicanna’: Brilliantly bold striped foliage and bright orange flowers.

Sculpture: Balinese sculptures and pots mix well with this style as well as glass and steel water features

Garden under a Gum Tree

Kangaroo Paws: Plant some large ones towards the back, and shorter varieties towards the front

Indigofera australis: Tall and wispy, plant at the back of the bed

Correa: Try Dusky Bells or reflexa Dwarf

Westringia: Plant where they will get light shade. They may need pruning to keep dense

Dianella: Plant a big clump or drift of these

Plectranthus argentatus: Use in the more shady areas to show off the silver foliage

Sollya: Edna Walling Blue Bells Plant next to a rock or old piece of wood, so it can scramble over. Other varieties of Sollya can pose a weed problem

Eriostemon: Plant in the middle of the bed. A fairly solid shrub to use as a backdrop

Viola hederacea: A pretty groundcover for moister areas

Dichondra repens: Another ground hugging plant with kidney shaped leaves

Poa labillardieri: Plant clumps of this grass in dry spots that get only light shade

Scaevola: Small blue or pink flowers on a spreading groundcover

Myoporum parvifolium: Another groundcover plant, use in front of Poa

Brachyscome multifida: For colour most of the year with their dainty daisy flowers

Sculpture: Try rusty metal or dry glazed terracotta pieces and rustic style pots. Bird baths in any style

Rocks and logs: Only source these from a nursery or landscape supplies yard. Removing these from other areas is robbing animals of their homes

A woodland garden

Anemone japonica: Autumn windflowers in white or pink

Helleborus: Plant in a large drift for winter colour

Plectranthus ecklonii: Plant towards the back in a large clump or drift. Bright blue flowers in autumn

Aquilegia: Plant in light shade in little clumps

Hydrangea quercifolia: A good background shrub with attractive autumn foliage

Digitalis (Foxgloves): Plant these in autumn is clumps at the back of the bed

Lamium maculatum: An excellent groundcover in the shadiest driest spot. The silver foliage will light up a dull corner

Muscari: Plant bulbs in autumn in drifts under deciduous trees and shrubs

Viola labradorica: Wood violets, with small purple leaves

Hosta: Many foliage colours to chose from. Plant these for summer foliage interest

Pieris: Attractive tall shrubs for the back of the bed

Autumn fern: A beautiful fern with bronze coloured new growth

Tiarella: Plant in clumps or drifts in light shade. The feathery white flowers continue through summer.

Sculpture, pots, water features and ponds

Stone sculpture would suit this style. Perfect for setting up a small pond or water feature. Both glazed and rustic style pots would suit.

A dark sideway

Pomaderris aspera

Liriope Evergreen Giant

Clivea miniata

Strelizias in pots

Bamboo in pots Cordyline stricta

Trachelospermum jasminoides:

Palms, upright types Camellia sasanqua or hybrids suitable to espalier

Alpinia zerumbet

Dianella

Hedychium gardnerianum

Clerodendrum

Hydrangea petiolaris

Yucca elephantipes

All year colour

(Not all of these plants are in flower all year round, but you can use combinations to ensure your garden always has great colour)

Daphne odorata: Winter / early spring colour

Azaleas: Winter / early spring colour

Impatiens: Spring / summmer / autumn colour

Plectranthus: Spring / summmer / autumn colour

Cyclamen Bluebells (scilla): Winter / early spring colour

Bromelliads: Year round colour (foliage)

Anemones: Autumn / winter / spring colour

Helleborus orientalis: Winter / early spring colour

Primula malacoides: Autumn / winter / spring colour

Fuchsias: Spring / summmer / autumn colour

Liriope: Late summer / autumn colour

Camellia japonica: Winter spring colour

Eupatorium megalophyllum:Spring / summer colour

Hydrangeas: Late spring / summer colour

Ajuga: Autumn / winter / spring colour

Primula obconica: Autumn / winter / spring colour

Cymbidium orchids: Autumn / winter / spring colour

Begonias: Spring / summmer / autumn colour

Acer palmatum cultivars: Autumn colour

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