Let’s face it, this is a very important part of the process, but it also depends a lot on what you’re using for soil, and containers. A newly opened bag of germination potting soil is nearly sterile, and new plastic containers are unlikely to be contaminated, so this is the simplest way to get started. However, if you are reusing containers, sterilizing becomes essential. In general do not recycle soil for starting Begonia seed, there is simply too much risk of contamination. Always start with a clean, tightly sealed potting mix.
The easiest way to sterilize is to use boiling water. Rinse all your pots and containers or soak them in the very hot water. Be careful you don’t use a plastic that will melt in the heat. If you want to avoid the risks of hot water, then making up a 10-20% solution of bleach and water (⅓ – ½ cup bleach in 1 gallon water) also works well for containers. Definitely wear gloves, as bleach is very hard on your skin. Use a plastic bucket and let pots soak for a few minutes, especially if there is any lingering dirt from previous use.
Some also soak the filled pots, or potting mix, in near boiling water for a few minutes, it is a personal choice. If you have a fresh, new potting mix it is likely not necessary.
Preparing the Pots
Fill your pots with the prepared potting mix and settle it down by gently tapping the container on a hard surface. Allow a quarter of an inch or so for watering. Some recommend soaking the pots of soil and only adding the seed to the saturated potting mix. Watering once the seed has been scattered can be tricky, as it is very easy to wash the seed away.
Planting the Seed
First make a label with the name of the plant you are sowing and the date. Put the label in the pot before you plant it. Since begonia seed is so fine, it’s hard to keep track of which ones are planted, if you don’t put the labels in first. Pre-labeling will save you lots of trouble in the long run.
Again, the seed is like dust, so some growers will mix 1 part seed to 3 parts sterile sand (not beach sand as that has too much salt in it), shake the package of seed a few times to mix seed and sand equally. Plant the seed by scattering the package over the surface of the soil.
Make sure you do your planting away from the other pots you’re planting. The seed is so small, you could end up with some of it in nearby pots if you aren’t careful. For a roughly 2” container about 50 to 100 seeds is all you need. If you don’t have good vision, you’ll just have to wing it. Begonia seeds seem to prefer company and germinate and grow best with many in the pot, but if you plant too many seeds, you’ll have trouble separating them. It is a bit of a balancing act, but you’ll get the hang of it.
Don’t cover the seed, as begonia seed needs light to germinate. Use a spray bottle of the ¼ strength fertilizer to water the newly planted seed in. A spray bottle is easy to use and the mist is so fine it doesn’t blow, or wash, the seed away.
After you have sown seeds in your pots, place them into a sealable container so that they are in very high humidity. If you do not cover the pots, the surface of the soil and seeds dry out too fast and repeatedly, so if they grow at all there will be very few seedlings. They can come up in as quickly as 4 days or not for a month.
See how other members do it!