Glossary of garden terms

83 terms as they are used in this reference and in Australian gardening generally. Definitions are deliberately short. Where a term has a broader technical meaning elsewhere, the definition here is the practical garden one.

• A
• B
• C
• D
• E
• F
• G
• H
• L
• M
• N
• O
• P
• R
• S
• T
• V
• W

A

Acid soil

Soil with a pH below 7. Many Australian natives and camellias prefer slightly acid conditions; most vegetables tolerate a range around neutral.

Aeration

Physically opening compacted soil so air and water can move through it, usually by pushing a garden fork to full depth at regular intervals and levering gently.

Alkaline soil

Soil with a pH above 7, common in arid and calcareous districts. Some plants show yellowing between leaf veins in alkaline conditions because iron becomes less available.

Annual

A plant that germinates, flowers, sets seed and dies within one growing season.

Aspect

The direction a bed, wall or slope faces. Aspect decides how much sun a position gets and at what time of day, and it matters more than most people allow for.

B

Bare-rooted

Deciduous stock sold dormant in winter with no soil around the roots. Cheaper and lighter than potted stock, and it establishes well provided it is planted while still dormant.

Basin

A shallow saucer-shaped depression built around a plant to catch and hold water so it soaks in rather than running off. Standard practice in arid gardens.

Biennial

A plant that grows leaves in its first year, then flowers, sets seed and dies in its second.

Bolting

Running prematurely to flower and seed, usually triggered in vegetables by heat, dry soil or day length. Bolted lettuce and brassicas turn bitter and stop producing usable leaf.

Botanical name

The two-part scientific name of a plant: genus with an initial capital, species in lower case, both in italics. It identifies a plant unambiguously where common names do not.

Broadcast

Scattering seed evenly over a prepared surface rather than sowing it in rows or individual holes.

Bud

A compressed shoot that will become a leaf, a stem or a flower. Where the buds sit and when they form determines when a plant can be pruned without losing flowers.

Bulb

An underground storage organ made of fleshy leaf bases, from which the plant regrows each season.

C

Cambium

The thin layer of actively dividing tissue just under the bark. Damage that rings a trunk and cuts the cambium all the way around will kill the plant above that point.

Canopy

The spreading upper structure of a tree or large shrub, and the area of ground it shades.

Clay

Soil made of very fine particles that hold water and nutrients well but pack tightly, leaving little air space. Its problem is structure rather than fertility.

Collar

The slightly swollen ring where a branch joins a trunk. Removing a branch just outside the collar allows the wound to close; cutting flush with the trunk removes the tissue that does the closing.

Collar rot

Decay at the base of a stem or trunk, most often caused by mulch or soil piled against the bark so that it stays permanently damp.

Compaction

Soil pressed together so that pore space is lost, usually by foot traffic, mowing wet ground or construction machinery. Roots do not enter compacted soil.

Companion planting

Growing different species together in the belief that one benefits another. Evidence varies considerably by combination; treat specific claims with caution.

Compost

Organic material broken down by microbial activity into a dark, crumbly, stable product used to improve soil structure and water holding.

Contour

A line of constant elevation across sloping ground. Swales and planting rows run along the contour so that water is slowed and spread rather than concentrated.

Cool-season grass

A lawn grass, such as fescue or ryegrass, that grows in the cooler months and struggles through hot dry summers. Grown from seed rather than spreading by runner.

Crown

The point where stem meets root at soil level. Burying the crown of a clumping plant under mulch or soil causes it to rot.

Cultivar

A named plant variety selected and maintained in cultivation, written in single quotes after the botanical name.

D

Deciduous

Losing all leaves for part of the year, usually winter. A deciduous tree on the northern or western side of a building shades it in summer and admits sun in winter.

Deep watering

Applying water slowly and for long enough to wet the soil profile to around 300 mm, which draws roots downward. The opposite of frequent light sprinkling.

Dispersive clay

Clay whose particles separate in water rather than holding together. It is the type of clay that gypsum improves; stable clay is unaffected by gypsum.

Division

Propagating and renewing a clumping plant by lifting it, cutting it into sections, discarding the exhausted centre and replanting the vigorous outer pieces.

Dormancy

A period of suspended growth, in winter for deciduous plants and in the dry season for some tropical species. A dormant plant does not need feeding.

Drip line

The outer edge of a tree's canopy, and the point on the ground where most of the active feeding roots sit. Trees are watered here rather than at the trunk.

E

Espalier

Training a plant flat against a wall or frame in a defined pattern, usually to save space or to use the warmth of a wall.

Establishment

The period, usually about two years for a shrub, during which a newly planted specimen builds a root system. Every plant needs regular water through establishment regardless of its long-term water need.

Evergreen

Holding foliage year round. Individual leaves are still shed and replaced, but the plant is never bare.

F

Fibrous roots

A dense mass of fine roots near the surface, characteristic of grasses and mat-rushes and the reason they are effective at holding soil on slopes.

Formative pruning

Pruning a young tree or shrub in its first few years to establish good structure, while the cuts are small and the wounds close quickly.

Frost pocket

A low or enclosed part of a garden where cold air pools on still nights, often several degrees colder than ground a short distance uphill.

Frost tolerant

Able to survive light to moderate frost without protection in an average winter. It is not a guarantee against severe frost on an exposed site.

G

Genus

The first part of a botanical name, grouping closely related species. Plural genera.

Green manure

A crop grown specifically to be dug in or cut down and left on the surface, adding organic matter and protecting bare soil over a fallow period.

Groundcover

A low spreading plant grown to cover bare soil. It functions as living mulch, moderating soil temperature and suppressing weed germination.

Gypsum

A mineral soil conditioner that improves structure in dispersive clays only. It has no effect on stable clays, so it is worth testing before buying.

H

Habit

The characteristic shape and growth pattern of a plant: upright, weeping, prostrate, spreading, clumping.

Hardening off

Gradually acclimatising seedlings raised indoors to outdoor conditions over a week or so before planting them out.

Humus

The stable fraction of decomposed organic matter in soil, responsible for much of its structure and water-holding capacity.

Hydrophobic soil

Soil that repels water, common in sandy soils after a dry summer. Water beads on the surface or runs off while soil below stays dry.

L

Leaching

The loss of nutrients washed downward past the root zone by water. It happens fastest in sandy soils and during heavy rain.

Leaf mould

Composted autumn leaves. Low in nutrients but excellent for soil structure and moisture holding, and it needs no turning.

Loam

A balanced soil of sand, silt and clay that holds moisture while still draining. What most general garden advice quietly assumes you have.

M

Microclimate

Localised conditions within a garden that differ from the general climate: a hot west wall, a shaded southern strip, a frost pocket at the bottom of a slope.

Mulch

A layer of material spread over soil to reduce evaporation, moderate soil temperature and suppress weed germination. The working depth is 50 to 75 mm.

N

Node

The point on a stem where a leaf or bud is attached. Pruning cuts are made just above a node.

O

Organic matter

Plant and animal material in various stages of decomposition. It improves every soil type, and it must be replaced regularly because it breaks down.

P

Perennial

A plant that lives for more than two years, whether woody or herbaceous.

Permeability

In a windbreak, the proportion of air that passes through rather than over. Around 40 to 50 per cent gives the longest and calmest sheltered zone.

pH

A measure of acidity or alkalinity on a scale where 7 is neutral. It affects which nutrients are available to plants rather than how much of them is present.

Pore space

The gaps between soil particles, which hold air and water. Clay soils and compacted soils lack it, which is why roots struggle in them.

Prostrate

Growing flat along the ground rather than upright.

R

Raised bed

A bed built above the surrounding ground level, usually 200 to 300 mm, so that the root zone sits above soil that stays saturated.

Reactive clay

Clay that swells when wet and shrinks when dry. The resulting ground movement is what damages footings and paving, and it affects how far from buildings trees can be planted.

Rhizome

A horizontal underground stem from which new shoots and roots arise. Plants that spread by rhizome fill in over time and need an edge to work against.

Root ball

The mass of roots and soil that comes out of a pot or, for bare-rooted stock, the root system itself. Planting holes are dug twice as wide as the root ball and no deeper.

Runner

A horizontal stem running along the soil surface that roots at intervals to form new plants. Warm-season lawn grasses spread this way.

S

Sand

Soil made of coarse particles that drains fast and holds little water or nutrient. It is improved by organic matter added every season.

Scarifying

Cutting through built-up thatch in a lawn to remove it, done in late spring when the grass is growing strongly enough to recover.

Semi-hardwood cutting

A cutting taken from the current season's growth once it has begun to firm up, usually in summer and early autumn.

Slow-release fertiliser

A fertiliser formulated to release nutrients gradually over months rather than all at once, reducing the risk of burning roots and of loss to leaching.

Species

The second part of a botanical name, identifying a particular kind of plant within a genus. Always lower case, always italic.

Standard

A plant trained to a single clear stem with a head of foliage on top.

Subsoil

The denser layer beneath the topsoil, often clay. It determines how quickly water drains away from the root zone.

Swale

A shallow depression running along the contour of a slope, used to slow and spread runoff so that it soaks in rather than running off.

T

Thatch

A spongy layer of dead stems and runners that builds up between the growing lawn and the soil. Excessive thatch stops water reaching the soil.

Thinning

Removing whole stems or branches at their point of origin to open a plant to light and air, as distinct from shearing the outside.

Tip pruning

Removing only the soft growing tips of shoots. It is the safe pruning method for fine-foliage natives, most of which will not reshoot from bare wood.

Top-dressing

Spreading a thin layer of screened soil or compost over a lawn or bed, no more than about 10 mm at a time, to level minor hollows.

Topsoil

The upper layer of soil, typically around 150 mm deep, containing most of the organic matter, soil life and feeding roots.

Transpiration

The loss of water vapour from leaves. It increases sharply in wind and dry air, which is why wind dries plants faster than heat alone.

Tussock

A grass that grows as a dense discrete clump rather than spreading.

V

Variegated

Having leaves marked with more than one colour. Variegated forms generally grow more slowly than plain-leaved ones and often scorch more readily in strong sun.

W

Warm-season grass

A lawn grass, such as couch, kikuyu, buffalo or zoysia, that grows through the warm months, spreads by runner and goes dormant and straw-coloured in cold winters.

Water shoot

A vigorous, weak, upright shoot produced in response to hard pruning. It is a sign that too much was removed at once.

Waterlogging

Soil saturated for long enough that air is displaced from the pore space. Roots suffocate, and the symptoms closely resemble drought.

Windbreak

A permeable planting used to slow wind rather than block it, sheltering a distance downwind of roughly ten to twenty times its own height.