Starting begonias from seed indoors - A complete how to guide

Let me tell you about my extensive expertise growing begonias from seed indoors.

Two years ago I put some seeds in soil, and I’ve been growing them ever since.

Did you expect more? Pfft.

I’m not a master gardener or a horticulturist (yet), and I haven’t been growing begonias for years. So what’s my street cred growing em?

I don’t have any. You don’t have to be an expert to grow most begonias. You don’t have to be an expert to grow almost anything. Get some soil, find some light and plant some flowers. You’ll thank me for it in the summer.

Flats of pink and white fibrous begonia seedlings

Most begonias are easy to raise from seed, easy to care for, and easy to love. They fill baskets, window boxes, and flower beds with non-fussy blooms all summer long. They also make shaded areas pop with color and vibrancy. I’m a bit obsessed with them. I’m a bit obsessed with all flowers but begonias are my special favorite. I dry hundreds of them in the summer to use for craft projects in the fall & winter.

That’s why today I am planting 400. No lie, I am going to start 400 tuberous and wax begonias in my house today. That might sound excessive, but I plan on filling two extensive flower beds in the front of my house. 400 will guarantee I have enough.

So How do I grow begonias from seed without a greenhouse?

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I set up a room in my house as a temporary indoor grow room every year.

You need space. Any space really, so long as it’s in a heated room. If you’re going to start small and plant a few flats, my simple set up will be perfect for you. It doesn’t take up a lot of space and is easy to put up and take down. Since the racks stack into one another, they don’t take up a lot of storage space when not in use.

Is it cost-effective to grow your Begonias from seed?

Tuberous begonias are not cheap if you buy them at the garden center in spring. I’ve seen the nonstop tuberous begonias for $4.99 CDN each. I want to plant 400! There is no way I would spend that kind of money on flowers. But I will pay $30.00 CDN for a few packs of seeds.

I’m often surprised that more people who garden don’t start seeds indoors. It’s true that it’s a cost up front to buy the grow lights and shelves, but even that can be DIY’ed for significant savings.

I grow about 100 flats of flowers in the winter and spring indoors. That might sound like a lot but I keep adding growing racks each year, and I keep finding things I want to grow.

This is the year of the begonia for me (oh and the year of the dahlia, oh and the year of the geranium). You see my problem.

This what my house starts to look like during planting season.

Begonia Seeds and where to find them.

I buy my begonia seeds from Stokes Seeds Canada. They have an incredible selection, best prices, and fast shipping. When I can’t find the flower seeds I want from Stokes, I often buy from William Dam & Veseys. I’ve had excellent results from those vendors, so I have no problem recommending them.

Both Stokes and Veseys sell seeds in the US, but there are countless fantastic seed vendors in the US.

What type of begonias?

I am growing the same begonias from seed as I did last year. The tuberous begonias are Non-Stop, and the fibrous begonias are Bada Bing.

The nonstop flower is beautiful with big double blooms. They do look like old-fashioned flowers, and I dig that. They feel like flowers that belong in a cottage style garden. You can also pull them up in the fall and replant them the following year.

The Bada Bing Wax Begonias have smaller delicate flowers but bloom profusely. I used them in my window boxes last year and had people stop and ask me what they were quite often. They are annuals, so unlike the Tuberous Begonias, you will not be able to save them. Think of them like any other annual. You can find Wax begonias reasonably priced in the spring. I choose to grow mine from seed because I am guaranteed the kind and colour I want.

There are 1000’s of begonia seeds out there. I list two that I plant here because they were easy to grow. Any begonia seeds that you find from a commercial seed vendor will work. So find something you like best and give it a try.

Be sure to buy pelleted seeds. Begonia seeds are fine, so fine that they look like dust. Pelleted seeds have the advantage of being larger and much easier to plant.

Recommendations:
Fibrous Begonias- Bada Bing/ Bada Boom.
Tuberous Begonias – Non-Stop

Seed starting materials

Soil

I start my seeds in Pro-mix seed start & vermiculite. I’ve used a few different seed start mediums, but I like Pro-mix the best. This year I bought a bag of Miracle Gro seed starting soil, and it was full of twigs, chunks of wood, you name it. Pro-Mix is much finer and easier to use. It also produced excellent results for me in the past.

I add pre-moistened Pro-mix seed start to 72 cell trays before adding the seeds. I add a small pinch of vermiculite over the top of the seeds. Begonias do need light to germinate so don’t add too much vermiculite.

Recommendations: Pro-Mix Seed Start/ Pro-Mix Container Mix

Trays, cells & domes

I use 72 cell trays for my begonias. They are inexpensive and reusable. To avoid contaminating this year’s crop be sure to clean and disinfect any trays or cells that you reuse.

If you don’t know what 72 cell trays are, they are seed starting trays that are divided up into 72 cells. You can find cell trays in lots of different sizes, but 72 is pretty standard. It’s what most of your annuals come in every year.

You don’t have to start with 72 trays; you can use anything to start your seeds. Just pinch out your seedlings and pot on from any size. I happen to like the 72 cells best.

Recommendation: 72 Cell 6/Pk Tear Away Inserts

6-inch Pots

You will also need containers to transplant into on when your seedlings outgrow their tiny cells. I use 6-inch pots, but you can use 4-inch peat pots, or any container larger than 4 inches. That’s 4 inches deep and wide. The Begonias need the space to spread their roots.

Save your plastic containers, like yogurt or sour cream and reuse them over and over. Make sure you cut holes into bottoms for drainage.

Recommendation

6-inch nursery pots
4-inch peat pots
reusable kitchen containers

Watering Trays & Domes

You will also need a waterproof tray to insert your seed cells. Having a tray under your cells allows for bottom watering. It also keeps the water off your floor!

Domes. You also need a top to cover your begonia seeds while they are germinating. I use these domes (over and over again). You can use plastic wrap. You need to contain the humidity and allow light. Anything that meets that criteria will work for a covering, but plastic wrap is cheap and works fine.

I recently bought a 72 cell, tray, and dome in a kit for $4.99. I couldn’t find a link, but if you want trays and domes in a full kit just look around your local hardware store, they are very popular and easy to find as the gardening season starts to roll around.

Fertilizer

While the begonias are in the 72 cells, you will fertilize once a week at half strength.

After potting up to the 6-inch pot continue to fertilize once a week but use regular strength. Begonias are heavy feeders. If you don’t fertilize, they will not perform.

I use pro-mix flower fertilizer. I used it for the first time last year and had excellent results.

Recommendation:
Pro-Mix Fertilizer for Flowers. But any flower fertilizer will do.

Lights

You will need a light source. Although Begonias are shade plants, they do need light to grow as seedlings. Lack of light will cause the tuberous begonias to put energy into the development of the tuber. The begonia plant will stop producing leaves and plant will no longer be viable.

I don’t use fancy lights. I did have a rack of fancy spectrum lights for growing plants indoors. They didn’t do as well as the regular old cool fluorescents. Your mileage may vary here, but I can tell you from my experience last year that any regular old fluorescent lights will work.

Begonias need 15 hours of light at the start. Some folks use a timer, and that is a GREAT idea. For me, I like to visit and turn the lights on and off so I can see if they need water.

Recommendation: Brightech LightPRO LED Shop Light

Heat Source

Begonias germinate at 75 f degrees. They will have difficulty germinating over 85f and under 65f. I use a heat mat under the seed trays. I picked mine up on sale for $19.99 (CDN) a few years back.

You don’t have to use a heat mat. You could try germinating your seeds over a vent or heat source like a fridge or any warm area in your home. The germination rates may be spotty, but it will still work.

Recommendation: Milliard Durable 15″ x 11″ Waterproof Hydroponic Seedling Heat Mat / Warm Heating Pad / or any gardening heat mat that you can find at your local garden center.

Potting Up your begonia seedlings

I transplant my seedlings to 6-inch pots once they start to outgrow their small cells. Usually after the fifth leaf.

At the end of April, I remove the begonias from the indoor grow room and place them on window sills. I also put them on tables, desk, benches. I have to put them everywhere. They take over. You will have flowers everywhere. It’s a good problem to have.

hardening off of your begonia plants

Our last frost date is May 24th. I usually prepare for that date by hardening off all my plants starting May 1st.

Hardening off means exposing your spoiled little seedlings to their new harsh environment. Winds, bright sunlight, rain, fluctuating temperatures. Your tiny seedlings have been in a perfect climate. If you plant them now without hardening off, you’re going to lose many of them.

I usually start hardening off early in the morning. Since Begonias are shade plants, I harden off on my covered back deck. This protects the plants from any harsh sun.

I start off with an hour and add about a half hour every day. Toward the end of the month, if the weather is co-operative, I will start to leave them overnight on the back deck.

They should be ready to plant after three weeks.

You may find they are a bit worse for wear after their first few outings. I thought I killed my seedlings the first day I put them out because they came back inside in poor shape. They quickly bounced back, and they eventually adapted to life outside.

Planting your begonia seedling outside in the spring

Both the fibrous begonias and tuberous begonias like well-drained soil. They thrive in hanging baskets and containers. They also work great in flower beds so long as the soil is adequate. I can recommend the fibrous Bada Bing for planters, they are well mounded and have a neat, orderly appearance.

These are shade plants, and they are perfect for the darker areas of your yard. I planted my begonias last year on my front step and window boxes. That side of the house gets almost no sunlight, and they thrived.

Begonias do not like to have wet feet. Too much water will cause them distress. Too much water from overhead could cause powdery mildew as well. Take care watering like you would your vegetable garden. Water when they need it, don’t over water, and try not to water from overhead.

I installed a few drip hoses last summer around my flower beds, and they worked very well. I plan on installing them throughout my begonia beds this summer. They are quite inexpensive and make watering your garden a snap.

Outdoor Soil, spacing, and fertilizer

I add granular fertilizer and work into the soil well before planting. No surprise here that I add time released Pro-mix. I follow-up with a weekly feeding of liquid fertilizer throughout the summer.

Each plant has different spacing requirements. I usually go 8 inches for the fibrous and 12 inches for the Tuberous. I plant tight in containers. In a 14 inch basket, I would plant four fibrous or 3 tuberous begonias. I like my baskets and window boxes full and overflowing.

garden care

Once your little begonias get planted in the ground, they pretty much take care of themselves.

Beyond fertilizer every other week and watering, they don’t have any particular requirements. You can deadhead, but I have found that it doesn’t make a difference, they just keep blooming for me even if I forget or neglect them.

Saving tuber for next year

If you are in zone 7 or 8, you can overwinter your begonias in the ground, and I hate you. Well, I don’t really hate you, I’m just jealous.

Honestly, if you read this far, I love you.

If you’re not in zone 7 or 8 and like me live in the tundra (zone 3A Canada), you can overwinter too. It’s a bit of a process, but it’s worth it.

Saving your begonias for next year will only work with your tuberous begonias. Unfortunately, your wax begonias are annuals and will not overwinter in the same way.

After the first light frost in the fall cut back your tuberous begonia and gently pull them from the ground. I do this with a garden fork and a light hand.

Clean the tubers with clean water and let them sit in the sun for a few days to dry out. You can store them in sawdust, peat moss, paper bags or anything that will keep them dry. I store mine in labeled paper bags with a bit of peat moss. They then get placed in a clean cardboard box, and they then get whisked away to the basement until next spring.

Your overwintered begonias need a cold spot in your house that doesn’t freeze but doesn’t get too warm.

What to do with your begonia tubers in Spring.

About eight weeks before my last frost I’ll bring out my cardboard box and inspect the bags. If I have any rotting or bad begonia tubers, they get tossed out into the garbage. Don’t put them in your compost.

Spring bulbs get started early in our home so we can get a jump on the season. My trick is to start the tubers in paper bags. I give two paper bags a light coating of cooking spray. I know this sounds odd, but it keeps the bag together until it is time to plant out. Once the bags have a light coating of cooking spray, I put one inside the other and roll the tops down until they are about 4 inches deep.

I then add 3 inches of potting soil and place my begonia tuber on top. To this, I add 1 inch of potting soil. I give it a good water and put it in a warm sunny window.

I let them grow like this until the 3rd week of May when I finally plant out. I put them in the ground still in the paper bags. It works like a charm.