Hardy annual plants that will survive low temperatures help you avoid stresses with late or early frosts.
Hardy annual plants are those which can usually be grown outdoors in most parts of the UK from spring through to autumn without any form of protection. Some are sown in autumn, while others are sown in spring.
It is important to note that hardiness is a range, not an absolute. So while there are many plants commonly described as hardy annuals, the degree to which they can cope with cold temperatures can differ dramatically. The temperatures they can survive at will depend on a range of factors to do with the specific local conditions in your garden.
Which hardy annual plants you should choose will depend on where exactly you live, and the conditions to be found there. And also on when you plan to sow, and why you wish to grow the plants in question.
However, here are 20 hardy annual plants upon which UK gardeners may usually depend:
1. Ammi majus
Ammi majus, bullwort, or common Bishop’s weed has a hardiness rating of H6. This is a great plant for pollinators and other beneficial insects, with delicate umbels of lacy white flowers which bloom from June to August. It can be a great choice for many gardens, working in most soil types as long as they are well drained. These plants are happy in full sun, partial or dappled shade.
2. Agrostemma githago
Agrostemma githago, also known as corncockle, is a pretty annual with funnel-shaped purple flowers 5cm across in summer. It will work well in well-drained sand or loam in a sunny spot, and has a hardiness rating of H5. These flowers are also attractive to bees, and like the above, work well for cut flowers.
3. Calendula officinalis
The tried and tested favourite is a great hardy annual, which works equally well in a mixed flower border, or as a companion plant in your vegetable garden. These flowers will grow best in full sun, but can also cope with partial shade, as long as the medium/soil is well drained. These also have a hardiness rating of H5.
4. Centaurea cyanus
The annual cornflower, Centaurea cyanus, has a hardiness rating of H6. This meadow flower is wonderful for a well drained south or west facing position in full sun. If you have sandy or loamy soil where you live, this could be an excellent hardy annual to consider. The pretty deep blue flowers are a delight of late spring and summer.
5. Clarkia amoena
Also known as Godetia, or ‘farewell to spring’, this is another hardy (H6) annual worth considering. Flowers in summer are lilac or pink, sometimes with white centres. They will thrive in full sun or partial shade, in moist but well-drained loam or sandy soil with an acid pH.
6. Echium vulgare
This is one of my top picks for a wildlife-friendly garden. Echium vulgare is also known as ‘Viper’s bugloss’ and it is one of the hardiest of hardy annuals out there, with a hardiness rating of H7. It will thrive in chalk, sand or loam that is well-drained, in a full sun position. It has an upright growing habit, growing to around 75cm tall, and bears beautiful blue/lilac flowers in early summer.
7. Gypsophila elegans
Also known as annual baby’s breath, this is also a pretty hardy annual flowering plant. It has a hardiness rating of H5. The plant grows to a height of around 60cm and produces elegant sprays of delicate star-shaped, white or pinkish flowers in the summer months. It will thrive in a well drained soil in full sun and is great for cut flowers as well as visual and wildlife appeal in your garden.
8. Helianthus annuus
Typically with a hardiness rating of H5, the common annual sunflower, Helianthus annuus, is another go-to hardy annual for UK gardens. With good reason. No doubt you will already be familiar with the large and dramatic flowers. These are also easy to grow, and provide edible yields for you and potentially for local birds and other wildlife. The sunflower does not just work well in an ornamental border in full sun, with an alkaline or neutral, moist yet well drained soil. It can also be interesting to consider as a companion plant for a vegetable garden.
9. Lavatera trimestris
Hardy through most of the UK (H4), Lavatera trimestris is another interesting hardy annual to consider. It is also sometimes known as annual lavatera or royal mallow. This upright plant grows up to 1.2m in height, and bears open funnel flowers in summer that can be up to 10cm across. Usually, blooms are in shades of pink, or white.
10. Limnanthes douglasii
Better known to some as poached egg plant, Limnanthes douglasii has a hardiness rating of H5. It will do well in most soils, as long as they are moist but well drained, and will prefer a full sun location. This bush-shaped annual takes its name from the appearance of its flowers, which are open to a bowl shape, with yellow in the middle, and white towards the outside.
11. Lunaria annua
Annual honesty, Lunaria annua, is H6 hardy. It bears purple flowers in late spring and early summer followed by attractive silvery seed pods. Though it can sometimes be biennial, it is usually treated as an annual in the UK. It is a good choice for a chalk, sand, or loamy soil that is moist but well drained. And it can cope in either full sun or partial shade. This is another great choice for a wildlife garden.
12. Molluccella laevis
Molluccella laevis, also known as bells of Ireland, is highly prized for flower arranging. It has a hardiness rating of H4. These hardy annuals can grow well in most soils, as long as they are moist but free draining. A sheltered spot in full sun will be ideal. These plants can grow up to almost a metre tall, and bear small white or pale pink flowers in bell-shaped calyx in late summer.
13. Nigella damascena
Nigella damascena, also known as ‘love in a mist’ has a hardiness rating of H3, so is fully hardy in coastal and milder parts of the country. While not quite as hardy as the options mentioned above, it is still classed as a hardy annual, and is a great choice where well drained, full sun and sheltered conditions can be provided. It is another plant that is good for bees and other pollinators, and is a well known stalwart of many cottage gardens. It has pretty blue flowers between July and September.
14. Orlaya grandiflora
This plant, also known as white laceflower, is another option that is great for insects. It bears white flowers in graceful umbels in summer and into autumn. This is another of the hardiest annuals out there, with a hardiness rating of H7. It likes a well drained soil in full sun.
There are a number of different poppies that are great hardy annual plants. Papaver rhoeas, the common poppy, has a hardiness rating of H7. Its fleeting bright red flowers are instantly recognisable, and are found in many wildflower meadows. It will grow in any free draining fertile soil in full sun.
16. Phacelia tanacetifolia
Another top pick for wildlife gardens, and also useful as a cover crop for cultivation areas, Phacelia tanacetifolia (Fiddleneck) is H4 hardy, and is beloved of bees and other beneficial insects. It does well in fertile, well-drained soil in full sun. Like echium vulgare, it is in the Boraginaceae plant family.
17. Phlox drummondii
Annual phlox, phlox drummondii has a hardiness rating of H6. It will grow well in full sun or part shade in a well-drained and fertile soil. These plants have pretty little flowers, in a range of hues, often with prominent eyes, which bloom in spring.
18. Salvia viridis
Painted sage, Salvia viridis, is grown not for its flowers but for its colourful bracts, modified leaves, which are born on upright stems in summer. They come in a range of pink and purplish shades. This plant is rated with a hardiness of H5. It will do best in a sunny and free draining position out of strong winds and can look great below rose bushes.
19. Scabiosa atropurpurea
Scabiosa atropurpurea, annual sweet scabious, is another great hardy annual to consider for your garden. It is an annual (or sometimes short lived perennial) with a hardiness rating of H4. It will grow well in a fertile, well drained alkaline or neutral soil in full sun. And bears beautiful purple flowers followed by bristly seed heads.
20. Tropaeolum majus
The nasturtium is an incredibly useful garden plant. In addition to producing plenty of pretty flowers, it can also be useful as a companion plant in a vegetable garden, and even provides a number of edible yields itself. It has a hardiness rating of H3, but though not quite as capable of surviving low temperatures as most other hardy annuals on this list, it is still well worth considering in many UK gardens.
These are just some of the many interesting hardy annuals to consider for your garden – but should give you an interesting place to start when making annual plant choices for your location.