Gardening Glossary A–Z

The level of pest numbers or damage at which control is worthwhile. A few aphids can be ignored, while a colony on every shoot needs action.

Roots that grow from stems, leaves or other unusual places rather than from the main root system. Cuttings, air layers and the prop roots of banyan and maize all rely on adventitious roots.

Hanging bunches of herbs or flowers upside down in a warm, dark, airy place until crisp, to preserve them.

A way of propagating woody plants by encouraging roots to form on a branch while it is still attached to the parent. A ring of bark is removed, wrapped in moist moss or cocopeat and sealed in plastic; once roots form, the branch is cut off and potted. It is widely used for guava, lemon and hibiscus.

When root tips that reach air dry out and stop growing, causing the plant to branch into many fine roots instead of circling the pot. Fabric pots and mesh trays air-prune roots naturally.

Simple green organisms that grow in water and on damp surfaces such as pot rims, paths and pond water. Green algae on potting mix usually means it stays too wet.

A US non-profit that trials new flower and vegetable varieties across North America and marks top performers as AAS Winners.

When a plant releases chemicals that suppress the growth of nearby plants. Black walnut, sunflower and eucalyptus are known examples.

A plot of land rented, usually from a local council, for growing fruit and vegetables. Allotments are common in the UK and much of Europe.

Fertile soil deposited by rivers, found across the Indo-Gangetic plains and the Bengal delta. It varies from sandy to clayey and suits most crops.

A plant from high mountains, usually small, compact and adapted to cold, wind and sharp drainage. Alpines are grown in rock gardens, troughs and gravel beds.

When a fruit tree crops heavily one year and lightly or not at all the next. It is common in mango, litchi, apple and citrus, and can be reduced by thinning fruit and feeding well after a heavy crop.

A plant that completes its whole life cycle, from seed to flower to seed, in a single growing season and then dies. Marigolds, petunias, coriander and most vegetables are grown as annuals.

A grafting method, also called inarching, in which two rooted plants are joined side by side while both are still on their own roots, and separated once they have united. It was long used for mango in India.

A plant adapted to grow in water, either floating, submerged or rooted in mud with leaves above the surface, such as water lilies, lotus and water lettuce.

A small arched structure, called an arch or arbour in the UK, often over a gate or path and covered with roses or clematis.

A trained professional who cares for trees, including pruning, felling and diagnosing problems; called a tree surgeon in the UK.

A plant with a bold, strong shape used to create structure in a garden, such as agave, yucca, phormium, palms and tree ferns.

The small, cushion-like spot on a cactus from which spines, flowers and new shoots grow. Areoles are the feature that sets cacti apart from other spiny succulents.

A chunky, airy potting mix for monsteras, philodendrons and anthuriums, typically bark, cocopeat, perlite and charcoal in roughly equal parts.

The direction a garden or wall faces. In the Northern Hemisphere, south-facing sites are sunniest and warmest, while north-facing ones are shady and cool.

A plant hormone made in shoot tips that controls cell growth, root formation and apical dominance. Rooting powders contain synthetic auxins.

The RHS award given to plants that perform reliably in UK gardens, shown on labels as AGM. It is a useful guide when choosing varieties.

A soil bacterium that produces proteins toxic to caterpillars when eaten, but harmless to people, pets, bees and most other insects. It is widely used against leaf-eating caterpillars.

The protective outer layer of the trunk and branches of woody plants. Damage to the bark, from tools, ties or animals, opens the way for pests and disease.

A cutting taken from new shoots at the base of a plant in spring, used for dahlias, delphiniums, chrysanthemums and lupins.

A naturally occurring fungus that infects and kills many insects, including whiteflies, thrips, aphids and beetles. It is sold as a biological insecticide.

A plant grown for a season of colour, usually an annual such as petunia, marigold or begonia, planted out in beds, pots and baskets.

A shelter of hollow stems or drilled wood for solitary bees to nest in. Place it facing the morning sun, about a metre off the ground.

A container sunk into the soil and filled with beer, which attracts slugs and snails that fall in. Leave the rim slightly above the soil so ground beetles do not drown.

Microscopic worms sold as a biological control that hunt soil pests such as vine weevil grubs, fungus gnat larvae, cutworms and chafer grubs. They are watered onto moist soil.

In botany, a fleshy fruit with seeds inside and no stone, such as tomato, grape, guava, banana and chilli. Strawberries and raspberries are not true berries.

The variety of living things in an area. A garden with many kinds of plants, habitats and water supports more beneficial insects, birds and soil life.

A pest control product based on living organisms or natural substances, such as Bacillus thuringiensis, Beauveria bassiana, Trichoderma or neem.

Lightweight netting draped over fruit bushes and crops to keep birds from eating berries and seedlings. Check it daily so birds do not become trapped.

Heavy, clay-rich soil, also called regur or cotton soil, found across the Deccan plateau. It holds moisture well and is fertile, but swells when wet and cracks when dry.

A plant that grows in permanently wet, waterlogged soil at the edges of ponds and streams, such as taro, papyrus, iris and pitcher plants.

The scientific Latin name of a plant, made of its genus and species, such as Azadirachta indica for neem. It identifies a plant precisely when common names vary from place to place.

Gentle warmth applied beneath seed trays or cuttings, usually from a heat mat, to speed germination and rooting.

The moment in spring when buds open and new leaves or flowers begin to emerge. Many sprays and pruning tasks are timed by bud break.

Planting several kinds of bulbs in layers in one pot, with the largest and latest-flowering deepest and smaller, earlier ones on top, for a long succession of spring flowers.

A small bulb-like bud that forms in a leaf axil or flower head and can grow into a new plant. Garlic, some lilies, yams and agaves produce bulbils.

A decorative outer pot without drainage holes that holds a plain plastic nursery pot. Empty any water that collects in it after watering.

A fast-draining potting mix for cacti and succulents, usually potting soil with plenty of grit, coarse sand, pumice or perlite.

The ring of sepals at the base of a flower, which protects the bud before it opens. In roselle, the fleshy red calyx is the part that is eaten.

The capture and long-term storage of carbon dioxide from the air in plants and soil. Trees, hedges, perennial plantings and soil organic matter all store carbon.

The balance of carbon-rich and nitrogen-rich materials in compost. A ratio of about 25–30 parts carbon to 1 part nitrogen breaks down fastest without smelling.

A plant that traps and digests insects to obtain nutrients in poor, boggy soils, such as Venus flytraps, pitcher plants and sundews. They need pure water and no fertilizer.

A tomato disorder that causes scarred, puckered and misshapen fruit, often after cold weather during flowering. Affected fruit is still edible.

A measure of how well soil holds on to positively charged nutrients such as calcium, magnesium and potassium. Clay and organic matter give soil a high capacity; sandy soils have a low one.

Produce, seed or products verified by an approved body (such as USDA Organic in the US or the Soil Association in the UK) as grown without synthetic pesticides and fertilizers.

Cutting back late-flowering perennials such as sedum, phlox and asters by a third to a half in late spring, which makes them bushier and delays flowering.

A plant made of two or more genetically different tissues, which often causes variegation in stripes or patches, as in some pothos and monstera varieties.

Letting seed potatoes sprout short, sturdy shoots in a cool, bright place for a few weeks before planting, which gives an earlier crop.

A tiny structure inside plant cells that contains chlorophyll and carries out photosynthesis.

Yellowing of leaves caused by a lack of chlorophyll. Yellowing between green veins on new leaves often points to iron or manganese deficiency, while older leaves yellowing first suggests a nitrogen or magnesium shortage. Poor drainage and the wrong soil pH are common causes.

Cutting back a leggy houseplant and rooting the cuttings, then replanting them in the same pot to make it fuller.

Fruit that keeps ripening after picking, such as banana, mango, tomato, avocado and pear. Non-climacteric fruit, such as citrus, grapes and strawberries, does not get sweeter once picked.

A small, portable cover of glass or plastic placed over individual plants or rows to protect them from cold, wind and pests.

A plant that is genetically identical to its parent, produced by cuttings, grafting, layering, division or tissue culture. Named fruit varieties and many flowers are kept true as clones.

A lawn sown with clover, alone or mixed with grass. Clover stays green in drought, fixes nitrogen, needs little mowing and feeds bees.

A fibrous growing medium made from coconut husks. It holds water well, stays airy and is a renewable alternative to peat. It contains few nutrients, so it is mixed with compost and soil, and should be rinsed before use if it is salty.

Adding materials to a compost heap or bin gradually and leaving them to rot slowly over many months with little turning. It is easy but does not kill weed seeds.

The everyday name of a plant, which can differ by language and region. Tulsi, holy basil and Ocimum tenuiflorum all refer to the same plant.

A shared garden tended by a group of people, often in towns and cities, where members grow food and flowers together.

Growing different plants close together so they benefit each other, for example marigolds among tomatoes to attract pollinators and predatory insects, or basil beside chillies. It also makes better use of small spaces.

Decomposed plant and kitchen waste that has broken down into a dark, crumbly material. It improves soil structure, holds moisture and feeds plants slowly.

A nitrogen-rich material, such as grass clippings, manure or a bagged product, added to a compost heap to speed up decomposition.

A container for making compost from garden and kitchen waste. Slatted wooden bays, plastic "dalek" bins and rotating tumblers are common types.

A leaf divided into several separate leaflets on one stalk, as in neem, rose, curry leaf and moringa.

A cone-bearing tree or shrub, usually evergreen with needle- or scale-like leaves, such as pines, firs, cedars, junipers and cypresses.

Plants sold growing in pots, which can be planted at almost any time of year as long as the ground is not frozen or waterlogged.

A vegetable that grows best in mild temperatures, roughly 10–24 °C, and may bolt or turn bitter in heat, such as lettuce, peas, spinach, cabbage and carrots.

Lawn grasses that grow best in spring and fall in cool climates, such as Kentucky bluegrass, perennial ryegrass and fescues. Common in the northern US and the UK.

A US network of university-based offices that provide free, research-based gardening advice, soil testing and plant problem diagnosis in every state.

Adhesive copper strips placed around pots and raised beds to deter slugs and snails, which avoid crossing copper.

A fruit tree or bush trained as a single stem, usually at an angle against wires, with short fruiting spurs. Cordons let you grow many varieties in a small space.

Removing small plugs of soil from a lawn to relieve compaction and let air, water and fertilizer reach the roots, best done in fall for cool-season grass.

A swollen, solid underground stem base that stores food, covered by papery scales. Gladiolus, crocus, taro and elephant foot yam grow from corms.

All the petals of a flower together. The corolla attracts pollinators with its colour, shape and scent.

An informal garden style with densely planted flowers, herbs and vegetables mixed together, often with self-seeding plants such as foxgloves, hollyhocks and poppies.

The stems, leaves and roots left after harvest. Healthy residue can be composted or dug in to add organic matter; diseased residue should be removed.

Drying or hardening harvested crops so they store well, such as drying onions and garlic in the sun, or keeping sweet potatoes and squash warm for a week to toughen their skins.

A garden or bed planted mainly to grow flowers for cutting, such as zinnias, dahlias, cosmos, sweet peas and snapdragons.

A way of harvesting leafy crops by cutting outer leaves or shearing the plant above the growing point, so it regrows for several more harvests.

A piece of stem, leaf or root removed from a plant and encouraged to grow roots of its own. Stem cuttings are usually taken just below a node and placed in water, moist soil or sand.

A plant hormone that promotes cell division and side-shoot growth and delays ageing of leaves. It works with auxin to control branching.

The number shown on seed packets estimating how long a variety takes from sowing or transplanting to first harvest.

A boundary or habitat made by stacking prunings and branches between posts. It recycles garden waste and shelters insects, birds and small mammals.

Removing faded or spent flowers from a plant. It keeps the plant tidy and encourages many flowering plants to produce more blooms instead of setting seed.

A hydroponic system in which plant roots hang in an aerated nutrient solution, kept oxygenated by an air pump.

Describes plants that deer usually avoid, often because they are aromatic, hairy, spiny or poisonous, such as lavender, daffodils, foxgloves and hellebores. No plant is completely deer-proof.

Describes tomato and other plants that grow to a fixed bushy height, set most of their fruit at once, and then stop. They need little pruning and suit containers.

Removing the thick layer of dead stems from a lawn with a rake or machine, usually in spring or fall, so water and air can reach the roots.

A fine powder made from fossilised algae that damages the outer coating of crawling insects and slugs. It only works while dry and also harms beneficial insects, so use it sparingly.

Splitting a clump-forming plant into several smaller plants, each with its own roots and shoots. It is the easiest way to propagate snake plants, peace lilies and many grasses, and is best done when repotting.

A bud that stays inactive until triggered by pruning, damage or the right season. Hard pruning wakes dormant buds on old wood in many shrubs.

Pruning deciduous trees and shrubs in winter while they are leafless, when their structure is easy to see. It encourages vigorous regrowth in spring.

A deep cultivation method in which soil is loosened to two spade depths and enriched with organic matter. It improves drainage and root depth in compacted ground.

How quickly excess water moves away from plant roots. Good drainage depends on a loose soil mix and pots with drainage holes. Poor drainage leaves roots short of air and leads to root rot.