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As always to this type of question about annual vs perennial, the answer is complicated. Osteospermums are generally tender or half-hardy perennial plants which makes their survival in UK winters perilous. However, many of the different cultivars and hybrids (there are around 900 officially recognised ones) were developed to be annual plants, dying at the end of the growing season. But two osteospermum varieties, in particular, are labelled as hardy, and these have the best chance of being perennials if you over-winter them correctly.
What are osteospermums?
Osteospermums are daisy-like plants that usually grow between 30cm and 90cm high, and 30cm to 60cm wide. They’re also known as African daisies for their bright appearance and large, showy flowers in vibrant colours. Many species of osteospermums have one flower per stem, but gardeners have developed cultivars with semi-double and double blooms for even more riotous colour.
Are osteospermums perennial?
We hate to say this, but it depends. Originally half-hardy or tender perennial flowers, osteospermums have been mixed and matched with those of different varieties and species to create new cultivars that look great in flower beds and borders. This genetic manipulation through natural means has turned most osteospermum cultivars into purely annual plants. Most people use these plants as summer bedding plants, planting them after the last frost in spring (usually around May).
So, it’s best to treat osteospermums as annuals now. However, two varieties are identified as being hardy and are worth trying out as perennials. Of course, whether they’re really perennials in all parts of the UK depends on whether they survive the winter.
In general, osteospermums that have a toothed edge to their leaves and grow in clumps are hardier than other types.
What are the perennial osteospermum varieties?
This osteospermum is classified as a shrub because it’s a perennial. It grows up to 30cm tall and some varieties of it spread out as well. The green-grey leaves have a slight scent and grow up to 10cm long, in oblong, oval or lance shapes. Some or all of the edges of the leaves have a zig-zag indentation along them. The centre of the 5cm to 8cm diameter flower are usually purple and the starburst petals are white on top and purple underneath. This is a very attractive flower to have return every year.
O. Jucundum is a bushy perennial that flowers from late spring to autumn, so be sure to plant it early for its first year. The daisy-like flowers are 6cm in diameter and are generally a deep pink which contrasts well with the bright yellow centre of the bloom. The leaves are narrow and work well as a visual backdrop to the flowers. Another variety, Merriments Joy, has pinkish-purple flowers.
How to look after perennial osteospermums
Pruning your osteospermum is optional but deadheading is mandatory to ensure prolonged blooming. As soon as a flower wilts, cut it off just above the set of leaves below it on the stem. This lets the plant use all its energy for new growth and development.
Prune your perennial osteospermum in the spring to remove the old growth that you left there in the winter to protect it. In the summer, consider pruning some of the older stems by 1/3 to ½ their length. This spurts the foliage into new growth and keeps the plant looking neat and tidy.
How to overwinter perennial osteospermums
Make sure you shelter your plants from the cold, wind and frost in late autumn and winter. Consider covering them with open-ended cloches with a light fabric across the end, but be sure not to position the open ends in the direction of the wind. Use organic mulch around them that will act as a blanket as well as deliver much-needed nutrients to the plant in the spring.
If your part of the world gets very cold winters, your best bet to overwinter your osteospermum is to take a rooted cutting of it, put it in a pot and bring it indoors for the cold season. Treat the rest of the plant as an annual; that is, let it die. Plant the cutting back in your garden in the spring after any threat of frost has passed.
The only way to really know if your osteospermum can handle being a perennial is to see if it’s still alive in spring.