Tuberous Begonias in Canada
Start dates by city, the shade they want, and how to keep the tubers from year to year.
Tuberous begonias in Canada are grown as summer plants and kept as tubers over winter. NC State rates them hardy only in US Zones 9 to 11, so in Canada the tubers come indoors before frost.
They flower for about four months, from early summer until the first fall frost, according to the same source, which makes them one of the longest-blooming plants for a shady bed or basket.
Tuberous begonias at a glance: Start tubers indoors 2.5 to 3 months before your last frost, planted shallowly, hollow side up. Move them outside after the last frost into partial or dappled shade, with rich, moist, well-drained soil. Taper watering as leaves yellow in fall, then lift and store the tubers dry and frost-free.
Planting a shady basket? See Growing Fuchsia in Canada for the other classic shade basket plant.
Start Dates by City
NC State says to start plants indoors about 2.5 to 3 months before the danger of frost is over. Counted back from this site’s average last frost dates:
| City | Start Indoors (about 3 months) | Latest Start (about 2.5 months) | Average Last Frost |
|---|---|---|---|
| Calgary | Feb 22 | Mar 9 | May 23 |
| Edmonton | Feb 13 | Feb 28 | May 14 |
| Saskatoon | Feb 24 | Mar 11 | May 25 |
| Winnipeg | Feb 24 | Mar 11 | May 25 |
| Thunder Bay | Feb 27 | Mar 14 | May 28 |
| Ottawa | Feb 8 | Feb 23 | May 9 |
| Toronto | Jan 20 | Feb 4 | Apr 20 |
| Montréal | Feb 8 | Feb 23 | May 9 |
| Quebec City | Feb 16 | Mar 3 | May 17 |
| Halifax | Feb 9 | Feb 24 | May 10 |
| St. John’s | Feb 23 | Mar 10 | May 24 |
Dates are counted back from the average last spring frost. On the BC coast the last frost comes so early that the count falls in December; NC State’s advice is to start in late winter, so start there in late January or February.
Planting and Light
NC State: plant tubers shallowly with the concave (hollow) side up, three or four to a container or 30 to 45 cm (12 to 18 inches) apart in the ground. They prefer partial to dappled shade and organically rich, moist, well-drained soil, tolerate early morning and late afternoon sun, and are not drought tolerant. Give them good air circulation and shelter from too much sun and wind.
Through the Summer
The same source recommends regular feeding during the growing season for the most flowers, removing spent flowers and leaves, and taking care not to injure the tuber if staking.
Storing the Tubers
NC State says to taper off watering in fall as the leaves turn yellow, and before the first fall frost either move containers to a frost-free place or dig up the tubers. Store them dry over winter and replant in late winter.
NC State lists tuberous begonias as toxic if eaten, with the roots the most toxic part, and notes the sap can irritate skin. Keep the tubers away from pets.
Frequently Asked Questions
When should I start tuberous begonias indoors?
About 2.5 to 3 months before your last spring frost, according to NC State.
Which way up do begonia tubers go?
Concave (hollow) side up, planted shallowly.
Do tuberous begonias like sun or shade?
Partial to dappled shade. NC State says they tolerate early morning and late afternoon sun but need protection from too much sun and wind.
Can tuberous begonias survive a Canadian winter outside?
No. NC State rates them hardy only in US Zones 9 to 11, so lift and store the tubers before frost.
How do I store begonia tubers over winter?
Taper watering as the leaves yellow in fall, then dig the tubers before frost and store them dry in a frost-free place until late winter.
Are tuberous begonias toxic to pets?
NC State lists them as toxic if eaten, with the roots the most toxic part.
Sources
- North Carolina State University Extension Gardener Plant Toolbox — Begonia (tuberous types)
- Environment and Climate Change Canada — Canadian Climate Normals (the frost dates in the tables, read from this site’s frost data)