Acid soil
Acid soils have pH readings of less than about pH6.5. Acid conditions are preferred by lime-hating (ericaceous or calcifuge) plants. Acid soils are sometimes the result of poor drainage and may be corrected by cultivation and the addition of lime.

Small, compact and generally non-invasive perennials, suitable for growing in rock gardens, troughs, scree beds and similar limited spaces.

Annual plant
A plant that normally completes its full cycle of growth, flowering and seeding in a single season, and then dies. Some annuals may be sown in autumn to flower the following spring.

Alkaline soil
Alkaline soils have pH readings above pH7.4 and contain relatively more lime. Alkaline soil suits lime-loving (calcicole) plants such as many alpines and many vegetables, especially brassicas (cabbage family). Alkaline soils are harder to make more acid, although the addition of leafmould and sulphate of iron can lower the soil’s pH value.

Minute plant-feeding insects within the super family Aphidoidea. Commonly known as greenfly, blackfly or plant lice.

Bedding plants
Any plant that’s planted out in a bed, border or pot for a seasonal display, usually during spring and summer. The plants are then removed, making way for next season’s display. Spring bedding is composed of spring-flowering bulbs, hardy perennials and biennials. Summer bedding plants include hardy and half-hardy annuals, tender perennials and summer-flowering bulbs.

A plant that takes two years to complete its life cycle. It produces leafy growth in its first year and then flowers and sets seed during the following season before dying.

Bog garden
An area that is often linked to a pond, where marsh and other moisture-loving bog plants can be grown. A punctured buried liner will keep the soil permanently damp, but it will also prevent it from becoming too waterlogged.

Bog plant
A pond side plant, such as the giant rhubarb, Gunnera manicata, or cotton grass, Eriophorum angustifolium, that needs very moist but not waterlogged soil. Many grow naturally in marshes. A collection of bog plants is typically called a bog garden.

A reduced or modified leaf, from the axil of which a flower or flower stalk grows.

A short, underground stem with fleshy, modified leaves, used as a food storage organ by a dormant plant.

This can mean garden compost made from waste materials rotted down in a compost heap, but it usually refers to the special soil or peat mixtures used for sowing and potting plants.

There are two main kinds. Soil-less compost is made from peat or a substitute such as bark or coir. Soil-based composts are a mixture of sterilised soil, peat or an alternative, and sand. They all have added fertilizers.

A universal, soil-less compost is suitable for all normal sowing and potting needs, but there are different grades of soil-based compost. You can also buy special composts for rooting cuttings or for growing ericaceous (lime-hating) plants, orchids, and water plants.

Make sure the compost you use is moist, warmed to room temperature, and fresh. Don’t keep left-over compost from one season to the next as the fertilizers sometimes change into harmful chemicals with age. Instead, use up your old supply to improve the soil outdoors.

Perennial trees or shrubs that produce insignificant flowers followed by seed-bearing cones. Almost all are evergreen foliage plants, ranging in size from tall giants to miniature rock garden shrubs.

An underground storage organ comprising a short, swollen portion of stem protected by a layer of skin known as a tunic. Corms are planted like bulbs.

Broken pieces of clay pot, which are used to cover the holes in the bottom of pots. The crocks help to stop compost blocking the holes and improve drainage. Stones, coarse gravel or large fragments of polystyrene are useful alternatives.

The upper part of the roots of a perennial, such as rhubarb, peonies or asparagus.

A plant that has evolved in cultivation and which is sufficiently different from all others to receive a unique cultivar name. Cultivar names are printed with a capital letter and in single quotation marks, e.g. ‘Alba’ is the cultivar name in Veronica longifolia ‘Alba’. The abbreviation for cultivar is cv. In everyday parlance, cultivars are often called varieties.

A portion of root, stem or leaf cut from a plant and made to produce its own roots so that it becomes a new plant exactly like its parent.

Removing flowers as they fade to prevent the plant from wasting valuable energy on forming seeds and to keep plants looking tidy. Deadheading extends the life of annual plant flowers and can prolong the flowering of perennials, especially roses.

Deciduous trees and shrubs shed all their leaves in autumn and early winter. Plants lose a lot of water through their leaves, especially in windy weather, and this can be lethal in winter, so deciduous plants protect themselves by dropping their leaves and resting dormant until growth starts again in spring.

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

At rest, usually used to describe deciduous or herbaceous plants in winter when growth is not active, and seeds before they germinate.

Evergreens keep their leaves all year and continue growing slowly in winter. The leaves are protected from frost by their thick, often waxy skin. Some of the older leaves are shed through the year. A few plants such as privet are semi-evergreen, normally keeping their leaves except in cold winters. The leaves of young evergreens can be damaged by cold wind, so give them shelter in exposed gardens.

Any substance, organic or inorganic, used to increase soil nutrients. It can be straight, containing only one nutrient, such as nitrogen; or compound, containing more than one nutrient; or balanced, containing equal quantities of plant nutrients.

To be flower bearing. It is sometimes misused to describe an abundance of flowers.

The leaf of a palm or fern, usually having many divisions.

Frost pocket
A small, low-lying area, where late and early frosts are more likely, increasing the risk to tender plants.

Half hardy
Applied to annuals, this indicates that a plant is able to cope with temperatures down to 0°C (32°F) but not hard frost.

Half standard
Refers to trees whose trunks are unbranched up to 3-4ft from ground level. Also applies to plants having significantly shorter stems than standard forms.

Hardening off
Hardening off involves acclimatising plants to outdoor temperatures so they can survive outside without being damaged by frost or cold. Plants raised indoors in warmth are soft and likely to suffer if you suddenly expose them to the elements. But you can avoid this by gradually acclimatising them to lower temperatures for a week or two beforehand.
This can be done by standing the plants in a sheltered place outside on mild days, just for a few hours at first but slowly lengthening the time until they’re eventually left outdoors all day and night. Alternatively, you can move them to a cold frame. Keep the lid closed to start with, and then admit a little air, increasing this daily until the frame is left wide open all the time, after which the plants should be ready to plant out.

This is an indication of a plant’s ability to withstand low temperatures, although it is not an absolute measure and may be affected by factors such as shelter and drainage.

Hardwood cuttings
Describes cuttings prepared from the woody mature stems of trees and shrubs, usually in autumn and winter.

Hardy perennial
A herbaceous perennial plant able to withstand exposure to sub-zero temperatures.

Heavy soil
Heavy soils contain more clay and are sticky and hard to work but tend to be more fertile. They often remain cold and wet in spring and need grit or coarse organic material to admit air and help roots remain healthy.

Soft-stemmed, not woody. Usually used to describe perennials that die down and become dormant in winter.

The flowering part of a plant, or mode of flowering. Inflorescences may be of many kinds: spike, panicle, umbel, capitulum, corymb, cyme and spadix.

John Innes
The John Innes Horticultural Institute was founded in 1904, ‘for the improvement of horticulture by experiment and research’. It was set up with money bequeathed by a London businessman of Scottish descent. John Innes composts were developed as an attempt to standardise compost formulae at a time when nurserymen were bringing a confusion of formulae to the market. The range includes John Innes seed compost, for seed sowing or rooting cuttings; John Innes potting compost No.1 for initial potting; John Innes potting compost No.2 for potting on; and John Innes compost No.3 for final potting of stock plants. Composts like this, which are soil based, should be stored in dry conditions and used within a month of purchase.

Light soil
Light soils are sandy or silty with very little clay. They are generally easy to work, warm up quickly in spring, dry out rapidly and benefit from added organic material to help keep them moist and fertile.

The washing out, usually by rain, of soluble (and some insoluble) minerals from the soil. Because some substances leach faster than others, this may cause a chemical imbalance in the soil, which, in turn, may have a detrimental effect on plants. Commonly a problem with pot plants.

Leaf mould
Composted fallen leaves, or the detritus of partially decayed leaves found under trees.

Leaf spot
Symptom of a variety of viral diseases that attack the leaves of many plants, but particularly roses. The spots can be of various colours. Afflicted plants will need to be treated with a fungicide.

Rich, fertile soil, with a balance of sand, clay and humus.

Marginal plant
A water plant that grows at the edge of the pond or on the bank where its roots can reach shallow water. There are many kinds, including water mint, Mentha aquatica, and flowering rush, Butomus umbellatus.

A surface layer spread over the ground to conserve moisture, suppress weeds and maintain a good soil texture. Mulches may be organic, such as manure, compost, bark chips or cocoa shells, or non-organic, for example, stones, gravel or polythene sheeting.

A chemical element with the symbol N. Nitrogen is a macronutrient, that – along with oxygen, carbon and hydrogen – is essential for plant growth.

The point on a stem from which a leaf or leaves arise.

Organic gardening
The cultivation of plants without the use of chemicals of inorganic origin.

An influorescence having several branches that are either opposite or alternate. A loose cluster of flower heads blooming from the base upwards.

The accumulation of partially decayed and carbonised vegetable matter. Deposits form in peatlands or wetlands, known variously as bogs, moors, mires and muskegs, and are used as fertilizer.

Any plant with an indefinite life span of more than two years. Some may be quite short-lived, whereas trees can easily survive for centuries.

This abbreviation is short for the potency, or concentration, of hydrogen. It is used to measure the acidity or alkalinity of soil, compost or water.
You can test the soil with a with a simple kit, which gives a pH reading from 0 to 14. A value of pH 7.0, that of pure water, is neutral. Higher readings indicate higher alkalinity, or levels of lime. Values lower than 7.0 show increasing acidity.

Garden soil usually ranges from pH 4.5 to pH 8.0. Few plants will grow well at more extreme values. Most prefer soil that is between pH 6.5 and 7.0, but ericaceous plants like soil that is ideally below pH 6.0.

The second component of NPK. Phosphates may be sold as rock phosphate, super phosphate or triple super phosphate. Occurs naturally in banana skins, bone meal and dried blood.

A non-metallic chemical element having the symbol P. Phosphorus is found in all animal and vegetable organisms, and is an essential plant nutrient, encouraging healthy root development. The P in NPK formulae.

Pinching out
The method of stopping a plant growing upwards by removing the growing tip, thereby encouraging the development of side shoots.

The practice of pruning tree branches back to the trunk to encourage the production of young shoots and foliage. Often used in the development of ornamental trees.

Pot on
When a growing plant is moved into a larger pot for more root space.

Pot ready
This is a young, well-established plant. It is sometimes sold bare-rooted but is usually in its own individual paper pot or Jiffy_7. It is ready for you to grow on in a 9-10cm (31/2-4in) pot or you can plant it directly into a hanging basket.

The term propagation defines the various methods by which the numbers of a plant are increased. There are several different methods, each of which depends on the plant that you are going to increase. Some of these are simple enough to carry out even by the most inexperienced gardener, while some require skills of a seasoned professional. The two most basic methods used are layering and cutting.

An inflorescence on which individual flowers, on short stalks of their own, arise from a central, unbranched stem. Normally these flowers open from the base upward.

A swollen underground stem that is able to continue extending, unlike a tuber. Rhizomes are used as storage organs by dormant plants.

The matted roots and soil of a plant that can be seen when transplanting a pot plant, and which should be kept entire.

Describes a cluster of leaves arranged in a tight circle, usually close to the soil surface, as seen on a dandelion. The term may also be used to describe the corolla of a flower.

A fungal disease that causes rust-coloured spots on leaves, stems and other parts of a plant.

A stem that extends sideways above or just below ground, with new plants and roots produced at intervals along its length.

Scale insect
Small, sap-sucking insects.

Specimen plant
Any well-grown plant placed on its own in a prominent position where it can develop fully and be admired as a solo performer.

A plant or shrub pruned and trained to grow into a tree-like form, with one trunk or stem that’s 3-6ft long before branches appear. The practice is entirely aesthetic, and often used for roses. (See half standard.)

A shoot which runs along or just below the ground which roots at the tip and produces a new plant. Differs from a runner which produces roots at the nodes along the length of the stem.

An extra stem growing direct from the roots, usually best removed from grafted plants.

This is the layer below the top soil which is usually less fertile and of poorer texture.

The subsoil usually looks pale because of its low fertility. It is sometimes hard and compacted and stops water draining away, creating waterlogged conditions that slow down plant growth or cause root diseases. Subsoil often contains valuable minerals that can be tapped by growing deep-rooting plants such as alfalfa or fenugreek and adding them to the compost heap. They help to break up the subsoil, as does deep digging. Because of its poor quality, never leave subsoil on the surface.

Tap root
The large, central root that grows downwards, and from which smaller, lateral roots grow.

These plants, often perennials from warmer climes, are sensitive to cold and frost and must be kept above 5°C (41°F).

The tip or apex of a plant.

Thinning out
The practice of reducing the number of plants in a bed or container to provide more room for growth. In fruit production, to reduce the crop of fruitlets early on in order to produce larger fruits for harvest.

This is the top layer of soil. It is usually the most fertile, being dark in colour and crumbly.

If you dig into undisturbed garden soil, you’ll find it has a clear structure. The upper layer or topsoil, which can vary widely in depth, is normally dark, a sign that it is rich and full of plant foods. Garden plants grow best in topsoil that is well broken up, fertile and able to hold moisture. Regular cultivation aims to maintain and improve these qualities. After a number of years, very high quality topsoil can be produced. Keen gardeners have been known to take it with them when moving house.

A swollen root that provides stored food for dormant plants. Tubers often possess buds or eyes from which new plants can grow.

To add one or more complementary, low-growing plants beneath and around taller plants.

Refers to foliage having patches of different colours, usually as a result of the chlorophyll content. Common combinations are green with cream, white or silver, although some plants produce foliage that mix green with reds and yellows.

A variety is a plant that has evolved in the wild from a species or subspecies and which is sufficiently distinct to be given its own varietal name after the abbreviation var. For example, Acer palmatum var. dissectum has more finely cut leaves than Acer palmatum. In everyday usage, variety is often used where cultivar is really meant.

Water plants
Plants that live in water, in ponds or waterlogged areas. Water plants are usually divided into different groups, according to the depth of water they like or what they do.

A member of the beetle family Curculionidae. Weevils are small in size, with an elongated head, and can cause serious damage to fruits, nuts, trees, etc.

Well-drained soil
Well-drained soils – typically light soils but also those which are well-cultivated and not waterlogged. Suit most plants because surplus water drains away rapidly, avoiding the risk of disease and providing the aeration needed by most roots (digging, adding coarse materials such as grit or creating raised beds can all improve poorly drained soil).

Wet soil
Wet soils, usually heavy or peaty in nature, hold water well and dry out slowly. They are suitable for many marginal or moisture-loving species, and also some aquatics, but need improved drainage for other species to survive healthily.

Plants able to withstand extreme drought conditions, eg, cacti.

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