Water-wise planting around a designer deck

A designer deck that meets a bare fence is a platform. A designer deck that meets planting is a room in a garden. The difference is not a few pots bought on the way home from the board yard. It is a set of arguments — roots against footings, leaf against oil, shade against drying, water against a climate that does not owe you a green July — and a willingness to let the garden be Australian rather than a borrowed cottage.

Water-wise planting is the brief this country actually issues. It is not a look, though it can be a beautiful one. It is the decision to stop pouring drinking water onto a strip of thirsty exotic that sits against the joists and keeps them wet. It is also the decision not to plant a sentimental eucalypt so close to a small deck that the household spends the next decade in the leaf-stain essay.

Roots versus structure

Timber decks fail quietly where the ground meets the frame. Posts, stirrups, inspection zones, the first joist off a garden bed — these are not planting opportunities. They are the reason the platform stays a platform.

Roots follow water and air. A lush bed that is irrigated against a deck edge is an invitation. Roots will find a footing, lift a poorly detailed paver, sit against a post, and make the annual look underneath into an excavation. A hedge planted to hide the undercroft will hide the undercroft from you as well, and from anyone who needs to see termite evidence or a rusting stirrup. Privacy is a real need; a solid green wall hard against the frame is a moisture wall.

Plant the garden. Do not plant the structure. A hedge that hides the posts also hides the first evidence that the posts are in trouble.

Give the structure a gap.

• A clear inspection strip at posts and along the house, even if it is only gravel and a few tough, low plants that do not want a daily drip.
• Beds that fall away from the deck, not toward it.
• Irrigation that does not arc onto boards, joist ends, or the ledger.
• No soil banked against timber. None. This is ordinary construction hygiene and still the most common garden injury to a deck.

On small lots, courtyards and rooftops the pressure to plant against every edge is stronger. Resist the frame. Plant the boundary, plant the pots, plant a bed that is a bed — a contained, lined, drained object — rather than a pile of soil that happens to touch a bearer.

Trees have a longer argument. A tree that will be large wants a setback that still looks generous when the trunk is the trunk you actually get, not the one in the nursery pot. Seek advice that is horticultural and structural if you are planting anything with ambition near a suspended floor. This journal will not give you a species-by-species root map. It will say: the pretty sapling is not the plant. The plant is the thing in fifteen years.

Leaf stain, litter and the romance of the canopy

A canopy over a deck is summer salvation and a maintenance contract. Deciduous shade is the old, good idea: leaf in summer, light in winter, a climate control that does not need a motor. In southern Australia a deciduous tree to the north of a deck can be worth more than an extra metre of roof. In much of the north, evergreen shade is the more honest story, because the sun you want to lose is not only a January problem.

The cost is litter. Leaves in gaps. Tannin on oil. Flowers that become slime. The particular gift of eucalyptus, paperbark, and a dozen other natives that make a garden feel like this country and make a board look like a tea stain. You can have the tree. You cannot have amnesia.

Choose the canopy for the deck you will keep.

• If you will not sweep, do not plant a heavy litterer over the table.
• If you love a eucalypt, put it where the drip is garden, and let the deck take filtered light from the side.
• If you want deciduous shade, prefer a species whose leaf is a leaf, not a wet mat of flower, and give the boards a chance to be cleared before winter.
• Fruit over a dining table is a wasp and a stain. Fruit to the side is a breakfast.

Screens of planting — tall grasses, a clipped native hedge, a loose mix that does the work of a fence — are often kinder than a tree over the floor. They give privacy and shade without the drip line down the middle of the entertaining bay. They still need a gap at the foot so air can move and so the deck edge can dry. A hedge that is watered onto the boards is a mould plan.

Natives, and the other plants that behave like them

“Native” is not a maintenance-free sticker. It is a starting climate. A plant that evolved here often wants less summer water once it is in, and it often looks right against Australian hardwood and Australian light. It may still be short-lived, messy, spiky, or wrong for a tight courtyard. A local provenance, a coastal species on a coastal block, a dry-tolerant plant on a limestone Perth verge — these are more useful than a patriotic genus.

Water-wise exotics exist and can be honest: olives, some herbs, a well-chosen succulent in a pot that is not a gimmick. The test is the tap and the look in February. If a plant needs a weekly soak to look like the photograph, it is a poor neighbour to a deck in a dry city and a poor story in a wet one, where that soak is also a gift to the joists.

Think in layers rather than in specimens.

Canopy, if the block can take it, for the season you need. Screen, for neighbours and for west sun, with a dry foot. Low edge, to stop the deck from feeling like it ends in a cliff of paling, without burying the frame. A few plants you will look at, close enough to the sitting zone that they are part of the room — in pots, if the deck is the only floor they can have.

Avoid the strip of thirsty annuals that must be replaced as a hobby. A designer deck does not need a florist’s foreground. It needs a garden that still looks like a decision in the fourth year.

Pots versus in-ground

Pots are how a deck becomes a garden without asking the ground. They are also how a deck becomes a collection of wet rings and unweathered rectangles. Used well, they are a movable climate: herbs by the kitchen in the season you cook, a screen of bamboo in tubs on a rooftop you cannot plant, a single handsome plant that marks the lounge.

Used poorly, they are saucers of mosquito water, overload on a board, and a moisture patch that never sees sun.

Rules that save argument:

• Lift pots off the boards. Feet, a stand, something that lets the timber dry.
• Do not leave saucers full. In mosquito country this is not optional courtesy.
• Move them through the year so the same boards are not permanently pale and damp.
• Water into the pot, not onto the deck. A slow soak beats a hose that hits five boards on the way.
• Mind the load. Wet soil is heavy. A grove of large pots is a structural conversation on a framed floor, especially on a rooftop.

In-ground beds are the kinder long-term water story if you can build them as beds: an edge, a fall, a soil that is not builder’s fill, a drip line that stays in the bed. They let plants do what plants do — root out, find their own moisture, get past the first summer. They should not be a slope of mulch that washes onto the deck in the first storm, and they should not be a peat-rich mix that you then have to keep wet against the house.

Many of the best Australian decks do both. The ground takes the hedge and the tree. The deck takes the pots that are part of the furniture — the ones you can move when December needs the extra chairs.

Water, irrigation and the deck as a catchment

Water-wise starts with not wasting water and continues with not pointing water at timber. Those are the same project.

If you irrigate, irrigate the plants. Drip in the bed. A hand water for the pots. A system on a timer that still has a rain sensor, or a household that can turn it off when the sky is already doing the work. Spray that mists the undercroft is how you grow film and then decay and then a repair quote.

The deck itself is a catchment. Roofed, it sends water to gutters. Open, it sends water through the gaps. That water can be a resource to a bed if you have thought about it — a chain, a gravel trench, a garden that wants the drip — or it can be a stain line and a wet post. After a wet summer the mould essay is full of what happens when water sits. Planting should make sitting less likely, not more: no dense groundcover over a joist bay, no swale toward the house, no fashionable “naturalistic” mess piled against the stair.

Greywater and tank water have their own rules and their own chemistry. Do not invent a system from a social post and run it under a deck. If you have a useful tank, give the garden the overflow in a place that can take it. If you have no tank, choose plants that can live on what the sky and a stingy tap will give.

A brief that keeps the deck honest

Write the planting as you would write the furniture: around how the room is used.

The dining bay wants light and a floor you can sweep. The lounge can take a closer plant, a scent, a pot that is part of the sitting. The service edge can take the tougher hedge. The stair wants to be seen. The posts want to be seen once a year with a torch.

Then write the climate: your rainfall, your restrictions, your soil, your salt, your frost. A water-wise plant in Hobart is not a water-wise plant in Adelaide. A coastal native on a red-soil Brisbane slope is a different conversation again. Local knowledge — a nursery that still knows plants, a landscape designer who has kept a garden alive through a restriction summer — is worth more than a generic list of “natives for decks”.

The last test is late February, late in the afternoon. The boards should still look like timber, not like a compost print. The plants should look like they live here, a bit tired perhaps, not like they are on a drip in a salon. The gap at the frame should still be a gap. If you can sit, and the garden is doing the work of a wall and a shade and a kindness, and you have not spent the month watering a regret, the planting is doing its job. That is all a designer deck asks of a garden: to belong to the same climate, and not to eat the floor.