What Are Annual, Perennial & Biennial Plants?

Annual, Perennial & Biennial Plants

If you have ever noticed plants that seem to come back every year or only last a year then you will know there is a difference between the life cycles of different plant species. Annual, perennial and biennial are how we describe these life cycles.

What Is The Difference Between Annuals, Perennials, and Biennials?

Understanding how these plants differ from each other will help you choose what types of plants you want to include in your garden and how you’ll need to take care of your garden throughout the year. 

The difference is in the lifecycles and how long they last. All plants want to reproduce, to set seed and the way they do this is what causes these differences.

Annuals grow, produce lots and lots of flowers which then go to seed and these are spread and the plant dies. Next year, the seeds produced by the annual restart that cycle.

Perennials last much longer. They take a longer time to grow to maturity, usually 3 – 5 years, they produce fewer flowers but still produce seed. Perennials will grow every year but some of the more tender, leafy perennials will start to diminish after 4 or 5 years.

Biennials last two years, the first year they produce strong roots and leaves and then in the second year will flower and set seed. After two years the plant will die and the seeds will restart that same two-year lifecycle.

There Is Some CRossOver

While it is important to recognise these categories when you come to buy and choose plants there is some crossover. As an example, you can get annual varieties of perennials such as delphiniums. In most cases, you buy the seed to grow annuals and are more likely to get perennials grown by nurseries.

There are also short-lived perennials that do not flower well after their second year so they can considered biennials and can be taken out of the garden after a couple of years.

What Are Annual Plants? 

What Are Annual Plants
Sweet Peas

Annuals are plants that have a one-year life cycle. You’ll plant a seed in the spring, the plant will grow and bloom—producing more seeds, and then die in one growing season. Annuals do not come back every year and need to be replanted or left to reseed. 

Annuals are popular choices for gardeners who love to work in their garden because they will need to plant new each year. 

Annuals are also known for their beautiful, bright flower colours with some of the most popular choices, including petunias, zinnias, and marigolds. The blooms last for a long time from spring through to autumn. 

Annual Plants Calendula
Calendula

Some of the easiest annuals to grow by seed include:

  • Sunflower
  • Marigolds
  • Morning glory
  • Bachelor button
  • Calendula
  • Castor bean
  • Cosmos
  • Nasturtium 
  • Sweet pea
  • Sweet alyssum 
  • Larkspur
  • Poppies 
  • Zinnia
  • Hyacinth bean 

These annuals are easy to start from seed often just sowing them right where you want them to grow. Just follow the directions for planting on your seed package. Make sure to wait until after the last frost of the season to plant, and you’ll have colourful, vibrant flower gardens by late spring. 

What Are Perennials?

What Are Perennials
Verbena Bonariensis

Perennial plants are herbaceous green plants that still produce flowers, usually to a lesser extent than annuals and live for at least two years or more. 

Perennials do grow back each year until the plant reaches maturity, which can be around five years, although trees, bushes, and other flora that live much longer are also considered perennials. 

There are two classifications of perennials. Deciduous perennials are the type most used by gardeners and landscapers and plants that grow during the warm months and go dormant in the cold months. Evergreen perennials are able to grow all year round, such as holly and boxwood.

Perennials have a shorter blooming season with flowers lasting only a few weeks in most varieties. 

There are also those perennials that have bulbs that can be planted in the garden. Tulips, Lilies, and daffodils, for example, are some of the most popular choices for garden perennials. 

Flowering Perennials

Peonies Perennial
Peonies

Although perennials do not need to be replaced each year, some of these plants, like tulips, lilies, and irises, can notice a decline in the size of their flower, how tall and thick they grow, and need to be divided or replaced every three to five years. 

Hardier perennials can last for twenty years or more, however, when the gardens are tended and soil quality, water, and weather conditions are great. 

Something else you must take into consideration with perennials is the regional differences in climate. A perennial like snapdragon that can grow all year round in warm climates is considered an annual in places that experience cold winters because the plant cannot withstand the cold. 

Perennials that are temperature-dependent are often referred to as “frost-tender perennials.” These perennials can survive all year round in colder climates if the garden can avoid frost by bringing the plants inside during the winter like many do with potted lemon trees, or covering with tarps during nights where frost is expected. 

Some of the easiest perennials to grow in your garden include:

  • Peonies
  • Garden Phlox
  • Blanket Flower
  • Russian Sage
  • Asters
  • Daylilies 
  • Purple Coneflowers
  • Yarrow 
  • Threadleaf
  • Black-eyed Susan 
  • Siberian Iris 
  • Penstemon 
  • Moss Phlox 
  • Coral Bells 
  • Chrysanthemum 
  • Asiatic Lily
  • Hosta

What Are Biennials? 

What Are Biennials
Sweet William

Biennial plants are less common and have a different lifecycle than both the perennials and annuals because they grow for only two years. 

The first year a biennial is planted, it will be green and survive through the winter. The following year, the biennial will produce blooms, go to seed, then die. Biennial plants that are popularly used in gardens include foxgloves and hollyhocks. 

Biennials’ two-year life cycle means that your garden will also have a different look every few years with less effort than a garden full of annuals that need to be replanted each spring. The first year when they are green, they are storing energy to produce very lush foliage with bright blooms and lots of seeds in their second year. 

Biennial Forget Me Nots
Forget Me Nots

Some of the easiest biennials to grow in a garden include:

  • Canterbury Bells 
  • Forget-me-nots
  • Foxglove
  • Hollyhock
  • Honesty 
  • Sweet William

Allowing Biennials To Self Seed

Although the two-year life cycle is the natural course for these flowering plants, it is possible to keep your garden blooming every year without having to replant completely by allowing the seeds from the biennials to fall and create from seedlings at the end of their life cycle. This will start a pattern of growing and flowering different plantings so that there are blooms on some of the plants each year. 

Bell Flower
Bell Flower

Combining Annuals, Perennials And Biennials

Many gardeners use a mix of annuals and perennials in their gardens, with some biennials thrown in too. 

Mixing these types of plants creates a colourful, blooming flower garden from spring to fall while also have a lush, green backdrop with hardy plants to set off the colours and scent of the flowers you’re growing.

Annual flowers are especially good to fill in the gaps between your perennials so your garden is full and lush all year round. 

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