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.
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.
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
Liriope Evergreen Giant
Strelizias in pots
Bamboo in pots Cordyline stricta
Palms, upright types Camellia sasanqua or hybrids suitable to espalier
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