PERENNIALS

What Is A Perennial Plant?

All plants can be divided into three categories. They can be annual, biennial or perennial. Perennial plants are those which come back each year. Annuals grow over one season. Biennials have a two-year life cycle. But perennial plants have a lifecycle that continues over several years.

Some perennial plants are herbaceous. This means they die back in winter before springing back into life the following spring. But others, like certain trees and shrubs, will remain in leaf throughout the whole year.

Trees and shrubs are technically perennials. But when people talk about perennial plants, they are sometimes referring specifically to herbaceous perennial flowers, herbs, vegetables, or other non-woody plants that remain in the garden year after year.

Popular Perennials Grown In The UK

Most of the most popular perennials grown in the UK are flowering plants, grown for their ornamental appeal. Though this is by no means an exhaustive list, some popular perennial flowering plants are:

It is important to recognise, however, that perennial plants can also be herbs or vegetables. You will find plenty of examples of perennial plants in these categories too.

Common perennial herbs include Mediterranean herbs like rosemary, thyme and oregano, for example. Amongst perennial vegetables, common examples are rhubarb, asparagus, Jerusalem artichokes and globe artichokes. But there are also many perennial plants in the cabbage family. And perennial alliums (onion family plants) too.

Exploring the edible potential of perennial plants can help you to create a garden that is not only beautiful and low maintenance, but which feeds you and your family too.

When creating perennial beds and borders, be sure to consider edible perennials, and trees and shrubs, as well as perennial flowering plants.

What Conditions Do They Prefer?

perennial garden filled with roses

Perennials are a wide group of plants, that can differ greatly in their requirements. Not all will enjoy the same conditions. It is important to recognise the needs of the plants you are considering. And to choose perennial plants suited to the conditions in your garden.

When choosing perennial plants for your garden you should be sure to think about:

  • If you want perennials for full sun, perennials for light or dappled shade, or perennials for deep shade.
  • Whether the plants need a sheltered spot, or can cope with a more exposed location.
  • The soil type, conditions and pH particular perennial plants will prefer.

Thinking holistically about garden design, it can also be helpful to think about the following when deciding which perennials to plant and where to plant them:

  • When the perennials will be in bloom (and wildlife required for pollination). Try to choose perennials so that you have flowers in bloom in your garden throughout as much of the year as possible.
  • How you can layer plants in space and time. Think about planting a wide variety of perennial plants that like similar conditions and complement one another. Remember, companion planting involves choosing plants that aid one another in a variety of different ways, not necessarily just how good they look next to one another.
  • Integrating perennial flowers with perennial edibles, trees and shrubs. Integration rather than segregation can help you make the most of your space. You can also think about integrating biennial or annual plants with perennial plants in your garden. Self-seeders can be good choices for a low maintenance perennial bed or border. Biennial foxgloves and annual borage are just two examples of ready self-seeders that could be at home in a perennial planting zone.

What Conditions Should You Avoid?

It is important not to place a shade loving perennial plant in full sun, or sun-loving perennials in deep shade. Again, understanding the environmental needs of the different perennials you are considering will help you avoid choosing the wrong plants for the wrong places.

Remember, perennials are plants that will remain in your garden for several years at least. So it is important to place them where they will not be disrupted by the needs of annual plants or crops. They are ideal for a bed, border or growing area that you would like to maintain but not intensively manage. This is why perennial plants are a good choice for those looking for a low maintenance garden.

Frequently Asked Questions

Annual vs Perennial – What’s The Difference?

Annual plants complete their life cycle in just one year. You will plant, grow and potentially harvest them over one growing season. Annual plants include a range of common garden flowers, certain herbs and many common vegetable crops.

Perennial plants, on the other hand, live for more than one year. Short-lived perennials will live for a few years, while more long-living plants can endure in your garden for years to come.

If you are trying to decide whether to grow annual or perennial crops in your garden, you need to think carefully about what exactly you want.

Annual crops can be beautiful, and/or beneficial for the yields they provide. Since they will die back or be harvested before the end of the year, they leave space for other plants to be placed into the spots in your garden they have vacated. Some annual plants may self-seed, and pop up again in your garden the following year if they are left to mature naturally.

However, it is worthwhile noting that annual plants generally require more work and commitment from the gardener.

Perennial plants generally require a lot less work than annual ones. Often, they can be planted and then left more or less to their own devices. They can therefore be a good choice for busy gardeners. Another thing to bear in mind is that choosing perennial plants can be an eco-friendly choice. Perennials remain in place, so protect the soil, benefit wildlife and sequester carbon more effectively than the crops in an annual garden.

Of course, you will have to remember that perennial plants will remain in place. So you cannot ring the changes and introduce new schemes each year.

What Is A ‘Hardy Perennial’?

A ‘hardy perennial’ is a perennial plant that can survive in your garden over the winter months. In colder climate zones, if you want to make sure that plants will remain in place over the years, it is important to choose perennials that can survive the winter temperatures where you live.

In the UK, the RHS has developed a hardiness rating, that will let you know the winter temperatures at which certain plants will survive. A hardy perennial will typically have a hardiness rating in the UK of between H4 and H7.

  • H4 – plants will survive an average winter in most parts of the UK (minus 5 to minus 10).
  • H5 – plants will make it through even a cold winter (minus 10 to minus 15).
  • H6 – plants will survive a very cold winter, across the British Isles (minus 15 to minus 20).
  • H7 – plants are extremely hardy and will endure in even the coldest conditions (below minus 20).

In some mild/ coastal areas, half-hardy perennial plants (H3) will also make it through the winter months.

What Is A ‘Herbaceous Perennial’?

A herbaceous perennial plant is one that has non-woody stems and foliage that usually die back over winter. Herbaceous perennials will remain alive in their root systems below the ground. They will regrow vegetative growth come spring.

Some herbaceous perennials are deciduous and lose all their leaves, while some retain dead or dying growth all winter long. A few, such as perennial grasses, are evergreen and retain green foliage over the winter months.

These herbaceous perennials stand in contrast to shrubs and trees, which are also perennial but which have woody growth above the ground even when not in active growth.

When Should You Plant Perennials?

Some perennials can be planted out at any time of the year, but generally speaking, herbaceous perennials are best planted in spring or autumn. These are the times when the soil will be workable, and temperatures are neither too warm nor too cold. The conditions at these times of the year mean that transplant shock should be kept to a minimum.

However, when exactly you should plant perennials will depend on which plants you have chosen and what weather conditions are like where you live.

Trees and shrubs can generally be planted out any time over the dormant period, between late autumn and early spring (as bare root specimens). However, again, the best time to plant will depend to an extent on the varieties you have selected and environmental conditions in your area.

Herbaceous perennials are often propagated by means of cuttings or division. Softwood cuttings are fresh, green growth taken early in the year. Semi-ripe cuttings are taken a bit later. And hardwood cuttings from shrubby perennials are often taken in autumn.

If you are sowing seeds, rather than planting ready-grown perennials, then it is often best to do so in spring. However, when seeds should be sown will also depend on varieties, climate and conditions.

When Is The Best Time To Move Perennials In The UK?

Perennials are best moved in autumn, when water uptake has slowed and transplant shock will be minimised. A number of perennials can also be moved in early spring, so this can be the second-best time. The worst time to move perennials is in midsummer, when temperatures and water requirements are both high.

Perennials of most types are best moved when they are in their dormant phase, so try to wait until mid to late autumn, or undertake the work early in the spring.

Autumn is also a good time to lift and divide mature herbaceous perennials to make new plants. And this can also ease congestion or overcrowding in a bed or border.

When Should You Cut Them Back?

Typically, flowering perennials are cut back after the plants have flowered. However, it can be beneficial to leave stems and some dying foliage in place over winter for the benefit of wildlife in your garden. Some perennials also look good when left to stand over the coldest months.

Depending on your preferences, you can zealously cut back foliage after the plant has flowered. Or you can put of with some wildness over winter and cut it back in early spring.

What Are The Easiest (Low-Maintenance) Perennials To Grow In The UK?

Most hardy perennials are great low maintenance choices for a UK garden. They generally require very little care and can withstand even the most neglectful of gardeners far better than most annual plants.

Trees and shrubs that require little care and which are very low maintenance include native options, which are well suited to the conditions where you live. For clues about which woody perennials to grow, it can be helpful to look at what is already growing well in your area.

Herbaceous perennials also often require very little maintenance and care. Remember, many common and persistent weeds are perennial plants. Some plants often considered to be weeds can actually be beneficial. They can sometimes make great choices in a mixed perennial planting scheme.

Here are five perennial flowering plants that can be excellent choices for a low-maintenance garden:

  • Alchemilla mollis – survives in almost any UK garden, in full sun, partial or full shade, in most soil types and pH levels.
  • Centaurea (Perennial cornflowers) – most soil types in full sun or partial shade, great for informal prairie planting schemes, for example.
  • Hardy geraniums – again, a versatile choice that can cope with a wide range of conditions.
  • Salvias – varied, with many long-flowering varieties to choose from for a sunny spot.
  • Sedums – varied and versatile – many great for drought-tolerant planting schemes.

Of course, these are just a few examples and there are many great low maintenance perennials to consider for your garden. Remember, a low maintenance plant will always be a plant well suited to the conditions where you live.

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