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Glossary of terms

Glossary of terms

JERRY COLEBY-WILLIAMS explains common gardening and natural pest and disease terms that will make reading our magazine and other gardening information easier. It will also mean you can speak with more assurance when asking for products and plants at garden centres.


General gardening

Acid soils have pH readings less than about pH 6.5 (see pH entry in this glossary). Acid conditions are preferred by lime-hating (ericaceous or calcifuge) plants. The majority of Australian soils tend to be acidic and may be improved by cultivation and the addition of lime or dolomite.

Aerobic Usually describes a characteristic of compost heaps where composting is primarily driven by organisms living or occurring only in the presence of oxygen.

Alkaline soils have pH readings above pH 7.4 and contain relatively more lime. They suit lime-loving (calcicole) plants including many vegetables, especially the cabbage family (brassicas) and the onion family. Alkaline soils are harder to make more acid, although the addition of compost, pine needles, bark mulches, iron chelates and iron sulphate can lower the soil’s pH.

Anaerobic Usually describes a characteristic of compost heaps where composting is primarily driven by organisms living or occurring where oxygen is limited or absent.

Arborist A specialist who cares for and maintains trees, including planting, pruning, identifying and treating trees in ill health. Sometimes confused with tree loppers, who are unqualified amateurs.

Bolting is when a plant flowers prematurely, often as a result of drought, malnourishment or high temperatures.

Broadcasting involves sowing seed, such as salad vegetables, by hand evenly over a prepared seed bed. Seed is lightly raked into the surface, watered in, or covered with a veneer of sieved soil or mulch.

Bulb This is an underground food storage organ, generally perennial and generally looking like a large bud enclosed in overlapping scales, such as a lily bulb. Often misapplied to include corms, tubers, rhizomes and other underground food storage organs.

Backfilling The task of replacing soil excavated from a planting hole after planting.

Blanch A traditional technique where sunlight is kept away from stems and leaves of food plants, such as celery and cardoon, which keeps their tissue pale, soft and makes it more palatable.

Catch crops such as green manures and salad vegetables, including radish, grow rapidly on soil that would otherwise be left empty between primary crops.

Compost is either made at home from decomposed garden refuse, or purchased as a ready to use product.

Hot composting – by making one cubic metre of compost at one time, the heap generates enough heat to kill weeds, seeds and bulbs.

Cold composting – Garden refuse is allowed to decompose on its own. Cold composting doesn’t destroy seeds, weedy bulbous plants or fungal or bacterial pathogens. These must be dealt with separately.

Bought compost may also contain fertilisers, including poultry manure, or they may be bulked up using inexpensive products such as sand, or semi-composted products such as bark. Look for certified organic composts and manures at hardware stores, nurseries and garden centres.

Compost tea A liquid fertiliser made by mixing matured compost with water and filtering out debris. Premium quality compost tea is fermented in an aerated container before use.

Cover crop Plants such as millet or barley sown to protect cultivated land from stormwater erosion or to suppress weeds between normal sowing seasons.

Corm This is an underground food storage organ composed of a thickened stem section with a protective skin, or tunic. Planted like bulbs, successive corms develop from the parent corm during the growing season.

Crocks are broken pieces of terracotta pot used to cover drainage holes in the bottom of pots. They minimise the loss of compost during watering while allowing drainage. The term is commonly misapplied to stones or large pieces of bark used for a similar purpose, but stones and bark can block drainage holes and cause root rotting due to saturated compost.

Culm A botanical term for the stem of bamboo, which is a member of the grass family.

Cutting A cutting is a section of a root, stem, or leaf used to propagate a new plant complete with its own roots.

Deadheading The practice of removing flowers as they fade to prevent the plant from wasting valuable energy on forming seeds and for keeping plants looking tidy. Deadheading extends the life of annuals and can prolong the flowering of shrubs and roses.

Division A way of multiplying a plant by cutting or pulling a large clump into smaller portions.

Deciduous A term applied to trees and shrubs that shed all their leaves during the resting period. Most commonly applied to autumn and winter deciduous plants, although this also applies to plants adapted to shed their leaves during summer or autumn drought, such as the strangler fig.

Espalier A space-saving method of training a tree or shrub to grow multiple horizontal side branches against a wall or other support. Pear and apple trees are common and suitable subjects.

Evergreens Plants that retain their leaves all year round or almost all year round. Evergreens may also continue growing slowly in winter. Evergreens may either shed some of their older leaves through the year, or suddenly shed their leaves and rapidly develop fresh leaves as a new growing season begins, as in the avocado.

Foliar feed Also known as foliar fertiliser, this is a liquid solution containing water-soluble fertiliser, such as seaweed, which is sprayed on the foliage of a plant so that it can absorb the nutrients directly through its leaves.

The technique is sometimes used to feed small plants growing under hungry trees. Foliar spraying prevents the tree’s roots taking all the nutrients. Many products are available commercially.

Grafting A technique in which two or more different woody plants, generally trees and shrubs, are combined by joining cuttings. Usually this involves an adaptable rootstock and a prolifically flowering or fruiting topstock. Graft incompatibility sometimes gradually occurs where different plant tissues do not thoroughly unite.

Green manure A crop (such as lentils or barley) grown and then dug into the soil at a juvenile stage to increase soil fertility or organic matter content. Usually dug in a few weeks before the site is planted with another crop.

Grey water This is water produced by sinks, baths, washing machines and showers. Some authorities class grey water obtained from washing machines, baths and showers as black water on the assumption that they are heavily contaminated with faecal matter. Grey water that contains green cleaners and is free of fats and oils may be used treated or untreated in horticulture, although government regulations for its use vary greatly.

Gypsum A mineral of calcium sulphate. Gypsum adds calcium to the soil, reducing the likelihood of blossom end rot, and improves the structure and workability of most clay and saline (sodic) soils. Gypsum does not alter the soil pH.

Hardening off  involves gradually acclimatising plants to outdoor conditions so they can survive without harm from heat, frost, wind or sunshine. Usually practised when taking seedlings and plants out of protected cultivation in a glasshouse, shadehouse or igloo.

Heirloom or heritage plant Plants that have generally been around for 50 years or more. Not all people will consider the same plant an heirloom (see also “Open pollinated”).

Heirloom tomatoes are a beautiful addition to your garden and full of flavour.

Herbaceous Soft-stemmed, not woody, perennial plants. Winter herbaceous perennials die down in autumn and winter and reshoot in spring from their resting buds.

Inorganic A chemical or fertiliser that is not obtained from a source which is, or has been, alive.

Intercropping A technique sometimes also known as interplanting, where two or more plants, for example tall and short, are grown together to maximise the productivity of land, or to enjoy their contrasting form and colours, or to extend the flowering or cropping season of either productive or ornamental plants. Corn and beans are a good example.

Manure tea A liquid fertiliser made like compost tea, only using well rotted manures and mixing them with water and filtering out any debris. Woven or hessian sacks or old pillow cases filled with cow or horse manure can be steeped in a container of water.

Micronutrients Also known as trace elements, these are very important in small quantities for plant health. It is easy to overapply trace elements, such as boron, and this can have equally serious consequences for plant health as a deficiency does. Most Australian soils are ancient (fossil) soils and are generally deficient in iodine, selenium and boron.

Mulch A surface layer spread over the ground to conserve moisture and suppress weeds. Inorganic mulches include gravels, pebbles and sands. Organic mulches, such as compost, manures, lucerne, sugarcane straw, stable straw, rice hulls, peanut shells and bark products add organic matter, helping improve the soil.

Open pollinated This type of plant may also be known as an heirloom, heritage or traditional plant. Open pollinated plants are pollinated naturally in the garden by wind (such as corn) or animals (including bees). In contrast to hybrids, these plants produce seed that will grow true to type, that is, their offspring closely resemble their parents. Open pollinated plants may be more robust and less fussy than hybrids, demanding less water, food and pest control to succeed.

Organic These are fertilisers, chemicals and products that have been obtained from a source that is or has once been alive. This is also a general term used for gardening using no artificial (synthetic) fertilisers or pesticides. Products labelled organic – whether for the garden, personal or home use – should be certified by a government-registered body. See Resources section for details and logos to look for.

Permaculture A design concept developed by Australians Bill Mollison and David Holmgren in the 1970s that aims to create sustainable, intensive food production systems based on traditional methods. It also encompasses a broader social framework, promoting initiatives such as community gardens, ethical investment and city food production.

pH This is an abbreviation for the potency, or concentration, of hydrogen in soil, compost or water. It is used to measure acidity or alkalinity levels. You can test soil or compost using a kit, which gives a pH reading from 0 to 14. The pH of pure water is pH7, and this is neutral. Higher readings indicate rising alkalinity or levels of calcium in the soil. Values lower than 7 show increasing acidity. Soils in Australia are generally slightly to moderately acidic. The majority of nutrients needed for most of the plants we grow become chemically available for plant use around pH 6.5 to 7 – hence the importance of soil conditioning.

Pot on, or pot up This is when a growing plant is moved into a larger pot for more root space, allowing room for further growth. Potting on traditionally occurs in spring, allowing plants the whole growing season to respond.

Pricking out This is the technique of lifting, separating and transferring germinated seedlings from where they were sown into larger containers or a garden bed.

Seedbed A garden bed prepared for raising seeds. Preparation involves weeding, digging, firming and levelling, with rubbish, lumps of soil and rocks removed.

Slow-release fertiliser A fertiliser that releases its nutrients gradually and evenly over a period of time, such as mineral rock dusts.

Tamping Firming the soil around a plant after planting, ensuring soil supports the plant and bringing the roots into intimate contact with the soil.

Tilth A term describing topsoil, worked to become friable soil. This involves producing a crumbly, finely broken-down surface layer, such as for a seedbed.


Natural pests and diseases

Bt or Bacillus thuringiensis A bacterium that kills juvenile insects, mainly caterpillars and beetle larvae that consume it. Sprays containing Bt may be certified organic, and the concentrate readily degrades when ambient temperatures exceed 21°C.

Beneficial insect Helpful insects that work in our gardens. Some improve the soil, some cull harmful insects, and others help with pollination.

Biological pest control The practice of using animals, including insects and parasites, to destroy garden pests – for example, using Bacillus thuringiensis.

Blossom end rot A cultural problem occurring where calcium is deficient in soil. Fruit darkens and rots at blossom end. Extreme heat, inconsistent watering and root damage can exacerbate the condition. Commonly observed in tomato, eggplant and capsicum fruit.

Botanical insecticide A natural pesticide derived from plants, such as pyrethrum and neem tree, which may also be certified organic.

Companion planting Where specific plants or crops are planted together, based on the theory that this helps with pest control, nutrient uptake, pollination, or a combination of all three.

Crop rotation Growing plant members of the same crop family – such as brassicas (cabbage/broccoli) or root crops (beetroot/carrots) in separate beds, usually four to six, and avoiding planting the same group in the same bed for at least three years. This prevents the build-up of pests and diseases on continually cropped land, because each successive crop is botanically unrelated to its predecessor. Practising crop rotation is central to preventative natural pest and disease control in organic gardens.

Damping-off  This occurs where fungi attack and kill seedlings; a range of fungi may be responsible. Damage can be avoided by making sure seedlings are not overwatered, overcrowded, damaged, or grown in a poorly drained medium.

Dieback A process caused by disease, pests, drought or root damage. The effects start at the shoot tips, then move on to the branches until eventually the whole tree canopy is affected. Unchecked, the entire plant may die.

Horticultural oil Oils used in sprays to smother and suffocate pest eggs, larvae and adults attacking trees, shrubs, palms and bamboo. White oil is the traditional or old-fashioned type; it is thick and heavy compared to modern horticultural oils, such as D-C-Tron, Pest Oil and Synertrol. White oil should not be used when temperatures reach or exceed 30°C, when they may block breathing pores on leaves, resulting in burning.

IPM An abbreviation for integrated pest management, a method by which gardeners control but do not eradicate pests. IPM involves a combination of the right plants, providing good growing conditions, using appropriate organic remedies, and attracting or introducing beneficial animals into gardens or protected growing environments, such as glasshouses.

Root-bound This occurs when plants are left too long in their container. The roots begin encircling the pot and eventually lose the ability to grow normally. Girdling roots must be removed in order to restore plant vigour and achieve full growth.

Sap-sucking pests These feed on the sap in plants. Common examples include aphids, mealy bug and scale. Sap-sucking pests are farmed by ants, which actively spread them around the garden. Sap-sucking pests often exude excess sap, a sticky substance known as honeydew, which ants harvest. Unharvested honeydew coating the foliage often turns black, caused by the fungal growth of unsightly (but not injurious) sooty mould.

Solarisation a technique for destroying difficult-to-kill weeds, bulbs, and disease-affected plant debris. These materials are placed in a sealed plastic bag for several weeks to a few months, depending on the contents, and left to cook in the sun. Garden beds may also be solarised by covering them with sheets of black plastic to kill weed seeds close to the surface.