How to grow annuals and biennials

What are annuals and biennials?

Annuals

Annuals are plants that complete their life cycle in one growing season. They are generally easy to grow from seed or can be bought as young plants from garden centres. Annuals are ideal for growing in summer containers and filling gaps in borders. Some examples of annuals include sunflowers, cosmos, sweet peas and zinnia.

are fast-growing plants that flower, produce seeds and then die, all in just one year. They can be hardy (able to withstand winter outside), semi-hardy or tender (killed by frost). Most can be grown easily and cheaply from seed, or bought as young plug plants

Seedlings or young plants grown singly in small modules, with the advantage that they can be transplanted with minimal root disturbance. Bedding plants and young veg plants are often sold as plug plants of various sizes, with smaller ones requiring more aftercare. They usually need to be potted up and grown on indoors until large enough to plant outside.

. They are grown for their colourful summer flowers and are ideal for filling gaps in borders or adding to hanging baskets and containers. Popular examples include cornflowers, cosmos, nasturtiums and petunias.

Biennials are often sown in summer to grow in their first year and then flower, set seed and die in their second year. They are easy to grow from seed, or bought as young plants in spring. Examples include foxgloves, wallflowers and honesty.

Choosing annuals and biennials

These plants come in wide range of colours, sizes and styles, from native

A native plant is one that originated or arrived naturally in a particular place without human involvement. In the British Isles, native plants are those that were here during the last ice age or have arrived unaided since.

wildflowers to more exotic, tender types. Annuals in particular are ideal for adding colour quickly, easily and cheaply, flowering within just a few months of sowing.

• Hardy annuals are the easiest to grow, and can be sown outdoors where you want them to flower. Half-hardy and tender annuals take a little more time and effort, as they are mostly sown indoors and given gentle warmth in spring, before planting out once there’s no risk of frost, usually from late May.
• Bedding plants are usually treated as annuals too – they flower through the summer and are then removed once their display is over.
• Biennials are easy to grow from seed too, but take a little longer to flower, usually in their second year from sowing. They’re often sown indoors, but hardy types can be sown outdoors too.

As these plants are so cheap and short-lived, you can grow lots of different types or change what you grow every year. There’s no big commitment or great expense involved, so you can experiment and have fun.

Getting the right look

Consider what you want from your plants, such as:

• Colour – this is usually the main factor when choosing annuals and bedding, which come in almost every colour imaginable. Do you want bright exotic hues for cheery hanging baskets and containers, or more restrained pastels to complement other perennial flowers, grasses or bulbs in your borders?
• Style – do you prefer the natural look of native wildflowers, to weave among ornamental grasses, or something more exotic and eye-catching, such as a nicotianas, cleome or California poppies? See our guide to easy exotics from seed.
• Size – most annuals and bedding plants
  

  Bedding plants are usually colourful half-hardy, short-lived or annual plants, grown for displays in beds or containers. They may be changed seasonally, with spring, summer and winter bedding displays each using different plants of appropriate hardiness and flowering times.

  are fairly small, as they have a short growing season
  

  The period of time when an individual plant is in active growth. This will depend on the local climate and light levels, and can vary between different plants, although it is broadly from spring to autumn.

  . They tend to reach 90cm (3ft) at most, but a few grow larger, the most well-known being sunflowers, which can easily stand several metres tall. Biennials, with their longer growing time, are often a reasonable size, with foxgloves getting to at least 2m (6½ft).
• Shape – do you want low groundcover, such as nasturtiums or petunias, for the front of a border or to cascade over the edges of a container? Or to add height, with tall spires such as foxgloves, or climbers such as sweet peas and morning glory? The choice is yours!
• Fragrance – some annuals and bedding are wonderfully fragrant, so are ideal for growing near a path or seating area. Sweet peas, nicotianas, heliotrope and night-scented stocks, among others.
• Wildlife friendliness – if you want to attract more wildlife, choose pollinator-friendly flowering annuals and biennials. A few, such as sunflowers and teasels, provide seeds for finches in late summer.

How and what to buy

Annuals and biennials are available all year round as packeted seeds, and usually in spring as plug plants or young plants, although the choice will be more limited. You can buy them in garden centres or online.

Where to get ideas and advice

To explore and narrow down your potential plant choices, you can:

• Visit gardens that feature lots of bedding, wildflowers and other annual plantings, to see which you like. All the RHS Gardens feature impressive displays of annuals and bedding, and all the plants are labelled, so you can note down your favourites.
• Ask at nearby garden centres, which should offer young plants in spring and a range of seeds suited to your local conditions.
• Search our listing of annuals and biennials, to browse the photographs and plant descriptions. You can narrow down your search by specifying your growing conditions and/or plant preferences.
• Browse the many seed suppliers’ mail-order catalogues and websites.

See also our guides to:

• top ten hardy annuals
• easy half-hardy annuals

When to sow and plant

Hardy annuals

Annuals are plants that complete their life cycle in one growing season. They are generally easy to grow from seed or can be bought as young plants from garden centres. Annuals are ideal for growing in summer containers and filling gaps in borders. Some examples of annuals include sunflowers, cosmos, sweet peas and zinnia.

can be sown or planted outside in spring or autumn, as they can survive frost. Autumn sowings will flower earlier.

Half-hardy or tender annuals, which can’t tolerate cold weather, are mostly sown indoors in spring, to be planted outside after the last frost. Those which flower quickly from seed, are also successful when sown outdoors in early summer.

Hardy biennials are usually sown in summer. Young plants can be planted outside in autumn or spring.

Where to plant

Most annuals, biennials and bedding like a fairly sunny spot, although a few will tolerate some shade. See our shade plants guide.

They can also be planted in summer containers, including large patio pots, hanging baskets and windowboxes.

How to sow annuals and biennials

Prepare your soil

When sowing directly into a border, clear the area of weeds, then rake the surface to a fine, crumbly texture.

How to sow

Hardy annuals are easy to grow from seed, and are usually sown outdoors in spring or autumn – see our sowing guide for full details. To find out which hardy annuals to sow when, see our spring sowing guide and autumn sowing guide.

You can also sow annual wildflowers in a meadow-style planting – see our guide to creating a wildflower meadow and our step-by-step mini-meadow.

Half-hardy and tender annuals, and most bedding, won’t survive frost, so are usually sown indoors in spring, to be planted outdoors after the last frost. See our guide to sowing indoors.

If you don’t have space indoors, you can sow fast-growing types outside in early summer, but they will flower later than spring-sown plants. See our guide to sowing half-hardy annuals outdoors.

Biennials are hardy usually sown in summer – and planted out into their flowering positions in autumn.

If you don’t have the time or space to sow seeds, all of these can also be bought as young plants, usually in spring.

They can also all be planted in containers – see our guide to planting up containers and how to plant a hanging basket.

Watering

Water seedlings

A seedling is a young plant grown from seed.

and young plants regularly for the first few months. After that, plants growing outdoors should only need to water in dry or hot spells. However, these fast-growing plants don’t have time to develop extensive root systems, so do keep a close eye on them. See our guide to watering wisely.

Plants in containers, such as hanging baskets, patio pots and windowboxes, need regular watering all summer, as they dry out very quickly. See our tips on container maintenance.

Feeding

Most annuals

Annuals are plants that complete their life cycle in one growing season. They are generally easy to grow from seed or can be bought as young plants from garden centres. Annuals are ideal for growing in summer containers and filling gaps in borders. Some examples of annuals include sunflowers, cosmos, sweet peas and zinnia.

and biennials don’t need additional feeding when growing in borders. But to boost flowering, especially with bedding plants

Bedding plants are usually colourful half-hardy, short-lived or annual plants, grown for displays in beds or containers. They may be changed seasonally, with spring, summer and winter bedding displays each using different plants of appropriate hardiness and flowering times.

and those in containers, you could apply a potassium-rich liquid fertiliser, such as tomato feed

A potassium-rich liquid feed to encourage flowering and fruiting in various plants, not just tomatoes. Take care to follow the instructions on the packet.

, every couple of weeks. See our guide to fertilisers.

You can also add slow-release fertiliser to the compost

Can refer to either home-made garden compost or seed/potting compost:

• Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

when planting up containers with bedding, to maximise flowering. See our guide to planting up containers.

Weeding

Weeds will compete with your plants for light, water and nutrients

To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key nutrients usually taken up from the soil are nitrogen, phosphorus and potassium. Plants also need carbon, oxygen and hydrogen to make carbohydrates — their main energy source. Carbon and oxygen come from the air as carbon dioxide, while hydrogen is drawn from water absorbed by the roots. Other important soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough of these nutrients to support healthy plant growth.

, so remove them regularly. See our tips on controlling weeds.

Deadhead plants regularly to encourage more flowers.

Most annuals

Annuals are plants that complete their life cycle in one growing season. They are generally easy to grow from seed or can be bought as young plants from garden centres. Annuals are ideal for growing in summer containers and filling gaps in borders. Some examples of annuals include sunflowers, cosmos, sweet peas and zinnia.

and biennials can be propagated from saved seed, although if your parent plants are hybrids or cultivars, then the new plants may not be exactly the same as the parent plant. See our guide to collecting and storing seed.

Most annuals

Annuals are plants that complete their life cycle in one growing season. They are generally easy to grow from seed or can be bought as young plants from garden centres. Annuals are ideal for growing in summer containers and filling gaps in borders. Some examples of annuals include sunflowers, cosmos, sweet peas and zinnia.

and biennials are trouble free, as long as they’re grown in the right conditions to suit their needs – check the seed packets or plant labels for details when buying.

Bedding and young plants, however, may be attacked by slugs and snails when growing outdoors.

Seedlings

A seedling is a young plant grown from seed.

growing indoors can be vulnerable to damping off.