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Osteospermum is very colourful flowers that are perfect for border gardens or patios and are usually planted as a summer bedding plant in the UK although you can get some hardy perennial varieties but most people plant summer bedding types. They take on a daisy-like shape with colourful flowers with contrasting centres which you will enjoy from the end of spring all the way through the first frost if they are deadheaded regularly. These are very easy to grow and even easier to propagate from cuttings but some varieties can also been grown from seed.
Given the size though, they are suitable for the front or middle of a colourful border garden, depending on what else you have. Many gardeners plant them as an effective ground cover too. However, they are half-hardy generally and given that they are not really classed as hardy, they need to be planted about when the risk of frosted has passed which is usually around May for most parts of the UK.
Planting osteospermum – plant out in May
The best time of the year to plant osteospermum is May after all likelihood of frost is gone as already mentioned. They can usually handle a light frost should they get caught out with a late frost.
Use a good quality multi-purpose compost
If you purchased plants from a nursery you want to plant them in your garden or in a container as soon as possible. Make sure to dig a hole that is twice the size of the root ball width and then make the plant level with the soil so that it’s at the same depth that was in the container. Compost wise they like a fertile soil but are not too fussy, a good quality multi-purpose compost is perfect.
If you are planting something you have grown from cuttings, we recommend pinching out the tops to encourage busher plants and growing them in 9cm pots before planting out to ensure they have a good root system.
Caring for Osteospermum
Plant in a sunny position
As mentioned these are very easy plants to care for and they will spread quickly giving you the perfect ground cover if you so choose. They prefer to be in a sunny position. Because they are a flowering plant, as is the case with most flowering plants, full sun will give them the best floriferous qualities but they will tolerate partial shade in exchange for fewer flowers but they really do produce the best show in full sun.
Plant in moderately fertile well-drained soil
In terms of soil, make sure you have free-draining soil. If you are putting them in containers just make sure you have a lot of drainage holes at the bottom. The last thing you want is for them to get waterlogged. Most plastic containers can be easily drilled at the bottom to add more drainage. If you have very heavy soil in your garden you can always add things like grit or compost to try and loosen it up and bulk it out a little and break the soil up.
Water regularly until well rooted
They tolerate dry conditions quite well once established but you do need to water them for the first few weeks after you plant them until they are well rooted and then subsequently once per week during warm periods or when the first couple of inches of soil becomes dry.
Water regularly when grown in containers
If you are growing them in containers be sure to water them regularly enough that they never completely dry out. If they completely dry out either in containers or in the ground it can cause the buds to fall or not open.
During the growing season, as with most summer plants, you can promote flowering by feeding every 2 weeks which is particularly important if you have planted your osteospermum in containers.
Deadhead regularly to prolong flowering
Other than deadheading the plants regularly to prolong flowering and cutting back any dead stems, there is next to no maintenance required. If you have grown your osteospermum in pots, once the root ball gets a little congested you’ll have to repot them in something that’s slightly larger and, again, has adequate drainage holes.
If you are planting a one of the few hardier varieties you can cut it back to about 10cm in height at the beginning of Spring right before any new growth manifests. Removing the old foliage in this fashion will encourage the plant to focus on new development.
Most osteospermum are actually hybrids so you can’t propagate them well from seed. If you don’t have any preference for what types of plants are what colours you get you can just scatter the seeds from your existing plants on top of a seed tray, and place them in a light warm place to germinate and then pricking out into small 9cm pots and growing them on. However, for most varieties, growing from seed is not as reliable as taking cuttings from a plant if you want to propagate the same plant to get the same colours.
Taking cuttings will help the semi-hardy varieties to propagate more effectively during the wintertime. This is a process you want to start at the end of summer or the beginning of autumn. The cuttings should be grown in module trays or 7cm square pots or 9cm round.
As when taking most cutting, you should cut a non-flowering shoot from your osteospermum plant that is around 5cm in length.
Remove all of the lower leaves, dip the base of the stem into rooting hormone powder, and place them in the containers or plug trays.
You can place them in a windowsill that’s out of direct sunlight, in a propagator, or a heated Greenhouse. Much the same as any other plant, make sure they don’t dry out and avoid over-watering. Grow them over winter before planting out in spring when the risk of frost has passed.
Pests and Problems
These are generally easy plants in terms of pests and diseases but they can be attacked by aphids. Aphids will cause the leaves to curl and yellow and if left untreated eventually the stems will die off.
It’s important to remove the aphids as soon as you see them either by pinching them off, spraying them away with a strong jet of water or spraying the plant with a soap solution. Introducing beneficial predators like ladybugs and yes you can actually buy these online. If the problem is particularly bad you can spray with a pesticide bug killer.
In terms of diseases, powdery mildew is all that you really have to look out for. If you noticed white powdery patches of mildew on the leaves, especially during hot weather when there isn’t enough air circulation, you can remove any weeds around the area, avoid over-watering, remove the affected leaves, increase air circulation to try and help prevent it. You can also consider spraying with a fungicide if you have badly affected plants.