Many of the most popular garden plants we enjoy growing are often described online, in books or on their labels as being ‘herbaceous’ or ‘woody’, ‘deciduous’ or ‘evergreen’. Then there are trees, shrubs, annuals or biennials, or quite often perennials.
Although these terms can sound off-putting and confusing, they are all helpful words that relate to the way a plant grows, describing its life cycle and the growth it develops. These terms also give us clues to help understand how a particular plant is likely to perform in the garden, and even hint at what its needs and care requirements might be.
Perennials: plants that live from year to year
Put simply, a perennial plant is one that survives for more than two years. Knowing a plant is perennial is often good news as we can expect it to grow and multiply over the years, without having to regrow it from seed, or return to the garden centre next year to replace it.
Strictly speaking, the word perennial also relates to woody plants such as trees and shrubs (woody perennials), but in practice the word is used as shorthand for ‘herbaceous perennial’.
Herbaceous perennials are plants that grow every year, producing stems, leaves and flowers, but do not make woody growth above ground. They die down to soil level at the end of the growing season, becoming dormant and escaping adverse winter cold, only to reappear again the following year.
Perennials that die down at other times, or not at all
In some cases, plants in the wild are adapted to retreat below ground to escape extreme summer heat and drought, so some perennial garden plants actually die down after spring. Examples include plants such as irises, and bulbs and corms including daffodils, crocus and snowdrops. These plants are perennials but will be dormant in summer.
There some perennials that do not die down at all. A few popular garden plants such as phormiums, Kniphofia, Bergenia, hellebores and some ferns, grasses and sedges are evergreen herbaceous perennials: they also live from year to year and do not make woody stems, but they do have evergreen leaves.
With our increasingly mild winters, some plants that normally behave as perennials will continue growing. Plants such as Melianthus and some salvias that in milder climates are shrubby, will normally die back to a woody rootstock when grown in the UK, due to the cold.
When is a perennial not always perennial?
The term ‘tender perennial’, which is used for plants such as pelargoniums, coleus and some salvias, can be confusing. You might see the word perennial and assume these plants will come up in your garden each year, but in these cases plants are frost-tender. That means they will only survive if kept away from cold, which usually involves moving plants under cover.
Often, tender perennials are treated by gardeners as annuals - plants that live for just one year. By the same token, a few plants often sold as annuals are also in fact perennials: petunias, for example. In these cases, plants may last for longer than a year, but are often less attractive or useful if they manage to make it through winter.
Frequently Asked Questions
How long do herbaceous perennials plants live? This is highly variable. Some perennials are naturally short-lived, surviving for three or four years, while others typically last for around six to 10 years, or longer if they are cared for and regularly divided and replanted to keep them healthy. Some perennials such as peonies, many bulbs and others are much longer lived, potentially surviving for decades.
Do herbaceous perennials need as much care as annuals? This can vary and depends partly on how well suited they are to conditions in your garden. In some respects, herbaceous perennials deserve more care as they will then bring enjoyment for many years to come. Most benefit from an annual mulch, regular deadheading and then every few years, dividing of the clumps to keep them in good growth. Once established they need less regular care than annuals, although watering and feeding may still be required.
Can I keep perennials in pots? Yes, many perennials will grow well in containers and continue to grow from year to year. You will, however, need to repot them into larger pots of fresh compost as they grow, and divide plants when they get old or become too big.
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