Garden Guru: Sunny side of life

Clematis Pillu likes its head in the sun and its feet in the shade. Photo / Supplied

Why don't garden centres segregate their stock and drop the practice of an A to Z of shrubs?

It would be far more useful if - just as some old-fashioned schools had separate entrances for girls and boys - the plants we buy could be separated into those which love to lurk in shadows, those which like to bask in the sun, and a corner for the in-betweens.

A plant's preference for light is fundamental to its success. New plants aren't cheap so it's vital to give them the best conditions you can.

Availability of light seems a basic thing but many of us keep getting it wrong. Even passionate horticulturists forget that many a plant which started life shimmering in sun may, some years later, find itself in a dim jungle as neighbours have burgeoned over the years and drawn a veil over the available light.

In a good garden plants are naturally re-housed as the light conditions change.

So, as we head into prime planting time, whether it's introducing new plants to your patch or shuffling your existing ingredients, this is the perfect chance to make amends and get your plants to the places they belong.

A good start is to understand your site. Any house walls, fences or hedges facing north will catch the sun for most of the day while south-facing boundaries are the shadiest.

When I design gardens it's surprising how often a client cannot even tell me where the sun rises and sets. East and west walls have sun for only half the day at the most so these are the places to use plants such as Japanese maples and hydrangeas, which like sun but not for the whole day.

Some plants insist on sun or shade but a larger proportion can cope with a little of both. Many so-called shade plants, such as hostas, will cope in much brighter conditions if kept well hydrated.

The same cannot be said for the sun-worshippers, many of which will sulk or refuse to flower in low light.

Before moving a plant from a site where it appears to be unhappy, first look at ways you can change the light conditions. For example, heightening or thinning a tree canopy may make all the difference.

Bear in mind that the sun is nearly always hitting your garden from an angle. Even under a tree, if you have lifted its canopy, toward the north side plants will receive plenty of sun. But shadows cast by larger shrubs and trees can sometimes mean that even the open large areas of gardens may be in shadow for much of the day.

Shade is sometimes seen like the jail corner on the Monopoly board, a place to scoot past as quickly as possible. But there are almost as many shade-loving plants as sun-lovers, and in shade colours can seem more intense.

The deepest shade is cast by the canopy of evergreen trees and by tall buildings - you will need tough jungle-like plants with deep green leaves to cope in such places - such as clivia, aspidistra, micropiper and pseudopanax.

The telltale sign that a plant is not liking a shady corner is that its foliage will be meagre. And a lack of flowers or variegation are classic signs of too little light. Some bromeliads lose their bright leaf colours, golden choisyas turn green, and perennials and bulbs grow tall and flop in their search for more light.

Shady places can often also be dry so make sure you either irrigate or choose tough specimens.

Dedicated sun-lovers include most alpine plants, many Mediterranean, desert and coastal plants and natives such as pittosporum and hebe - that may make them potentially bad subjects for hedges because if those hedges happen to run east to west the south side will always lose sun and the hedge will get threadbare on one side.

The simple act of planting rows of plants such as vegetables in a north/south direction will mean that both sides of the rows get their share of the light. Plants that like shade in the day - such as gardenias, skimmias and daphnes - often show their displeasure in full sun by turning yellow. This is often mistaken as a nutrient deficiency and in severe cases leaves will get scorched and turn white and papery on the edges - a common sight in maples planted in open, windy places.

In every plant family there is an exception to the rule.

Euphorbias are generally considered sun-lovers but Euphorbia amygdaloides var robbiae is a welcome exception because it makes a great groundcover for dry shade.

Almost all members of the protea family need well-lit and ventilated conditions to echo their native habitat. Our native rewarewa tree (Knightia excelsa) is an exception to the rule - its beautiful exotic flowers go almost unnoticed in native forests and don't mind all the shade around - trust a New Zealander to want to do things differently.

Could do this week

* Sow wildflowers to replace boring stretches of lawn.

* It is planting time so look out for where you need to fill gaps.

* Empty old compost heaps so you can use the contents to dig into planting holes.

* Complete the renovation of tired lawns and fertilise with a dedicated autumn lawn food.

* Strawberries planted now in a well manured spot will establish through winter and be ready to yield fruit next season.

* Take semi-hardwood cuttings of favourite shrubs such as lavender.

* Divide overcrowded perennials.