AMES, Iowa — Tuberous begonias are available in upright and trailing types, single and double flowers and a wide variety of vibrant colors and flower forms and are a gardener’s favorite for easily brightening a shady corner of the garden. Unfortunately, they will not survive harsh winter weather outdoors and must be dug in the fall and stored indoors through the winter months.
Now is the time to begin thinking about getting them out of storage and ready for spring planting. Here are some tips from Iowa State University Extension and Outreach horticulturists on dates and procedures for starting tuberous begonias.
Tuberous begonias are prized for their large, showy blooms and ability to thrive in shady spots By starting begonia tubers indoors early in the season, you can enjoy bigger, fuller plants and earlier flowers once moved outside. Follow this complete guide to learn proper techniques for starting tuberous begonias indoors
Why Start Begonia Tubers Indoors?
Getting a head start on begonia growth indoors offers several advantages
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Earlier blooms – Begonias started indoors bloom weeks sooner than planting the tubers directly outdoors. Enjoy color faster!
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Bigger plants – With more time to develop roots and foliage, indoor-started begonias are often larger and fuller.
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No frost risk – Begonias are very frost sensitive. Starting tubers inside eliminates any chance of cold damage.
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More variety – A wider selection of begonia varieties is typically available as tubers versus young plants at garden centers.
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Cost savings – Purchasing tubers is usually more affordable than buying pre-grown begonia plants.
For impatient gardeners in short-summer climates there are lots of good reasons to get a jump on begonias indoors!
When to Start Begonia Tubers Indoors
Most gardeners start begonia tubers 6-8 weeks before the estimated last spring frost date for their area. This gives adequate time for roots and leaves to develop before moving the started plants outside.
Refer to this general timeline:
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Begin starting tubers in January/February for zone 7 and warmer.
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Start tubers in February/March for zones 5-6.
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March/April starts work for cooler zones 3-4.
Aim for begonias to have 3-5 leaves by the time they are transplanted outdoors. Monitor your area’s long-range weather forecasts to determine the optimal starting window.
Selecting High Quality Begonia Tubers
When purchasing begonia tubers for starting indoors, look for:
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Firm, not shriveled – Avoid tubers with mushy spots or excessive wrinkling.
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Unbroken skin – Damage or cuts provide entry points for rot.
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Visible buds/eyes – Look for a distinct depression with small buds protruding from the hollow side.
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Medium size – Bulbs 2-3 inches across have good nutrient reserves to fuel growth.
High quality, healthy tubers will have the best chance of vigorous sprouting when started indoors.
How to Plant and Grow Begonia Tubers Indoors
Follow these steps for success with starting begonias inside:
Use Small Pots
Plant one tuber per 4-5 inch pot so roots have room to expand. Terra cotta pots allow excess moisture to evaporate.
Provide Drainage Material
Add crockery shards, pebbles, or peat moss in the bottom of pots to promote drainage. Tubers rot if soil stays too wet.
Use Loose Potting Mix
A light, fluffy starting mix gives tuber roots the aeration they need. Blends containing peat or coconut coir work well.
Plant Tubers Correctly
Lay bulbs horizontally with the indented hollow side facing up, 2 inches deep. Gently cover with potting soil.
Water Sparingly At First
Until sprouts appear, water just enough to keep soil barely moist. Too much moisture will cause tubers to rot.
Increase Water As Growth Starts
Once shoots emerge, begin watering more frequently to encourage begonia growth. Fertilize lightly.
Give Warmth and Light
Optimal soil temperature is 70°F. Provide bright indirect light or use grow lights to spur development.
With proper planting and care, most begonia tubers will sprout in 4-6 weeks when started indoors.
Hardening Off Begonia Seedlings
Begonias started indoors must transition slowly to outdoor conditions to avoid damage:
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Set plants outdoors in filtered shade for a few hours at first.
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Gradually increase time outside over 7-10 days.
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Monitor weather forecasts and avoid cold nights or frost.
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Allow plants to return indoors at night until fully acclimated.
Hardening off toughens plants by slowing adapting them to sun, wind, and outdoor temps. Take it slow for the best results.
When and How to Transplant Started Begonias Outdoors
Move begonias outside only after danger of frost has passed.
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Plant in morning or evening to avoid midday heat stress.
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Water transplants well and provide shade for 1-2 days.
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Pinch off any weak, damaged leaves and stems.
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Use rich organic potting mix with excellent drainage.
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Give plenty of space between plants for good air circulation.
With proper hardening off and an attentiveness to weather conditions, transplanted begonias will transition smoothly and continue growing vigorously.
Ongoing Care of Started Begonias
Once your begonias are settled into the garden, keep them looking their best:
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Water thoroughly when the top inch of soil becomes dry. Avoid wet feet.
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Fertilize every 2-3 weeks with a balanced diluted liquid feed.
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Pinch off spent blooms to encourage more flowering.
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Monitor for pests like aphids or mites and treat any found immediately.
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Prune back leggy growth to keep plants full and compact.
With the right care after transplanting, your begonias started indoors will reward you with vivid, abundant blooms all season long!
Tips for Growing Gorgeous Begonias from Tubers
Follow these guidelines to maximize success with starting begonia tubers indoors:
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Select plump tubers free of blemishes or damage. Discard any skinny or shriveled bulbs.
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Use containers with drainage holes and a lightweight, fluffy starting mix.
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Plant tubers horizontally with indented hollow side up, just below soil surface.
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Provide bottom heat of 70°F and grow lights 14+ hours per day.
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Once sprouted, give more light and water but avoid overwatering.
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Hardening off before transplanting outdoors prevents shock and leaf scorch.
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Move started plants to garden only after danger of frost is past.
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Pinch off weak growth and deadhead spent blooms to encourage more flowering.
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Fertilize every 2-3 weeks and monitor for pests. Enjoy the color show!
With the right techniques, growing begonias from tubers started indoors is very rewarding. The extra time and care you put in will pay off abundantly once those big, bold blooms start showing their beautiful faces in your summer garden!
When should I plant tuberous begonia tubers indoors?
Plant tuberous begonia tubers indoors eight to 10 weeks before the average last spring frost in your area. (Flowering typically begins 12 to 14 weeks after planting.) Start tuberous begonias in pots or other suitable containers. All containers should have drainage holes in the bottom. Use a well-drained potting mix. When planting the tubers, place the concave or indented side upward. The rounded side is the bottom. Cover the tubers with one-half to 1 inch of potting soil. Water well. Then place the containers in a warm, 70 degree Fahrenheit location. Since the tubers are susceptible to rotting, keep the potting soil moist, but not wet. Once the tubers sprout, move the plants to a sunny window or place under fluorescent lights. Fertilize plants with a dilute fertilizer solution every two to four weeks.
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AMES, Iowa — Tuberous begonias are available in upright and trailing types, single and double flowers and a wide variety of vibrant colors and flower forms and are a gardener’s favorite for easily brightening a shady corner of the garden. Unfortunately, they will not survive harsh winter weather outdoors and must be dug in the fall and stored indoors through the winter months.
Now is the time to begin thinking about getting them out of storage and ready for spring planting. Here are some tips from Iowa State University Extension and Outreach horticulturists on dates and procedures for starting tuberous begonias.
How to Start Tuberous Begonias Indoors
FAQ
How to start off begonia tubers indoors?
- Sterilize pots if reusing from last season
- Pre-sprout tubers in a warm place of your home by setting out until sprouts form
- Fill 4 inch pots 2/3rds full with potting soil
- Place 1 begonia tuber into pot pressing into soil gently.
- Cover with 1 inch of soil
- Set in warm place of your home or on a heat mat
Can tuberous begonias be grown indoors?
Tuberous begonias can also be grown indoors but do best as temporary flowering plants rather than long-term indoor accents because their growth cycle includes a dormancy period when flowers and foliage both die back. Fibrous begonias are prized for their charming year-round flowers.
When should I start my Begonia tubers?
Pre-start your begonia tubers inside, 8 weeks before the last frost. As previously mentioned, begonia tubers won’t survive in cold weather so you will want to start them indoors. Follow these easy steps to give your begonia tubers the best start in life: You can buy your tubers in garden centres between January and April.
How do you grow tuberous begonias?
If you are growing tuberous begonias in the ground, allow these plants to grow as long as possible up to the first frost. At this point, dig up the tubers with a small amount of soil around them and allow to dry in a sheltered location like a garage or shed.
How do I start begonias indoors?
Starting begonias indoors requires a few supplies and a little extra work, but the rewards are worth it months later. The first step to planning for starting begonia tubers is to buy begonia tubers. When shopping online for begonia tubers at Holland Bulb Farms a wide selection of begonias are available.
How long does it take to grow a tuberous begonia?
Dormant or store-bought tuberous begonias can be started indoors in late winter or early spring (about 8 weeks before the last frost) by placing them in a warm area with indirect light to reacclimate and sprout. This should take a few weeks.
Do tuberous begonias need to be dug up?
In most areas, tuberous begonias will need to be dug up and saved over the winter, so keep that in mind when placing your plants so you can easily access the tubers when it is time to overwinter. Tuberous begonias also work well in containers on shady patios and porches with filtered sunlight.
How do begonias grow?
These begonias are grown for their showy flowers and typically have a rounded growth habit. They grow from underground tubers, which store nutrients and energy for the plant. Tuberous begonias often have large, double blooms in a wide range of colors, including red, pink, orange, yellow, and white.