Biennials to sow in June and July
Start to sow these biennials in June and July. Summer is an ideal time to sow seeds for next year’s flower display. Biennials are plants that grow roots and leaves during their first year and then produce flowers and set seed during the second year. There are also perennial plants that are often grown as biennials because they are short-lived as perennials or are likely to succumb to disease if grown into a third year.
Every year I wish I had been more organised the previous year and sown plenty of seeds. So here is a short checklist of some of the biennial seeds you can sow now.
Campanula medium
Canterbury bells are easy to grow biennials, with an upright habit that produce a mass of bell-shaped flowers. The petals turn back on themselves creating the effect of the rim of the bell. I grew a selection of dark purple, pink and white plants when we first moved to our new home. They looked great among other cottage favourites, and some of the plants flowered for two years before dying. Height 75cm and 30cm spread. I valued the colour and interesting flowers highly, but I found that in the very damp spring we had, the foliage was a great hiding place for hungry slugs. While they mostly left the Campanula medium alone, they devoured many young plants around them.
Delphinium ‘Magic Fountains Lilac Pink White Bee’
These short-lived perennials are often grown as biennials. Give delphinium fertile soil and a sunny, sheltered position and they can provide a tower of flowers. This series offers a more compact plant that reaches around 90cm in height from early to late summer. Young growth can be susceptible to slug and snail damage; try growing them in pots until the plants are 20 – 25 cms tall before planting out into the garden. They should not need staking. Deadhead flower spikes to encourage it to flower again. Delphinium are available in a wide range of colours including purples, true blues, pinks, reds and whites and the Magic Fountain series are a shorter variety that are ideal for small gardens, pots and windier sites.
Digitalis
Here are some easy biennials to sow in June and July. Foxgloves are easy to grow short-lived or biennial plants. Give it the right conditions of moist, but well-drained soil (much like you’d find on the edges of woodland) and Digitalis purpurea, the common foxglove, will grow to 1 to 2 metres and will seed itself in your garden for years to come. There are plenty of varieties, offering a wide range of colours and heights, most grow a rosette of leaves in the first year and flower the following year. I think they look best when several are grown together. Remove flower spike once flowering is finished unless you want to collect seed or allow it to self-seed in your garden. Be careful when handling as all parts of the plant are poisonous. I spotted these apricot or peach Digitalis at RHS Chelsea 2025.
Alcea rosea
Hollyhocks are short-lived perennials that are easy to grow from seed and make an impressive display in the garden. I like the large pom-pom flowers of Alcea rosea ‘Chaters double’which are available in a wide range of colours and who could resist something as dramatic as the almost black flower of Alcea rosea nigra. Grow them against a wall or near the back of the border, or position a few plants together in the centre of a bed for splash of colour that rises above other herbaceous perennials and annual flowering plants.
Last year I grew some of the seeds that were free on the front of Amateur Gardening and they’ve already produced some beautiful flowers.
Lunaria
The purple or white flowers appear in late spring, followed by attractive seed pods that open to reveal the seeds against a silvery disc. This biennial grows to 60cm height and 50cm spread. It will self-seed freely, or collect the seeds and grow in pots to plant out during the first year. Honesty grows happily in all, but clay, soils and is hardy across the UK. I have both the purple and a white, variegated variety because it is such a great doer in the garden. So, I was pleased to see it being used in a garden at RHS Chelsea in 2025.
Erysimum cheiri
Another short-lived perennial that is most often grown as a biennial. Wallflowers are not only grown for their cheerful, colourful flowers, but for their sweet scent. Grow in well-drained, neutral or preferably, alkaline soil. It will struggle to grow in clay soils. Erysimum cheiri prefer full sun. Height and spread depend on variety, but expect 40cm – 75cm height and up to 40cm – 60cm spread. The good news is that if you miss sowing your own seeds, you can often buy young plants in the late summer or autumn to transplant into your garden. Available in a wide range of colours including white, pinks through to dark burgundy red, purples, yellows and oranges.
Hesperis matronalis
Commonly known as Sweet Rocket, you’ll find it with purple or white flowers. It’s ideal for borders where you want fragrance as well as colour, as it fills the surrounding air with a sweet scent. I particularly like the white form, which almost looks like it glows at dusk. It can be grown as a short-lived perennial or biennial and it reaches 90cm height. Hesperis matronalis prefers neutral and alkaline soils, in full sun or partial shade. And is hardy across the UK and Ireland.
Oreomecon nudicaulis
Icelandic poppies are easy to grow and are often grown as annuals. However, you may get earlier flowering and stronger plants by sowing now for flowering next year. Sow seeds in biodegradable pots, and plant out with the pot, to help reduce root disturbance or scatter seeds outside where they are to flower. Do not cover the seeds as light helps germination. Grow in full sun in any soil, except clay. They like well-drained soil in a west- or south-facing position. Height 45cm – 60cm. Hardy across UK, Ireland and Europe, even during the harshest of winters.
Angelica archangelica
I like the exuberance of this plant in full flower. Despite the tiny, individual flowers being a fairly dull yellowy-green colour, it is the impact of the shape of the umbels and height of the plant that appeals to me. Angelica archangelica is another perennial that is often grown as a biennial. Height up to 250cm and spread 100cm. Hardy across the UK and Ireland. Grow in partial shade in moist, but not water-logged, clay or loam soil.
More information
The article ‘Biennials to sow in June and July’ was written for Amateur Gardening magazine in summer 2025. I may have updated some of the specific varieties and images. Links are included to help you find biennial’s seeds for the suggested plants that you can sow during summer. Check out vegetable seeds to sow now in my guide of Veg to Sow This Month.
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