Great Blooming Gardens

Get your garden blooming bright!

Get to know the different plant categories 

For most people flowers are the crowning glory of our garden, the enthralling and thrilling reward for all our efforts. Much is the pity for beginners who often feel confused by the vast diversity of the plants from which they have to choose.  However, the confusion can be reduced a great deal if we divide flowers into their broad botanical categories.  The flowers within each category share common characteristics, so the category to which a flower belongs will determine how, where and when it should be grown.

Plants are allotted to convenient categories according to their hardiness and the following descriptions will help you to understand these classifications.  All plants exhibit varying degrees of hardiness, or tolerance towards cold and damp, and this tolerance is directly related to the climates of their countries of origin.

We will explain the differences between annuals, biennials, herbaceous plants, trees, shrubs and climbers and divide the confusing bulb group into bulbs, corms, rhizomes and tubers.

A lot of the terms used to describe plant categories are usually abbreviated in catalogues and plant references, and we have given these initials following the full name, where appropriate. 

We hope this is helpful and in future editions we will explore each category in greater depth. 

Annuals A, Hardy Annuals HA, Half-Hardy  HHA

These are plants that grow, flower and die in a single season.  Hardy annuals are capable of withstanding frost and are generally sown outdoors in the place where they are intended to flower.  Half-hardy annuals of which many are sold as bedding plants, are raised in warmth and not moved outdoors until the danger of frost is over. 

Biennials   B

These are plants that flower and die the year after they have been sown.  Foxgloves (Digitalis), for example, are sown in early summer, planted out during the autumn and flower the following spring.  Usually they die after their seeds have formed.

However, the accuracy of the term ‘biennial’ depends to some extent on how the plants are grown.  Some biennials will flower in the first year if raised under glass in the same way as half-hardy annuals. 

Herbaceous Perennials   HP

Plants that live for a number of years, their growth dying down each autumn, are called herbaceous perennials.  They are also termed ‘hardy’ plants, as they can withstand severe winters in their dormant state.  Some hardy types can go through the winter without losing their stems or foliage. 

Bulbs and corms

Botanically speaking, bulbs are underground buds and corms are underground stems.  These flowering plants, many of which may be left undisturbed for many years , come in many different varieties.  They are by no means confined to spring flowering.  There are species to bloom in summer, autumn and even winter. 

Tubers

Certain plants, including dahlias and some begonias, have fleshy underground stems or roots which carry buds for the following year’s growth.  Called tubers, they have been singled out here, not because they demand a particular site or growing conditions, but because their care and propagation differs a little from other plants. Tuberous plants use their swollen roots to store nourishment during the winter and ensure a good start the following spring. 

Rhizomes

A rhizome is a fleshy underground or creeping, root-like food storage organ from which leaves, stems and flowers grow upwards and roots downwards.  It tends to be scaly and look ‘jointed’.  Typical examples are flag irises, lily of the valley (Convallaria) and Solomon’s Seal (Polygonatum), which are all hardy plants. 

Climbers

Most garden climbing plants are shrubs, but there are also some other types worth considering.  In particular, plants such as the nasturtium (climbing varieties), will cover a fence or an arch very rapidly and provide a mass of colour during the summer months.  Some climbers such as Morning Glory (Ipomoea) are half-hardy and need to be raised in a greenhouse before being planted out once there is no risk of frost. 

Rock plants

These are often called alpines because originally they came from hilly or mountainous regions.  Rock plants consist of some of the most intense and daintiest of all garden plants.  You will find perennial rock plants, both evergreen and deciduous as well as some shrubby types.  Most rock plants are perfectly hardy but tend to dislike damp conditions.  You can protect your alpines from winter damp by use of small glass or plastic cover.  If you do not have a suitable site for a rock garden they will grow just a happily in a well-drained trough or raised bed.   

Trees

These are usually defined as perennial plants that are woody, with one main stem (trunk), and a mass of branches and stems above and usually grow over 4m (13 ft) tall.  They are generally sub-divided into two categories: the broad-leaved kinds which can have a variety of different shaped leaves showing a network of veins and the conifers, which have needle-like or ‘scale’ leaves.

Trees can take many years to mature.  They can also be either, hardy, half hardy or tender. Trees and shrubs are often referred to as “evergreen” meaning they retain their leaves in winter or “deciduous” when they shed their leaves in autumn and produce new ones in the following spring. 

Shrubs

Unlike trees, these are woody perennials that branch naturally from the base and have more than one main stem.  They can grow as tall as 8m (26 ft) or be only a few centimetres (1-2 ins) high.  Like trees, they can be hardy, half-hardy, or tender.  It is prudent to plant only the hardy kinds outdoors in Britain unless you have a very sheltered site.  Shrubs are sometimes called bushes, and this term can also refer to a cluster of shrubs.