Light levels limit plant growth. It is the energy that drives photosynthesis. Shade varies in intensity, encompassing dappled light through to deep darkness. The lightest shade is offered by the vertical leaves of the gum tree, the densest by the looming condominium. Shade also changes through the day. The most challenging spot is the dark shade that suddenly gets hit by the afternoon sun; shade lovers fry and sun plants sulk. Shade is also seasonal under deciduous trees. This seasonal shade is the perfect position for woodland plants such as hellebores, their leaves being protected from sunburn throughout the summer and getting light through winter and spring to spur on flowers and new growth. Thanks to the diversity of habitats plants evolved to, there is a plant adapted to all these situations. The trick is learning to love the plants that suit, and not persisting with ones that will never work.
There is more to the shade garden than light limitation. A shade tree means root competition — the dreaded dry shade.
There are a few strategies to deal with roots that deplete the soil of water and nutrients:
Plant selection
In the driest, darkest shade, plant clivias, New Zealand Rock Lily or acanthus. If these don’t grow, little else will.
Cultivation
This approach needs to be limited and I would not cut any major roots that would harm the tree.
Fertilising
Give the shade garden extra care by regular liquid fertilising. This helps ensure the nutrients are not all being sucked up the trees.
Planting in Pots
This is an effective way to maintain special plants in the shade. No root competition and, as far as light goes, they can always be taken on holiday into the sunshine.
Shade often means shelter. This can be a good thing; frost seldom penetrates deep canopy so you can often grow plants from a slightly warmer clime — the perfect spot for a bit of subtropics down south. It also means poor air flow, creating a breeding ground for mildew and sap-sucking insects. The scale, aphids and whitefly that attack house plants equally thrive in the shade.
In the shade garden, foliage beats flowers every time. Many old shady gardens, such as the botanic gardens of our capital cities, are symphonies of green.
Instead of asking, “Where are all the flowers?” revel in the use of bold foliage plants such as monstera, gunnera, hosta and cordyline. If you are after colour use foliage. Gold-leafed plants — Tradescantia ‘Sweet Kate’, Canna ‘Bengal Tiger’ and Golden Pineapple Sage — brighten the dark. Nothing is more psychedelic than Canna ‘Tropicanna’ or pink iresine.
Still you don’t have to give up on flowers completely. Many flowers of the low light rely on scent to attract pollinators. You have the option of the sweet delights of daphne, Ginger Lilies, Sweet Box (Sarcococca confusa), Mexican Orange Blossom (Choisya ternata) and the unsurpassable luculia.
There are also shade lovers beyond the ubiquitous azaleas and camellias that will give colourful blooms. Plectranthus sp. are as tough as boots and flower from white to deep purple. Clivias are probably the showiest of shade flowers. In dappled shade woodland flowers thrive — try columbines, epimediums and oakleaf hydrangeas. Don’t forget bulbs! Daffodils and bluebells are classic deciduous shade plants and veltheimia flowers well under our Moreton Bay Fig at Heronswood.
This is all very well, but as Diggers members you will want something to eat. Growing food crops in shade is a challenge. The usual crop plants need at least 6 hours of sun to produce worthwhile crops. In the darkest shade you should probably give up, but in partial shade there are options. In our food border at Heronswood we have some very shady pockets. Understorey fruits do well: guavas, babaco and Mountain Paw Paw, blueberries and alpine strawberries make for a productive ground cover.
Under our zelkova in the vegetable parterre, rhubarb and Golden Marjoram thrive. Leafy crops like the decorative Blood Sorrel, parsley and coriander boom, given irrigation. You can also get passable root crops of potatoes, radishes and carrots grown in containers in the shade. So you can have your shade and eat it too.
