Osteospermum Year: What to Do Each Season, From Spring Cut to Cuttings

How the year is shaped

Osteospermum runs on a two-peak rhythm rather than a single summer. The heavy flush comes in the cool bright weeks of spring and holds into early summer. Sustained heat then shuts bud production down for a period that may be a few weeks or a couple of months depending on your climate. As nights cool again, the plant comes back into bud and gives a second flush that often carries on until the first hard frosts. Everything you do through the year is either preparing for one of those flushes or managing the gap between them.

Layered on top of that is the plant's habit of building wood. Left alone, it spends each year putting flowers further out on longer bare stems, so an annual hard cut is not optional maintenance but the thing that keeps it worth growing at all. And because even a well-cut plant is at its best young, one cutting session a year keeps a supply of fresh plants coming.

Four jobs, then, carry the whole year: cut hard in spring, deadhead through the first flush, shear by a third as the heat pause starts, and take cuttings in late summer. Do those four and the rest is watering.

Spring: cut back, plant out, pinch

As growth restarts and the worst of the cold has passed, cut established plants back hard. Take them down by a third to a half, always cutting just above a pair of leaves and always leaving leaves below every cut, because this plant reshoots poorly from bare old wood. Remove entirely leafless woody stems at their base rather than shortening them. The aim is a low dense leafy mound with no long naked arms, and the plant will look bad for a fortnight before it looks much better than it would have.

Harden off overwintered cuttings and any bought plants over seven to ten days, then plant out after the last frost once nights are reliably above about 45F (7C). Space them twelve to eighteen inches (30 to 45 cm) apart, set the crown level with or slightly above the soil surface, water in once and then let the surface dry before watering again.

Pinch the tips out of every young plant about two weeks after planting, taking an inch (2.5 cm) off each shoot. Give one light balanced feed as growth accelerates and then leave the feeding alone. Start checking shoot tips and unopened buds for aphids now, because soft spring growth is exactly what they colonise first.

Early summer into the heat: deadhead, then shear

The main flush is a deadheading job. Go over the plants every few days, snipping each spent flower off with its stem back to the first pair of leaves rather than beheading it. This keeps buds coming and stops the plant putting energy into seed. Water deeply and infrequently, and feed lightly every two to three weeks if the plants are in containers, using something high in potash rather than a general feed.

When the flush visibly slows and the weather turns hot, do not wait and hope. Shear the whole plant back by about a third, keeping leaves below every cut. This is the job that decides how good your autumn is: a plant that goes into the heat as a dense mound with fresh shoot tips comes out of it covered in buds, while one left sprawling comes out of it sprawling.

Through the hot weeks, keep plants watered so they do not check, stop feeding nitrogen, and accept that nothing will flower. Watch for downy mildew in humid spells, water at the base in the morning, and thin any congested growth so air moves through the plant.

The summer pause is normal. Foliage that stays green and healthy while no buds appear is a plant waiting for cooler nights, not a plant that needs feeding, moving or watering more.

Late summer to first frost: cuttings and the second flush

Late summer is the most important date in the osteospermum year, because it is when cuttings root best. Take three to four inch (8 to 10 cm) non-flowering shoot tips while the weather is still warm, insert them into a gritty half-and-half mix, and keep them covered, bright and out of direct sun at around 65 to 70F (18 to 21C). They root in two to three weeks. Take more than you need; they are free and winter losses are normal.

As nights cool, the second flush arrives. Resume deadheading and light feeding, and enjoy it, because it often runs longer than the spring one and comes when little else is at its best. Do not cut the plant back now; new growth forced late is soft, will not flower before the cold, and rots readily.

As the first frosts approach, stop feeding. Osteospermum takes a light frost but is stopped by a hard one, and in cold areas the parent plant may not survive winter outdoors at all. Your insurance is the tray of rooted cuttings, which is why late summer matters more than any autumn protection you might rig up.

Winter, and a record worth keeping

Winter is a holding operation. Rooted cuttings sit somewhere bright, frost-free and airy at 40 to 50F (5 to 10C), barely watered and not fed. Check them every week or two, remove yellowing leaves before they rot, and pull out anything that goes soft at the base along with its compost. In mild areas an established plant left outside may come through, particularly in a raised, sharply drained spot; in wet cold ground it will rot rather than freeze, so drainage is the deciding factor.

Keep a short dated log through the year and it will make every one of these decisions easier next season. The dates worth having are: the spring cut, planting out, first flower, the day flowering stopped in the heat, the mid-season shear, the day buds returned, the day you took cuttings and how many, the last flower, and the first frost.

After two seasons those dates stop being general advice and become your garden's actual calendar. You will know how many weeks after the mid-season shear your plants reflower, so you can time it to hit the cool weather. You will know your real strike rate on cuttings, so you can take the right number. And you will stop worrying in high summer, because the log will show you that the same thing happened last year and that flowers came back on schedule.