What Is An Annual / Biennial Plant?

An annual plant is a plant that completes its life cycle within one year. Many popular fruit and vegetable crops in a kitchen garden are annual plants, as are a range of common bedding plants or flowers.

Annual plants are typically grown from seed, though they can also be purchased from garden centres and nurseries as plugs or pot grown plants ready to place in your garden.

A biennial plant is a plant that completes its lifecycle over two years – growing in the first year before flowering and setting seed in the second.

Unlike perennials, annuals and biennials will not remain in place in your garden over multiple years. However, in the right conditions, certain annuals and biennial plants will self-seed readily. This means that the seeds will naturally mature and disperse around the growing area in which they are planted. And if you leave them to self-seed this does of course mean that you can continue to enjoy them in your garden year after year.

The benefit of including annuals and biennials in your garden is that you can ring the changes. If you do not choose readily self-seeding varieties then you can opt to grow different flowering plants or other annual plants every year.

Though growing them is usually a more high maintenance option than choosing only herbaceous perennials, shrubs and trees for your garden. And annual cultivation generally does not allow for as much carbon sequestration as perennial planting schemes.

In an organic garden, it is a good idea to introduce annual or biennial plants within mixed polycultures. Often, they are grown in addition to a range of perennial plants in sustainable garden design.

When it comes to a polyculture kitchen garden, for example, annual vegetable crops are often grown alongside companion plants. Companion plants will often include certain annual flowering plants and herbs – but perennial herbs are also often included.

Most gardeners who choose to grow their own will opt for typical annual crops – such as lettuce and other leafy greens, radishes, peas, beans, tomatoes, peppers, squash, cucumbers and more. And common biennial vegetables including carrots, parsnips, onions, leeks, and certain brassicas (members of the cabbage family). But it is also interesting to consider how annual or biennial flowers and herbs can be included in the design to benefit the system as a whole.

It is important to think about which vegetables growing in a kitchen garden are biennial if you wish to collect your own seeds. Biennial vegetables will usually need to be left overwinter to the following year in order for them to flower and set seed. Since these vegetables are usually harvested before their life cycle is completed, many gardeners are unaware of this feature of their life cycle. But if you save your own seed, it is important to recognise which crops are truly annual, and which are biennial.

Understanding what to do when in an ornamental flower garden also involves understanding which of your plants are annual and biennial, and which are perennial.

Popular Annuals Grown In The UK

As mentioned above, many of the common annuals and biennials grown in the UK are edible crops, grown in kitchen gardens. But these crops are covered in more detail on other categories of the site. So here, let’s take a look at some popular flowering plants that are annual or biennial:

Popular Biennals Grown In The UK

Here are some biennials, or short-lived perennials often treated as biennials in the garden:

Of course, there are many, many more annuals and biennials to consider. But these popular options mentioned above could be a good place to begin when looking for options for your garden.

What Conditions Do They Prefer?

zinnias visited by a butterfly

Annual and biennial plants are a huge and very varied range of plants. Some thrive in full sun, while others are happiest in the shade. It is important to choose annual and biennial plants for your garden based on the environmental conditions that are to be found there, as well as on your personal preferences.

Be sure to think about the sunlight and shade, temperatures throughout the year, rainfall levels and humidity, and whether the site is sheltered or exposed. Think about the local microclimate as well as the general climate zone in which you live.

When choosing annual or biennial plants for your garden, it is also very important to think about the soil type, conditions and pH level where you live. You will find annuals suited to growing on pretty much any site – but you do need to choose the right plants for the right places in order to have the best chances of success.

You can commonly grow a range of annuals or biennials in beds and borders, in raised beds or planters, or in containers.

What Conditions Should You Avoid?

Avoid planting annuals and biennials anywhere not suited to the growing conditions that the particular plants you have chosen require. Do not just choose plants for your garden based on what they look like, or the uses to which you want to put them. Annual and biennial flowering plants and food crops vary significantly in their needs and preferences.

Thinking about the conditions within a plant’s native range (if it is not a UK native) can help you determine where in your garden you might be able to grow them – and where you should not.

Frequently Asked Questions

Do Annual Plants Come Back Every Year?

Annual plants will not typically come back every year. Usually, you will have so sow new seeds each year or purchase new bedding plants in order to continue to enjoy them in your garden.

There is an exception to this, however. When some annual plants are provided with the ideal conditions, they will self-seed readily. In other words, their seeds will naturally mature if you let them. They will drop to the soil nearby or be dispersed through your garden through natural means. Those seeds should then, if they have the right conditions, germinate, and new plants will grow, usually the following spring.

Some annuals that can self-seed readily in the right conditions include:

  • Borage
  • Calendula
  • Cornflowers
  • Nasturtiums
  • Poppies

These are just a few examples.

One thing to note is that when talking about annual edible crops, we do not necessarily want self-seeding to take place. Allowing the occasional heritage variety of a common crop to self-seed could be interesting. But F1 hybrids will not come true from seeds – and the seeds that self-seed may not come true – or even taste good.

Certain flowering plants may also not come true from seed, or may take over your garden if you do not prevent them from self-seeding. So this is something else to bear in mind. Often, annual flowering plants are deadheaded, which of course prolongs the flowering season, but prevents seed formation from occurring.

What Are Some Common Uses Of Biennial Plants?

As mentioned above, many of the common crops grown in a kitchen garden are usually treated as annuals but are actually biennials. The properties of these plants must be taken into account if you would like to collect seeds from these plants. Carrots and onions are two common examples.

Another place where it is common to use biennial plants is in a mixed border, where they are often included among perennial flowering plants. Readily self-seeding types well suited to the conditions are often the best options to choose. Foxgloves, angelica, and viper’s bugloss are some excellent options to consider, for example. Though the toxicity of foxgloves should, of course, be taken into account.

Biennial plants, especially those that self-seed readily, can also be great additions to a perennial food-producing system, such as a forest garden, or a smaller fruit tree guild. Since biennials have to set seed to perpetuate themselves, they are commonly, like annuals, rich in nectar. And so can be great for attracting pollinators and other beneficial insects for pollination and pest control in an organic garden.

When Can I Plant Annuals?

The time for planting annuals will, of course, depend on exactly where you live, and which annuals you have chosen to grow. Typically, however, annuals’ seeds are sown indoors a brief time before the last frost date in your area. Or direct-sown once all risk of frost has passed.

It is also common to purchase plug plants or bedding plants that can be placed into your garden – often in the spring or early summer.

What Are The Best Annual Bedding Plants For Bees?

Many annual and biennial plants are fantastic for bees and other pollinators. As mentioned above, they need to flower and set seed to perpetuate, and so are commonly rich in nectar. This is great for bees and other pollinators, and can also help in attracting a wide range of insects to your garden that will eat pest species and help in keeping their numbers down in an organic garden.

The more flowers you have in your garden, the more bee-friendly it will be. One key thing to remember when choosing annual bedding plants for bees is that you should try to choose plants that bloom throughout as long a period of the year as possible. Think about making sure you have blooms throughout the seasons.

Single flowers (rather than complex flowers) are generally better for bees. (Think cosmos, calendula, and simple marigolds, for example. And it is a good idea to consider native flowers that are useful for wildlife native to your area (poppies, cornflowers etc..) Another interesting thing to note is that bees are most attracted to flowers that are blue/ purple or white. Though flowers in many other colours will also attract them. Borage is one of the very best nectar-producing annuals for bees. This plant is a veritable nectar factory, replenishing large quantities of nectar far more quickly than many other flowering plants.

Are Annual Plants Safe For Dogs?

Many annual plants are perfectly safe for dogs and other pets. However, there are a huge number of annuals and some do potentially carry some risks when it comes to human or animal toxicity. Always check toxicity information before introducing any new plants to your garden.

One interesting thing to note, however, is that many annual plants are not only safe for dogs, other pets and humans, but are actually suitable (and delicious) for us to eat. Common annual flowers that are edible include but are definitely not limited to:

  • Borage (edible leaves and flowers with a mild cucumber-like taste.)
  • Nasturtiums (Edible leaves and flowers, peppery and great in salads, and edible seed pods too.)
  • Sunflowers (Edible seeds, but also edible petals that can be added to a salad.)

Which Varieties Will Flower All Summer?

There are a wide range of annual flowers that will bloom over a long period, many that will flower all summer long. Some examples of summer flowering, long flowering annuals that you might like to consider include:

  • Begonias
  • Cosmos
  • Impatiens
  • Marigolds
  • Pelargonium
  • Petunias
  • Sweet peas

Though there are plenty more interesting and beautiful options to consider – when it comes to long-flowering annuals and biennials, and other, perennial, flowering plants.

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