As summer plants are in full bloom, gardeners are already turning their attention to planning for next year’s plans for their outdoor space. June is the perfect month to sow biennial plants that will burst into life the following spring and summer. British Garden Centres has put together its top biennials to be sown now to ensure a spectacular garden show next year.

What is a biennial?

Quite simply, biennials are plants that complete their life cycle over two years. In the first year, they establish a robust root system and foliage, and in the second year, they will reward your patience with stunning flowers. This two-year growth pattern makes biennials an excellent choice for gardeners who want to plan ahead and enjoy a succession of beautiful colours.

Top biennials to sow now

Here are some of the best biennials to sow in the UK this June, each offering distinct beauty and garden benefits:

Foxgloves: These are among the most iconic biennials, known for their towering flower spikes that can reach up to five feet tall. Their bell-shaped flowers come in shades of pink, purple, white, and yellow, attracting bees and other pollinators. Foxgloves thrive in well-drained soil and prefer partial shade, making them ideal for woodland edges and cottage gardens.

Sow your foxglove seeds thinly in seed trays or modules indoors or in a cold frame during June. Once seedlings are strong enough, they can be planted outdoors in late August or September. Foxgloves are also excellent self-seeders, so once established, they often return year after year,

Lunaria: Also known as Honesty, this biennial plant showcases purple or white flowers and distinctive silver, coin-shaped seed pods that add interest to the plant after the flowers have faded. Lunaria grows to about three feet tall, so it is great for the back of borders and thrives in well-drained soil and partial shade. You can sow the seeds directly into the soil or in seed trays in June.

Dianthus: Commonly known as Sweet William, Dianthus is a biennial with clusters of fragranced flowers in shades of red, pink, white, and purple. They are perfect for borders, rock gardens, and containers. Sweet Williams prefer full sun and well-drained soil, and seeds can be sown in June either directly in the garden or in trays. Transplant seedlings outdoors once they are sturdy enough.

Wallflowers: Erysimum is a traditional biennial with fantastic scent, colourful flowers in yellow, orange, red, and purple. They are easy to grow and thrive in sunny spots with well-drained soil and will bloom for months come spring. Now is the time to sow your wallflower seeds in June or July in seed trays or directly in the garden. Wallflowers are excellent for attracting pollinators and work well in mixed borders or alongside spring bulbs, so get sowing this biennial now to get your garden buzzing early next year.

Hollyhocks: These are a great biennial to sow in June because they grow well when planted outdoors in late spring or early summer. They like a sunny spot with well-drained soil, such as along a fence or wall, which helps protect them from wind. When you sow the seeds now, the plants will grow leaves and roots this year, then flower beautifully next summer, adding height and colour to your garden. Hollyhocks are easy to care for, needing only occasional watering and staking if they get tall. They also produce seeds that can drop and grow new plants the following year.

Scatter the seeds on the soil surface or plant in pots, keep the soil moist, and choose a sunny, sheltered place. Once established, hollyhocks need little attention and will bring lovely flowers and attract pollinators like bees to your garden next year.

Iceland Poppy: Iceland poppies are often grown as biennials. They have beautiful bowl-shaped flowers in yellow, orange, red, and white. Seed sowing can be done in late spring, summer for blooms the following year. The best spot is somewhere with full sun or dappled shade and soil that is rich and drains well.

After germination, seedlings should be grown on and planted out from late August to September, allowing them to develop strong roots and foliage over autumn and winter, which leads to robust flowering in late spring. These poppies are easy to grow, but they don’t like to be moved once established, so sow them where you want them to flower or use biodegradable pots if starting indoors.

Campanula: A great biennial to sow in June, as planting at this time allows the plants to benefit from the warm soil and longer daylight, which helps seedlings establish well before winter. Campanulas are low-maintenance and attract beneficial insects like bees with their bell-shaped flowers, making them a great choice for adding height, soft colour, and wildlife value to borders and containers.

Plant in a seed tray or pots with moist, well-draining compost or potting mix. Once the seedlings have grown their first leaves and are large enough to handle, thin them out and transplant each seedling into individual pots. Grow them on in a cool, sheltered place like a cold frame. When all risk of frost has passed, harden off the plants by gradually exposing them to the outdoors, then plant them out in a sunny, well-drained spot.

June is the ideal month to sow biennials for your garden, setting the stage for a spectacular floral display next year. For gardeners looking to add colour and scent to their outdoor spaces with minimal fuss and maximum impact, biennials sown now are a smart and beautiful choice.