Few plants reward Bay Area gardeners as generously as begonias. With their jewel-toned blooms, architectural foliage, and genuine adaptability to our foggy mornings and warm afternoons, begonias have earned a permanent place in San Jose gardens. Whether you’re growing them in a shaded patio container or tucked under the canopy of a valley oak, success comes down to timing — knowing what your plants need month by month, season by season.
This calendar is written specifically for gardeners in USDA hardiness zones 9b–10a, the climate band that covers most of Santa Clara County. Our mild winters, dry summers, and marine-influenced springs create both opportunities and quirks that standard begonia guides from the Midwest or Pacific Northwest simply don’t address.
Know Your Begonias: A Quick Bay Area Type Overview
Before diving into the calendar, it helps to know which category your begonia falls into. The three types most commonly grown in Bay Area gardens each have distinct needs:
Tuberous begonias (Begonia × tuberhybrida) are the showboats — large double blooms in vivid reds, oranges, pinks, and whites. They grow from corms that must be dug and stored in cold-winter climates, though in zones 9b–10a, we have more flexibility. They bloom summer through fall and strongly prefer cool mornings and filtered light.
Fibrous (wax) begonias (Begonia × semperflorens-cultorum) are the workhorses of San Jose bedding displays. Compact, heat-tolerant, and nearly everblooming, these are the ones you’ll find at every Home Depot in March. They thrive in both sun and shade depending on the cultivar and are essentially low-maintenance once established.
Rex and cane begonias (including angel-wing types) are grown primarily for their spectacular foliage — swirling patterns of silver, burgundy, chocolate, and lime. They flourish in our humidity-variable climate with a little attention to airflow, making them excellent houseplant-to-patio transitions. The American Begonia Society notes that cane types, especially, perform exceptionally well in California’s coastal influence zones.
Month-by-Month Begonia Care Calendar (San Jose, Zones 9b–10a)
January – February: Tuberous begonias are dormant in storage; check corms monthly for rot or excessive desiccation. Fibrous and rex types grown indoors or under eaves benefit from reduced watering. This is an ideal time to review last season’s notes, order new cultivars from specialty catalogs, and amend container soil with fresh compost.
March: Soil temperatures creep toward 60°F (15°C) — the signal to start tuberous begonia corms indoors under grow lights. UC Cooperative Extension recommends starting them 6–8 weeks before your intended outdoor plant-out date. Begin fertilizing overwintered fibrous begonias with a half-strength balanced fertilizer.
April: After our last average frost date (typically mid-February in San Jose, but cold snaps can surprise us into early April), transition tuberous begonias outdoors gradually. Harden them off over 7–10 days. Plant fibrous begonias in beds and containers once nighttime temperatures reliably stay above 50°F.
May: Full outdoor season begins. Pinch fibrous begonias to encourage bushy growth. Stake tall tuberous varieties before they need it — a proactive step that prevents snapped stems once the heavy blooms arrive. Begin a monthly deep-watering and fertilizing rhythm.
June – August: Peak bloom season. Apply a low-nitrogen, high-phosphorus fertilizer (such as 5-10-10) every two to three weeks to tuberous and cane types to sustain flowering. Watch for powdery mildew as summer fog lingers into mornings — increase airflow around plants as needed. Deadhead spent blooms weekly.
September – October: Begin tapering water and fertilizer for tuberous types. This signals the corms to begin storing energy. In San Jose’s warm falls, tuberous begonias often continue blooming into October; enjoy it, but don’t push them with heavy feeding. Rex and cane types transition beautifully indoors as temperatures start dropping after dark.
November – December: Lift tuberous begonia corms after foliage yellows and stems loosen. Cure them in a dry, shaded spot for two weeks, then store in peat moss or vermiculite at 45–55°F (7–13°C). A cool garage or interior closet typically works well in San Jose. Fibrous begonias may overwinter in sheltered microclimates against south-facing walls — worth attempting in zone 10a.
Watering Schedule: Getting the Balance Right
Begonias are famously unforgiving of both overwatering and drought. The golden rule: water deeply, then wait until the top inch of soil is dry before watering again. For container-grown plants during San Jose’s dry summers (May through October), that often means every two to three days.
The Bay Area’s dry summers demand consistency. Invest in a moisture meter if you’re unsure — it removes the guesswork entirely. According to UC ANR guidelines, begonias in containers need excellent drainage above all else; sitting in waterlogged soil for even 24 hours can invite Pythium root rot. Use a lightweight, perlite-enriched potting mix and ensure drainage holes are never blocked.
In-ground plants rely more on natural rainfall in our wet season (November–April) and may need supplemental drip irrigation in summer. Avoid overhead watering whenever possible; wet foliage in humid morning conditions is an invitation for fungal disease.
Light and Humidity: The Bay Area Advantage
Our climate offers a genuine advantage for begonia growers: the marine layer provides diffuse light and natural humidity that begonias adore. Most types prefer bright, indirect light — the dappled shade under a patio cover or the east-facing side of a fence is ideal.
Tuberous begonias specifically struggle with intense afternoon sun above 90°F; our coastal-influenced summers keep most of Santa Clara County in the 75–88°F range through July, which is close to perfect. Direct morning sun with afternoon shade is the sweet spot.
Rex and cane begonias thrive in 50–60% relative humidity. While our summers are dry, grouping container plants together, using pebble trays with water, or situating them near a drip-irrigated bed can maintain adequate moisture in the air around their leaves.
Propagation Methods for Bay Area Gardeners
Begonias are surprisingly generous when it comes to propagation. The three most reliable methods for home gardeners:
Stem cuttings work for fibrous, cane, and rex types. Take 3–4 inch cuttings just below a leaf node in late spring or early summer, remove lower leaves, and root in moist perlite or a peat-perlite mix. In San Jose’s warm May–June temperatures, cuttings typically root within 2–3 weeks.
Leaf cuttings are the classic method for rex begonias. Slice a healthy mature leaf into 2-inch squares, each containing a visible vein, and press them lightly onto moist propagating mix. New plantlets emerge at the vein intersections within 3–5 weeks.
Corm division for tuberous types: when you inspect stored corms in late winter, any corm showing multiple well-developed eyes can be cut into sections (each with at least one eye) using a clean, sharp knife. Dust cuts with sulfur powder, allow to callous for 24 hours, then start in barely moist medium.
Common Pests and Diseases to Watch For
Bay Area begonias face a predictable set of challenges. Vigilance and early intervention keep most problems minor.
Powdery mildew is the number-one fungal issue, especially for tuberous types during foggy summer mornings. Improve air circulation, avoid wetting foliage, and apply a diluted neem oil spray (2 tsp neem + ½ tsp dish soap per quart of water) at the first sign of the white, dusty coating.
Mealybugs cluster in leaf axils and at stem bases, excreting sticky honeydew. A cotton swab dipped in isopropyl alcohol handles minor infestations; insecticidal soap spray works for larger ones. Check new nursery transplants carefully before introducing them to your garden.
Thrips and spider mites spike during hot, dry spells — exactly the kind of heat events that push inland San Jose into the 95°F+ range in August. A strong water spray dislodges mites; introduce Phytoseiulus persimilis predatory mites as a biological control for serious infestations, available from several Bay Area organic garden suppliers.
Root rot (Pythium, Phytophthora) is almost always a watering or drainage problem. Prevention is far easier than treatment: use well-draining mix, avoid saucers that collect standing water, and never plant in heavy clay without significant amendment.
Overwintering Tuberous Begonias in California
Here’s where Bay Area gardeners have a meaningful advantage over most of the country: our mild winters allow more flexibility in how — and whether — we store tuberous begonias.
In zone 10a (downtown San Jose, Willow Glen, Almaden Valley), tuberous begonias planted in sheltered in-ground beds with good drainage may survive mild winters with minimal protection. A 3-inch layer of mulch over the root zone and a floating row cover on forecast frost nights (we average only 1–3 frost nights per year) is often sufficient.
In zone 9b (foothill edges, Evergreen district, areas closer to the South Bay hills), digging and storing corms remains the safer bet. Lift after the first sign of yellowing foliage, cure in open air out of direct sun for 10–14 days, then pack loosely in dry peat, vermiculite, or shredded newspaper. Store at 45–55°F — a cool interior closet, garage shelf away from the door, or even under a workbench typically maintains this range through our short winters.
Check stored corms monthly. Soft spots indicate rot; firm but shriveled corms can be lightly misted to rehydrate. Discard any corm that shows extensive decay rather than risk spreading disease to healthy stock.
Image Captions & Alt Text
Image 1 — Tuberous begonia in bloom on a San Jose patio
Caption: A tuberous begonia (Begonia × tuberhybrida ‘Nonstop Salmon’) in peak summer bloom in a terracotta container on a shaded San Jose patio. Afternoon shade and consistent moisture are the keys to flowers this large.
Alt text: Salmon-pink tuberous begonia in terracotta container on shaded Bay Area patio
Image 2 — Corm storage preparation in November
Caption: Tuberous begonia corms being cured before winter storage. Allow two weeks of dry, shaded curing time before packing in vermiculite — a step that dramatically reduces rot during the storage period.
Alt text: Tuberous begonia corms laid out for curing on newspaper before winter storage
Image 3 — Rex begonia foliage close-up
Caption: The striking spiral patterning of a Rex begonia (Begonia rex-cultorum ‘Escargot’) thrives in the diffuse light and moderate humidity of a Bay Area covered patio or bright indoor window.
Alt text: Close-up of spiral-patterned Rex begonia Escargot foliage in dappled light
Author Bio
Maria Elena Vásquez is a UC Master Gardener of Santa Clara County, a horticultural writer, and a consulting botanist with 18 years of experience in Bay Area residential and public garden design. Her work has appeared in Pacific Horticulture and the San Jose Mercury News garden section. She gardens on a quarter-acre lot in the Willow Glen neighborhood, where begonias have colonized every shaded corner.
Calls to Action
🌿 CTA 1 — Newsletter Sign-Up
Headline: Get Seasonal Garden Reminders in Your Inbox
Body: Each month, we send Bay Area–specific planting reminders, pest alerts, and what-to-do-now checklists straight to your inbox — no generic advice, just what applies to your zone. [Sign up for the Bay Area Gardener Newsletter →]
🌸 CTA 2 — Local Nursery Visit
Headline: Shop Begonias at a Local Bay Area Nursery
Body: Nothing beats selecting begonias in person, where you can inspect foliage quality, root health, and bloom stage firsthand. We recommend visiting Yamagami’s Nursery in Cupertino or Summerwinds Nursery in San Jose — both carry an exceptional selection of tuberous and fancy-leaf begonias in spring. Ask a staff member about locally-trialed cultivars that perform best in our specific microclimates. [Find nurseries near you →]