What is the difference between annuals and perennials?

annuals and perennials - what is the difference?

The difference between perennials and annuals is one of the questions about plants that can be confusing, especially if you are new to gardening. Here we consider annuals and perennials, highlighting how they differ and clearing up whether some of our most popular plants are annuals or perennials.

Perennial vs annuals: the key difference

The key difference between perennials and annuals is the time it takes for them to complete their life-cycles. Technically, a perennial is a plant that can live longer than 2 years. An annual, on the other hand, completes its life-cycle, from seed to flower to seed again, in one year. Annuals appeal to gardeners because a lot of them are showy plants that flower for long periods during the summer, but perennials have the great advantage of coming back year after year.

Typical perennials that we grow in our gardens include dahlias, geraniums, thalictrums, and rudbeckia. Typical garden annuals include nigella, calendula, and papaver (poppies).

Annuals vs perennials - NIgella
Annual Nigella damascena – Love-in-a-mist

What Are Annuals?

Annual plants germinate from seed, grow and mature, flower and set seed all within a year. In fact they usually do all of that within the growing season, which is some places can be no more than a few months.

Ultimately, the goal of all plants (indeed all living things) is to reproduce, in order to pass on their genetic profile to another generation.

For annual plants, this means setting seed – and to do that they have to flower. This propensity to flower, and in many cases, to flower profusely, is why, as gardeners, we take the trouble to grow annuals from seeds each year.

We can prolong flowering by deadheading our annuals. This mean removing the spent flowers before the plants set seed. By doing this the plant is stimulated to produce more flowers in its quest to produce its seeds.

Annuals can therefore flower for long periods with the right care. As I write this it is the end of October and I can look out into my garden and see annual petunias, and nasturtiums still flowering. These were tiny seedlings in April – and this is Scotland, not known for its extensive growing season.

There are two main types of annuals – half hardy annuals and hardy annuals.

hardy annual Nasturtium
Hardy annual: Tropaeolum majus (nasturtiums)

Half-hardy Annuals

Half-hardy annuals are tender plants and cannot withstand frost. But they are also unable to grow well in cold temperatures (below 5°C). You therefore need sow half-hardy annuals in frost free environments and should not plant them out until the last frost has passed. They’ll perform during the summer but will be killed by the first frosts of autumn.

Examples of half-hardy annuals are: Tagetes patula (french marigolds), Nicotiana affinis (tobacco plant) and Cosmos bipinnatus (cosmos).

Annual Tagetes - french marigold
Half-hardy Annual: Tagetes patula (french marigolds)

Hardy Annuals

Hardy annuals can tolerate cold and frost, so you can sow them outdoors in early Spring. They will germinate as soon as the soils is warm enough. Some, such as sweet peas and forget-me-nots, can be sown in autumn and will germinate and spend winter as small plants.

Examples of hardy annuals include Helianthus annus (Sunflowers), Tropaeolum majus (nasturtiums), Nigella Damascena (love-in-a-mist) and Lathyrus odoratus (sweet pea).

hardy annual - Sweet pea
Hardy annual: Lathyrus odoratus (sweet pea)

Biennials

There are some plants which complete their life cycle in a period of 2 years. These are called biennials. In the summer of the year they are sown they and typically grow a rosette of leaves. They will then flower in the following year, set seed to start the process over again, and then die off. Dianthus barbatus (sweet Williams) and foxgloves (Digitalis purpurea) fall into this category.

Some plants we think of as biennials (and sweet Williams fall into this category) are technically short lived perennials, but as gardeners we treat them as biennials because they do not perform so well after they have flowered for the first time.

Biennial - sweet William
Sweet William (Dianthus) – often treated as a biennial

Ephemerals

There are even some plants, for example groundsel (Senecio vulgaris) that complete more than once life-cycle in a single year. These are called ephemerals.

What are perennial plants?

Although a perennial is a plant that can live for at least 2 years, most perennials live for much longer that that.

Trees and shrubs fall into the 2 year plus category, and these usually categorised as woody perennials. Sometimes bulbs are excluded from the perennial category, but a lot of bulbs will return year on year, so I generally think of them as perennial plants.

Just like annuals, perennial plants can reproduce by setting seed, but they can also reproduce vegetatively.

Typically this is done by their roots (particularly specialised types of roots like rhizomes and stolons) spreading underground. It means that the plant can extend itself out into the soil around it and survive if parts of the original plant are removed or damaged.

As gardeners we take advantage of these means of vegetative reproduction, for example by dividing perennials of taking root cuttings, as a way to increase our stocks of desirable plants.

Herbaceous perennials

Herbaceous perennials die down in autumn and lie dormant as a ‘root stock’ over winter. They then re-grow in Spring. In fact, one of the great joys of gardening is the sight of my herbaceous perennials breaking the surface with their new green shoots in march or April. This, for me, is the first sign of summer to come. Typical herbaceous perennials are delphiniums, lupins and sedums.

hardy perennial - Delphinium
Delphiniums – herbaceous (and hardy) perennials

Evergreen perennials

Evergreen perennials thrive from year to year but their foliage does not die down over the winter period. Examples include hellebores, heuchera, iris or bergena. The look of evergreen perennials is improved by trimming off the old and damaged leaves in Spring.

Heuchera - evergreen perennial
Evergreen perennial – Heuchera

Hardy perennials

For those of us who garden in frost prone regions, most of the plants that we think of as perennials are hardy perennials. They can be left in the garden all year round and only lifted if we want to move or divide them.

Tender perennials

These are the plants that can live on year after year, but only if they are not exposed to frost. Many types of fuschia, pelargoniums, and cannas fall into this category.

FAQs

1.   Are geraniums annuals or perennials?

Hardy geraniums, for example Geranium Johnson’s Blue are perennials. Pelargoniums, which people often refer to as geraniums are perennials in warm climates, but are generally grown as annuals in frost prone areas.

2.   Are begonia annuals or perennials?

There is a huge number of species of begonia and hundreds of cultivars. Among these species are herbaceous perennials, climbers, evergreen shrubs and succulents. The important point to note is that Begonias are native to tropical and sub-tropical regions. So the perennial begonias have to be treated as annuals in frost prone regions or brought in under heated glass in winter.

3.   Are tulips annuals or perennials?

Originally, tulips were all perennials that re-grow each year. However, after years of cross-breeding to create more colour variations, not all varieties act as perennials. Instead, most tulip bulbs need to be planted afresh each year. The exception is the species tulips, which have not been cross-bred. These will come back yearafter year.

4.   Chrysanthemums – Are mums perennials or annuals?

Chrysanthemums are the trademark autumn/fall flowers with their beautiful, eye-catching colours. Fundamentally, Chrysanthemums are perennials. Many species are hardy, but some, typically in the florists chrysanthemum grouping will not tolerate frost and will need to be lifted and brought into a heated greenhouse of conservatory for winter.

5. Are Zinnias annuals or perennials?

Some species of Zinnia are annuals, some are perennials and some are even shrubs. Annual Zinnias include Zinnia elegans. All Zinnias are tender, so even the perennials are usually grown as annuals in frost prone regions.

6. Are pansies perennials?

Garden Pansies (Violas) are biennials or short-lived perennial.

Final thoughts: the difference between annuals and perennials

The key difference between annuals and perennials is life cycle. Annuals live for one growing season only, whilst perennials live for two years or more.

This difference also has a bearing on how we propagate the different categories of plants. Annuals are usually grown from seeds, although it is possible to take cuttings from annuals. Perennials can usually be reproduced vegetatively, for example by division or by stem or root cutting, as well as being grown from seed.

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