Auditing an existing garden: keep, kill, or salvage

Renovating is harder than starting from bare sand, because you must judge what is worth keeping. A structured audit of every plant, surface, structure and system — with a verdict and a reason for each.

⏱ 90 minIntermediate🔗 8 resources (8 free)

Anyone can design a garden on bare sand. The hard version is the one you have: a block with twenty years of other people’s decisions already built into it. Some of those decisions are worth keeping. Most are not.

The failure mode this lesson prevents is leaving things undecided. An element with no verdict is an element you end up working around, and working around things is where renovation budgets go.

What a professional does at this stage

A landscaper walking an established block is not admiring the garden. They are pricing removal.

Every existing element is either an asset that reduces the build cost, or a liability that adds a demolition, disposal and make-good line to the quote. There is no third state. A sound limestone retaining wall saves you a fortune; the same wall bulging at mid-height is a rebuild plus the excavation to reach it.

So the verdict gets made on the first walk, and the reason gets written down. The reason matters more than the verdict, because the reason survives when the design changes.

Verdict	Means	The test
KEEP	Stays exactly where it is	It works, it has years left, and it does not obstruct anything you want to do
RELOCATE	Has value, wrong place	Worth more than the cost of moving it, and it will survive being moved
REPLACE	Right idea, failed execution	The function is still needed, the thing itself is at end of life
REMOVE	Goes, nothing comes back	The function is not wanted, or it is a hazard or a legal problem

Force a verdict on everything. If you genuinely cannot decide, write KEEP with a condition — “keep pending arborist”, “keep unless the alfresco moves west”. That is a decision. “See how we go” is not.

Plants

Inventory everything over knee height; below that it will be disturbed by the works anyway. Record species (or a photo), rough height and spread, and a condition rating out of five. Then the question that actually decides it: is this plant doing a job in the new garden? Shade on the western wall, screening a neighbour’s window, holding a bank together. A healthy plant doing no job is still a REMOVE.

Three Perth specifics change verdicts here:

Most established plants here do not transplant. Deep sand grows deep, sparse root systems with no fibrous mass to lift. Anything over about 1.5 metres that has been in the ground three or four years is KEEP or REMOVE, not RELOCATE. Small shrubs, clumping plants, agaves and grasses move fine.
Relocate in winter. May to July, into moist soil, cut back hard, shaded afterwards. A summer relocation on the Swan Coastal Plain is an expensive way to kill something.
Check the weeds against the declared list. Some escapees in an old Perth garden carry a legal control obligation, not just a nuisance rating.

Do not try to judge a significant tree from the ground here. Flag it and carry it into the tree assessment lesson.

Hard surfaces: judge the base, not the surface

This is where renovation quotes go wrong by five figures.

A paved area is two systems: the pavers you can see, and the compacted base nobody has looked at since it was laid. They fail independently and cost completely different amounts to fix. Cosmetic failure — efflorescence, staining, moss, weeds in the joints, a couple of cracked units — means cleaning, swapping units and re-sanding. Cheap. Base failure looks like this:

Dips or ruts that follow a line — a wheel track, a path, a trench — rather than one paver
A depression still holding water fifteen minutes after the rain stops
Pavers that rock or click underfoot
Joint sand that keeps disappearing however often it is topped up, because it is washing down into voids
Rows fanning out at the perimeter, or wedge-shaped gaps opening, meaning the edge restraint has failed
A stepped level change along an old service trench, a soakwell lid, or a ground-out stump

Then confirm it. Lift four to six pavers at the worst spot with two flat screwdrivers or a paver puller, and look at what is underneath:

Bedding sand depth. It should be a consistent 25 to 30 mm. Find 60 to 80 mm and someone used bedding sand to correct a badly levelled base. That will keep settling.
Is there a base at all? Push a screwdriver into the layer below the sand by hand. If it goes in easily, the pavers were laid on fill. Common on Perth blocks, especially builder-laid paths and side access.
What it is, and how thick. Perth standard is compacted crushed limestone, which self-cements when laid in layers and compacted wet — roughly 100 mm compacted for foot traffic, more for a driveway.
Contamination. Roots, mud, grey slurry, or fines pumped up into the bedding sand all mean water and movement.

The decision rule: under about 10% of the area affected, with matchable pavers, is a KEEP with a local lift-and-relay. Widespread failure, or no base at all, means the pavers themselves are still the valuable part — stockpile them, rebuild the base properly, relay. That is REPLACE the base and KEEP the surface, and your audit should say exactly that. Carry the numbers into base preparation and paving.

Poured surfaces are less forgiving. Hairline crazing in liquid limestone or exposed aggregate is cosmetic. A crack with a level change across it, or a slab that rocks, is structural — and concrete cannot be lifted and relaid. KEEP or demolish.

Testing the retic station by station

Never write “retic works”. Test it station by station and record the faults per station.

Water Corporation permits running each station for two minutes for testing, on your rostered days, before 9am or after 6pm. The winter sprinkler switch-off runs 1 June to 31 August and applies to bore water as well — if your audit falls in that window, a Waterwise Garden Irrigator can legitimately test outside the restrictions.

Baseline the meter. Everything off, read it, wait fifteen minutes, read again. Movement means a leak before you have run anything.
Document the controller. Brand, model, station count, and photograph the existing program before you change it — it tells you how the garden has actually been watered.
Find the valve boxes. Map them. Plenty of Perth systems have solenoids buried with no box at all; probe along the mainline with a long screwdriver.
Run each station and stand in the zone while it runs.

Per station record: does it come on at all; how many heads and what type; heads not popping up, stuck down, buried, tilted or blocked by growth; misting (over-pressure) or dribbling (under-pressure); overspray onto paving or the fence; whether the valve actually shuts off; and whether water keeps draining from the lowest head after shutdown.

Two faults change the verdict rather than being repairs:

Mixed head types on one station. A spray head applies 35 to 45 mm per hour, a rotary 10 to 15. On the same valve, one of them is always wrong. That is re-valving, not repair.
Lawn and garden bed on one station. Different rates, different schedules. Also a redesign.

Then catch-cup your two most important stations: six to eight straight-sided containers spread across the zone, fifteen minutes, measure each with a ruler. If the driest holds less than half the average, that station cannot be scheduled sensibly — you would have to drown everything to keep the dry corner alive.

Finally, compare the controller run times to the published rates. A rotary station set to 10 minutes has been delivering roughly 2 mm, not 10 mm, for years. That one line often explains a garden’s condition better than the soil does.

If there is a bore, add pump start and cut-out, flow, and iron staining. Orange staining on limestone and paving means iron in the water, and iron progressively blocks drip emitters — which rules out converting those beds to dripline without treatment.

The hazards and the legal problems

Walk the block once more looking only for these. They are not design decisions and they do not wait for the design.

Asbestos. Super six fencing and fibro sheds are everywhere in pre-1990 Perth suburbs. More than 10 square metres of non-friable material is licensed removal work.
Pool barriers. Anything you build near an existing pool fence can break compliance, and councils re-inspect at least every four years. See pools and pool fencing.
Retaining walls. Bulging, leaning, cracked, or with no visible drainage — see retaining walls approval.
Structures with no paperwork. Patios, sheds and decks built by a previous owner. Their status affects what you are allowed to add.
Unknown services. Old power to a shed, unmarked poly, an abandoned soakwell. Cross-reference with locating services.

What happens to this next

KEEP and RELOCATE items become fixed points on the concept plan — constraints you design around. REPLACE and REMOVE items become the first real numbers in your budget, because demolition and disposal are costed by volume and by trade, and quantity take-offs will ask you for them.

The next lesson takes every tree you flagged and assesses it properly — health, structure, root zone, and what it is actually worth to keep.

Do this on your own block

Field journal entry

Existing garden audit

List every existing element on your block — each significant plant, paved area, structure, edge, and the retic system. For each: condition, remaining life, cost to keep versus cost to replace, and a verdict of KEEP, RELOCATE, REPLACE or REMOVE, with the reason.

Checklist

Inventory every plant over knee height with a condition rating
Assess each hard surface for base failure, not just surface appearance
Test the existing retic station by station and record the faults
Give every element a verdict and a one-line justification
Identify anything that is a hazard or a legal problem

Where to go deeper

Every link below was fetched and checked before it shipped. Nothing here is a guess.

Freegovernment10 minPerth / WA
Irrigation and sprinkler testing
Water Corporation
Why this oneThe official method for testing a Perth retic system without breaching the sprinkler roster. It gives the meter-baseline test for hidden leaks, the sequence for isolating a fault between the master valve, the zone solenoids and the zone pipe, and the rule that matters most during an audit — you may run each station for two minutes for testing purposes, on your rostered days, before 9am or after 6pm. It also explains that a waterwise garden irrigator can test outside those windows, which is the legitimate way to audit a large system in one visit.
Link checked 2 Aug 2026
Freecalculator5 minPerth / WA
How long should I run my sprinklers for
Water Corporation
Why this oneThe published application rates for each sprinkler type, which is what turns a catch-cup reading into a verdict. Pop-up and fixed spray apply 35 to 45 mm per hour and need 13 to 16 minutes to deliver the 10 mm target; rotary heads apply 10 to 15 mm per hour and need 40 to 60 minutes; gear drive rotary 30 to 40 minutes; dripline 30 to 40 minutes. Compare those to what the existing controller is actually set to and you often find the real reason a garden has been declining.
Change this for Perth
The 10 mm per watering day target is a Perth and Peel default for a two-day roster on sandy soil. It is a scheduling starting point, not a plant water requirement — hydrozoning changes it, and this course revisits the number in Phase 8.
Link checked 2 Aug 2026
FreedirectoryPerth / WA
Find a Waterwise Programs Specialist
Irrigation Australia / Water Corporation
Why this oneThe searchable list of Waterwise Garden Irrigators, Waterwise Irrigation Design Shops and rebate-approved businesses, run by Irrigation Australia as the national industry body and tied to the Water Corporation programs. If your audit finds a system you cannot diagnose, this is the filter that separates endorsed irrigators from the general retic trade, and only businesses on this list can process the Water Corporation rebate.
Change this for Perth
Endorsement means the business has been appointed to deliver the program, not that it is the cheapest or the best designer. It also lists Victorian members, so filter by state.
Link checked 2 Aug 2026
FreegovernmentPerth / WA
Waterwise Irrigation Rebate
Water Corporation
Why this oneTwo of the most common faults an audit turns up — a hidden pipe leak and a failed solenoid valve — are exactly what this rebate covers, and every rebated service includes a controller check and adjustment. The rebate is up to $200 credited to your Water Corporation account, so if you are about to pay someone to diagnose your retic anyway, doing it through a listed irrigator can return most of the call-out fee.
Change this for Perth
Checked in August 2026, the published round ran from 1 September 2025 to 31 May 2026 for Perth and Peel Water Corporation account holders with a system that has watered in the last two years. The program runs in annual rounds and allocations can be exhausted early, so confirm the current round dates and eligibility before you book the work.
Link checked 2 Aug 2026
Freearticle40 minOverseas — adapt it
Operation and Maintenance Guide for Interlocking Concrete Pavement (PAV-TEC-006)
Concrete Masonry and Hardscapes Association
Why this oneThe best free document on telling a cosmetic paving problem from a structural one. It works through eleven named distresses — rutting, joint sand loss, efflorescence, damaged units and the rest — and separates the ones you clean or top up from the ones that mean the base has moved. It then covers subgrade compaction, base replacement, geotextile and the correct way to lift and reinstate pavers, which is the repair you will be costing if your audit says the surface is salvageable but the base is not.
Change this for Perth
North American document. Ignore the freeze-thaw material entirely — it does not apply here. Substitute compacted crushed limestone for the crushed aggregate base it describes, since that is the Perth standard, and read its drainage warnings as being about compaction rather than saturation, because a Perth sand subgrade drains fast. Base failure in Perth is almost always poor compaction, an uncompacted service trench, or no base at all.
Link checked 2 Aug 2026
Freegovernment15 minPerth / WA
Swimming pool and spa safety barrier requirements
Building and Energy, Department of Energy, Mines, Industry Regulation and Safety
Why this oneThe regulator's own page, and the one to read before you plan anything near an existing pool. It sets the trigger at water more than 30 cm deep, names the applicable standards (AS 1926.1-2012 and AS 1926.2-2007 for barriers installed after 1 May 2016), and confirms that local governments must re-inspect private pool barriers at intervals of no more than four years. Raising a garden bed, adding a step or moving a gate beside a pool fence can quietly break compliance, and this tells you what compliance means.
Link checked 2 Aug 2026
Freegovernment20 minPerth / WA
Asbestos law and guidance
WorkSafe WA
Why this oneThe regulator's statement of the removal thresholds, which is the number you need before you decide whether that super six fence or fibro shed is a demolition line item or a licensed-contractor line item. A licence (Class A or B) is required to remove more than 10 square metres of non-friable asbestos-containing material, and any amount of friable material requires a Class A licence. Anything built in WA before the mid-1980s should be assumed to contain asbestos until proven otherwise.
Change this for Perth
These are the work health and safety thresholds that bind anyone doing the work for fee or reward. A homeowner working on their own home also has duties under the Health (Asbestos) Regulations 1992 and must dispose of the material at a facility licensed to accept it — ask your local government environmental health officer before you touch it.
Link checked 2 Aug 2026
Freegovernment15 minPerth / WA
Declared weeds in Western Australia
Department of Primary Industries and Regional Development (DPIRD)
Why this oneSome of what is growing in an old Perth garden is not merely unwanted, it is a declared pest you are legally obliged to control. This page explains the C1 exclusion, C2 eradication and C3 management categories under the Biosecurity and Agriculture Management Act 2007, notes that ornamental escapees such as boneseed and pokeweed are on the list, and links to the Western Australian Organism List where you can search any plant by common or scientific name and get its legal status.
Change this for Perth
Declared status is a legal category, not a horticultural one. Plenty of genuinely invasive Perth garden plants are not declared and still deserve a REMOVE verdict.
Link checked 2 Aug 2026

The rules, with sources

WA regulation changes. Each point below names its primary source and the date it was last checked — always confirm with your own council before you build.

Sprinklers must not be used in Perth, Mandurah and parts of the South West between 1 June and 31 August each year. The winter sprinkler switch-off applies to bore water users as well as scheme water users, and the standard fine is $100.
Water Corporation ↗ · checked 2 Aug 2026
A garden bore does not require a licence if it irrigates less than 0.2 hectares (2,000 square metres) and is not used commercially, but bore users in Perth and Mandurah must still follow the two rostered watering days per week and water before 9am or after 6pm.
Be Groundwater Wise, Department of Water and Environmental Regulation ↗ · checked 2 Aug 2026
Pools and spas containing water more than 30 cm deep must have a compliant safety barrier, and local governments must inspect private pool and spa barriers at intervals of no more than four years.
Building and Energy, Department of Energy, Mines, Industry Regulation and Safety ↗ · checked 2 Aug 2026
A Class A or Class B licence is required to remove more than 10 square metres of non-friable asbestos-containing material, and a Class A licence is required to remove any amount of friable asbestos-containing material.
WorkSafe WA ↗ · checked 2 Aug 2026
Where a plant is a declared pest under the Biosecurity and Agriculture Management Act 2007, the owner or occupier of the land is obliged to control it. Control categories are C1 exclusion, C2 eradication and C3 management, and status can be checked on the Western Australian Organism List.
Department of Primary Industries and Regional Development (DPIRD) ↗ · checked 2 Aug 2026