What are annual, biennial and perennial plants?

Starting out in gardening? Don’t be bamboozled by confusing terminology, Martyn Cox unravels the difference between many types of plants.

Plant terms made simple

Thousands of Brits took up gardening for the first time during the coronavirus lockdown but navigating your way through a multitude of plant terms can be tricky for beginner gardeners. Whether you’re baffled by biennials or confused by corms, don’t feel daunted. Here’s my guide to some of the most common plant terms you’re likely to come across.

Annuals

Annual plants are those that complete their life cycle within a single growing season. They will germinate, produce leaves and flower before all parts die, including the underground roots, leaving only the seeds to survive from one season to the next. We grow lots of annuals in the garden, from nasturtiums to lettuces, and from love-in-a-mist to peas.

Biennials

These are plants that flower and set seed in their second season after germination. Typically, they will form a cluster of leaves during their first growing season and flower the next before setting seeds and dying back. Well-known examples include wallflowers, sweet Williams, Echium pininana, kale and some foxgloves. 

Perennials

Plants that live for more than two years are known as perennials. Some persist for decades or longer, while others have a shorter life span. Technically, the term applies to trees, shrubs and other long-lived plants, but is usually used to describe non-woody plants that are grown in beds and borders, such as delphiniums, lupins and bergenia. Herbaceous perennials are plants with foliage that dies back to ground level each autumn, such as hostas and many red-hot pokers.

Shrubs

Shrubs are woody-stemmed plants with multiple permanent branches that form at or close to ground level. They come in many shapes and sizes, from prostrate, ground-covering species to large, rounded specimens. As a rule, shrubs grow to no more than 5-6m (15-20ft) in height, but most are considerably smaller. There are both evergreen and deciduous types.

Trees

These are perennial plants that form a permanent, woody trunk that supports a head of branches. There are evergreen, semi-evergreen (ones that lose their leaves in a cold winter) and deciduous types in a bewildering range of shapes and sizes. A standard tree is one with a 2m (6½ft) clear stem before the branches start, while a half-standard has about 1m (3ft) of clear stem beneath the branches.

Conifers

A massive group of trees and shrubs that often have needle-like leaves. There are both evergreen and deciduous species, with many that have seeds contained within cones. Among well-known members are pines, spruces, yews, cedars and monkey puzzle trees. 

Bedding plants

Bedding plant is the umbrella title given to a huge range of tender annuals and perennials. Marigolds, petunias, New Guinea impatiens and many other types are raised in heated greenhouses and then planted out after the last frosts, typically late spring or early summer. The term ‘bedding’ comes from the tradition of planting these fast-growing plants in outdoor beds to create seasonal displays. Although some popular species are perennials, bedding plants are generally discarded at the end of the growing season. 

Climbers and wall shrubs

Climbing plants produce long stems that have an inclination to go upwards. Some require regular tying to supports, while others are self-supporting, using tendrils, adhesive pads or aerial roots (little roots that form on stems) to anchor themselves. Wall shrubs don’t naturally climb but with pruning and training, they can be grown against upright supports.

Bulbs, corms, tubers, rhizomes

All of these are fleshy, dormant food storage organs that require planting underground. True bulbs are composed of several layers of fleshy ‘scales’ that surround the undeveloped leaves and flower bud, while the other structures are actually swollen stems. There are distinct differences between them all but for simplicity’s sake many gardeners refer to the lot as bulbs.

Alpines

These are tough, compact plants that tend to grow in mountainous regions in nature, although the term loosely covers any low-growing plants that are suitable for growing in rock gardens. Most alpines are perennials, but there are also shrubs, bulbs, ferns and succulent plants, such as houseleeks and sedums. 

F1 hybrids

Many annuals, perennials and vegetables that are grown from seeds will have the words F1 hybrid printed on their packets. These varieties have been bred for uniformity, health, vigour and in the case of vegetables, high yields. On the downside, there’s little point collecting seeds from these plants in your own garden because they will not produce plants that are identical to their parents.