Ornamental allium · Pretoria, Gauteng, South Africa
When to sow ornamental alliums in Pretoria
Main outdoor window
30 Apr - 14 May
The window this page is built around.
Timed from last spring frost
24 July
In Pretoria, on your chosen risk.
Ready to pick
29 Oct - 28 Dec
If you plant at the start of the window.
The average last frost. Half of all years are later than this.
Step by step in Pretoria
Each window is a range, not a single day. Earlier in the range buys you a longer season; later in it buys you a safer one.
Plant the bulbs
30 Apr - 14 May
Four to six weeks before your first frost, so roots form before the ground cools.
In flower
29 Oct - 28 Dec
Ornamental alliums through the year
Against the frost risk in Pretoria
Why these dates
Plant in mid-autumn, four to six weeks before the first frost, at three times the bulb's height. Site them behind something bushy: the leaves collapse into an untidy heap while the flower is still at its best, and need hiding rather than removing.
Hardy to -30C. Needs a cold winter and, more than most bulbs, sharp drainage - alliums rot in a wet winter far more readily than they freeze in a cold one.
Ornamental alliums are anchored to the first autumn frost rather than the last spring one, so the planting window on this page counts backwards from the end of the season in Pretoria instead of forwards from its start.
Pretoria sits in zone 10a, which is milder than this crop wants, and a winter that never really arrives is its own problem. The dates below still describe the right time of year; the open question is survival rather than timing.
The median frost-free season here is 322 days, against 180 to 230 days to first flower for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.
Also in Pretoria
Other flowers to time
Growing ornamental alliums in Pretoria
When should I plant ornamental alliums in Pretoria?
Aim for 30 Apr - 14 May in an average year. If you would rather not gamble on the weather, wait until 15-29 Apr - by then frost has finished in nine years out of ten.
When will ornamental alliums be ready to harvest in Pretoria?
Expect to start picking around 29 Oct - 28 Dec, based on 180 to 230 days to maturity from the planting date calculated for this location.
How much frost will ornamental alliums tolerate?
Hardy to -30C. Needs a cold winter and, more than most bulbs, sharp drainage - alliums rot in a wet winter far more readily than they freeze in a cold one.