Zone 5 Begonias: Start Tubers Indoors by Late March for Full-Season Blooms
Zone 5 gives begonias 140–155 frost-free days. Start tuberous begonias 8–10 weeks indoors and you get flowers from mid-June. Wait and plant outdoors — you get 6 weeks of bloom. Iowa State Extension timing, variety table, and overwintering steps.
Zone 5 gives you roughly 140–155 frost-free days, depending on your city. A tuberous begonia takes 12–14 weeks from a dormant tuber to its first flower. Do that math and you’ll see why zone 5 gardeners who plant directly outdoors after the last frost are getting 6 weeks of bloom — if they’re lucky — before September’s first chill ends the season.
The fix is simple: start tubers indoors 8–10 weeks before your last frost date, per Iowa State University Extension. In zone 5, that means mid-February through late March. You’ll have flowers from mid-June and color running through mid-October — over 14 weeks of display from the same plant. This guide covers which begonia type suits your situation, exact start dates by zone 5 city, the fastest-blooming varieties, and how to store tubers so the same plant performs for years.
Three Begonia Types for Zone 5 — Which One Suits You?
Understanding which begonia you’re growing changes everything about timing and care. Zone 5 gardeners have three realistic options, each with different demands.
Tuberous Begonias (Begonia × tuberhybrida)
The showiest type, with 2–4-inch double flowers in shades from cream and blush to deep scarlet and orange. Tuberous begonias grow from a fleshy tuber that must be started indoors in late winter, moved outdoors after last frost, and dug before the first killing frost each fall for indoor storage. The same tuber, properly stored, will bloom reliably for many years. These are the most time-intensive option but produce the most dramatic display — the right choice if you want statement containers or a border that stops visitors in their tracks.
One important note from University of Minnesota Extension: unlike potato tubers, begonia tubers cannot be cut into sections to multiply them. Each tuber must be planted whole.
Wax Begonias (Begonia × semperflorens-cultorum)
The lowest-maintenance option. Wax begonias are fibrous-rooted annuals that bloom continuously from planting to frost in zone 5, need no overwintering, and tolerate both sun and shade. Bronze-leaved varieties handle more direct sun than green-leaved types, which prefer morning sun with afternoon shade. The trade-off is flower size — wax begonias produce small, simple blooms, nothing like the rose-form doubles of tuberous types. But they fill a border or container with reliable, unfussy color from late May to first frost, and they’re inexpensive enough to replant every year without guilt.
Hardy Begonia (Begonia grandis)
The only begonia with true perennial potential — but zone 5 sits at the edge of its range. NC State Extension rates B. grandis as hardy in zones 6a–9b, and Missouri Botanical Garden notes that even in zone 6–7, heavy winter mulch is “advisable” because plants are “not reliably winter hardy” without it. In zone 5, sheltered spots — a south-facing bed against a brick wall, or an urban garden with significant heat retention — give this species its best chance with 3–4 inches of mulch applied after the foliage dies back in fall.
If it does survive, B. grandis offers a distinctive bonus: it produces tiny bulbils in its leaf axils in late summer that fall naturally and sprout the following year, so one plant gradually spreads into a small colony over several seasons. Pale pink flowers appear July through October. Treat it as a pleasant surprise if it overwinters and a beautiful annual if it doesn’t.
For a full breakdown of begonia species and how to identify which type you have, see our begonia growing guide covering tuberous, fibrous, and rex types.
Zone 5 Begonia Planting Calendar
Work backward from your last frost date. Average dates for common zone 5 cities, with Iowa State University Extension’s 8–10 week indoor start rule applied:
| City | Avg Last Frost | Start Tubers Indoors | Transplant Outdoors |
|---|---|---|---|
| Chicago, IL | April 18 | February 7–18 | After May 2 |
| Des Moines, IA | April 23 | February 12–23 | After May 7 |
| Springfield, IL | April 23 | February 12–23 | After May 7 |
| Indianapolis, IN | April 25 | February 14–25 | After May 9 |
| Cedar Rapids, IA | April 30 | February 19–28 | After May 14 |
| Fort Wayne, IN | May 1 | February 19–March 1 | After May 15 |
Transplant outdoors once nights stay consistently above 50°F — not just after the last frost date. Tuberous begonias are sensitive to cold soil and cold nights even when no actual frost is forecast.
Month-by-Month Tasks
January: Order tubers now. Premium named cultivars (Nonstop® series, Illumination® series) sell out by mid-February online. Choose firm tubers with no soft spots or visible mold.
Mid-February to late March: Start tubers indoors (see steps below). Earlier start = earlier blooms; earlier blooms = more weeks of display in your short zone 5 season.
April: Keep plants growing under bright indoor light. Begin hardening off 2 weeks before your last frost date — move pots to a sheltered outdoor location during warm afternoons, bring back inside before temperatures drop below 50°F at night.
Late April to mid-May: Transplant outdoors once nighttime temperatures are reliably above 50°F. Plant wax begonias from transplants in the same window.
September: Watch the forecast. At the first hard frost warning, dig tuberous begonias immediately. Wax begonias can be potted up and brought indoors as houseplants if you want to try carrying them over.
How to Start Tuberous Begonias Indoors
Following Iowa State University Extension’s method:
- Fill a shallow tray or pot with moist, well-drained potting mix. Do not use garden soil — it compacts and harbors pathogens at indoor temperatures.
- Orient tubers concave-side up. The hollowed, bowl-shaped surface is where the growth eyes are located. Place each tuber so this depression faces upward.
- Cover with ½ to 1 inch of potting mix. Deeper burial delays sprouting.
- Set containers in a warm spot at 70°F. A heat mat designed for seed-starting works well. Cold windowsills — common in zone 5 winters — slow germination significantly.
- Keep the mix evenly moist but not wet. Soggy medium rots tubers before they can sprout. If you’re unsure, err slightly dry.
- Move to bright indirect light once sprouts appear — usually 4–6 weeks after planting.
- Begin feeding with a dilute balanced fertilizer every 2–3 weeks once plants are 3 inches tall.
Best Varieties for Zone 5’s Short Season
Not all tuberous begonias reach peak bloom at the same speed. For zone 5, prioritize compact varieties in the Nonstop® series — they’re bred for continuous, early blooming, which is exactly what a 140-day season demands.
| Variety | Type | Best Use | Zone 5 Advantage |
|---|---|---|---|
| Nonstop® series | Tuberous | Beds, containers | Compact, earliest to bloom in tuberous group; named for continuous display |
| Nonstop® Mocca Scarlet | Tuberous | Containers | Chocolate foliage with deep red blooms; heat-tolerant for summer spells |
| Illumination® Apricot Shades | Tuberous (trailing) | Hanging baskets | Trailing stems; start 2 weeks earlier than upright types for July display |
| Dragon Wing® Red | Fibrous (wax-type) | Beds, large containers | Very vigorous; one plant fills a large pot by midsummer; no tuber storage needed |
| BabyWing® Pink | Fibrous (wax-type) | Edging, small containers | Compact and sun-tolerant; plant after last frost, done for season — no storage |
The Nonstop® series earns its name in zone 5 conditions: start tubers in late February, transplant in late May, and you’ll have flowers from mid-June through first frost — that’s roughly 16 weeks of color from a zone 5 growing season. Illumination® trailing types take slightly longer to fill out; start them a week or two earlier and plan their display around hanging baskets and tall container arrangements.
Soil, Light, Water, and Fertilizer
Soil
Both tuberous and wax begonias need well-drained soil with plenty of organic matter, at a pH of 5.5–6.5. Heavy clay soil is the most common killer of tuberous begonias in zone 5. The mechanism: waterlogged clay creates anaerobic conditions around tubers, which allows oxygen-deprived pathogenic fungi to proliferate. A simple fix is working 2–3 inches of compost into your planting area before setting out transplants. In containers, use a quality potting mix rather than garden soil — the structure holds up through an entire growing season of regular watering.
Light
Tuberous begonias need protection from midday and afternoon sun. Morning sun before 10 a.m. is fine; overhead summer sun bleaches petals and causes petal drop. Even in zone 5, where summer sun intensity is lower than in the South, direct afternoon exposure stresses tuberous begonias noticeably. North-facing and east-facing beds work well. In zone 5, begonias labeled for “partial shade” can often succeed in positions with slightly more sun than they’d tolerate in warmer zones — but afternoon shade still protects their large, soft leaves from scorching.
Wax begonias are more forgiving. Bronze-leaved varieties handle nearly full sun; green-leaved types do best with morning sun and light afternoon shade.
Water
Keep soil consistently moist but never waterlogged. Water at the base, not over the foliage — wet leaves in warm, humid weather invite botrytis (gray mold), particularly a risk for tuberous begonias with their large petals. Clemson Cooperative Extension recommends drip irrigation or early morning overhead watering to reduce fungal disease pressure. Container-grown begonias need watering more often than in-ground plants, especially during zone 5’s July and August heat spells.
Fertilizer
University of Minnesota Extension describes tuberous begonias as “fairly heavy feeders.” Apply a dilute balanced fertilizer every 2 weeks for containers (where nutrients leach with watering) and every 3–4 weeks in garden beds. Once the plant is well-established and flowering freely, consider switching to a formula lower in nitrogen — excess nitrogen pushes leafy growth at the expense of blooms.
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→ View My Garden CalendarOverwintering Tuberous Begonias in Zone 5
Tuberous begonias will not survive zone 5 winters in the ground — temperatures drop well below the freezing point that kills tuber tissue. Dig them each fall and you get the same plant back year after year, often with a larger tuber that produces even more blooms the following season.
When to Dig
Dig within a few days of the first killing frost, according to Iowa State University Extension. Don’t delay — repeated freezing damages tuber cells and reduces next year’s vigor. Watch fall forecasts carefully; zone 5 first frosts often arrive in late September or early October. For a zone 5 fall gardening checklist, our October zone 5 tasks guide covers the full sequence for closing out the growing season.
Preparing and Curing
- Cut stems 1 inch above the tuber — don’t pull them off, as torn tissue is an entry point for rot.
- Brush off loose soil gently. Don’t wash tubers — wet surfaces entering storage invite mold.
- Spread tubers in a single layer in a cool, dry spot with good airflow for 2–3 weeks to cure. A garage shelf or basement workbench works well in October.
Storage
Place cured tubers in a cardboard box or wooden crate filled with peat moss, vermiculite, or dry sawdust. The medium matters: without it, tubers dry out and shrivel; packed directly in a plastic bag, they stay too moist and rot. Store at 40–50°F.
That temperature window is precise for a reason. Below 40°F, ice crystals form inside tuber cells — the damage is invisible until spring, when a tuber that looked fine simply fails to sprout. Above 50°F, tubers break dormancy prematurely, sending up pale, weak shoots in the dark that exhaust the tuber’s energy before planting time arrives. An unheated basement that stays around 45°F, a three-season porch, or a spare refrigerator set to 45°F are all reliable options for zone 5 storage.
Check tubers every 4–6 weeks through winter. A soft, dark patch indicates rot — cut it away with a clean knife and dust the wound with sulfur powder if the tuber core is still firm and white. Discard tubers that are more than half compromised.
If you enjoy other low-maintenance perennials for zone 5 shade, astilbe is a reliable companion plant for the same cool, shaded beds where begonias thrive — with none of the fall digging.
Frequently Asked Questions
Can begonias survive winter outdoors in zone 5?
Tuberous begonias and wax begonias cannot. Tuberous types must be dug and stored indoors each fall; wax begonias are annuals in zone 5 and die at first frost. Hardy begonia (B. grandis) is rated zones 6a–9b and may survive zone 5 winters in sheltered, heavily mulched locations, but this is not guaranteed.
Can I direct-plant begonias outdoors in zone 5 without starting indoors?
Wax begonias — yes, plant transplants outdoors after last frost. Tuberous begonias — not recommended. Planted outdoors after your May 1 last frost, tuberous begonias won’t bloom until late July, leaving just 6–8 weeks before September frosts arrive. Starting indoors in February or March gives you 14+ weeks of display.
When is it too late to start begonia tubers in zone 5?
If you’re still within 6 weeks of your last frost date, start them — late blooms are better than none, and established tubers store better in fall than weak ones. Below 6 weeks before last frost, you risk not seeing flowers at all before the season ends.
Do wax begonias come back every year in zone 5?
No — they’re frost-tender and will die at first frost outdoors. You can pot up wax begonias in fall and overwinter them as houseplants, then return them outdoors next spring, but this is more trouble than starting fresh from transplants.
Sources
- Tuberous Begonias — University of Minnesota Extension
- When Should I Start Tuberous Begonias Indoors? — Iowa State University Extension
- How Do I Overwinter Tuberous Begonias? — Iowa State University Extension
- Begonia grandis (Hardy Begonia) — NC State Extension Gardener Plant Toolbox
- Begonia — Clemson Cooperative Extension HGIC 1159
- Begonia grandis — Missouri Botanical Garden Plant Finder
- Tuberous Begonias: A Growing & Care Guide — Garden Design
