Answer: Bedding begonia seed is almost dust like so purchasing pelleted seed makes sowing much easier. Seeds take about 2 weeks to germinate when kept at 70F.
It is very important that the containers you start the seeds in be very clean. If you are re-using plastic seed flats from last year or if you are using saved food containers (yogurt cups, salad bar boxes, etc...) it is wise to use a mild bleach solution to disinfect them. All containers must have holes in the bottom to allow drainage - seeds want to be moist not soaking wet. For this reason you may want to use a rimmed tray to set your containers in.
Fill your containers with dry potting soil. Soil-less mixes are best and can be purchased just about anywhere. If you want to make your own mix simply combine four parts peat moss, four parts vermiculite, and one part perlite. All of these items are available at your local hardware or garden store. Next, and this is important, thoroughly soak the soil in the containers with warm water and gently tamp down the wet soil. This creates the warm, moist environment that seeds need for germination.
Place several seeds in each container. Bury the seeds at a depth that is roughly two times the size of the seed itself. For the smallest seeds just cover them with a light sprinkling of dry potting soil. Place the seeds in a spot with moderate light - not in direct sunlight. Normal household light will be sufficient in most cases.
Cover your containers with plastic wrap or use the domes supplied with seed flats to keep the soil from drying out too quickly. Check your containers once or twice a day and mist them with warm water as necessary. You do not need to use fertilizers during germination as all of the necessary nutrients are already in the seed itself.
When your seedlings emerge and the first leaves are opening it is time to remove the heat and give them more light. They need about 16 hours of bright light each day. That means a sunny window is less than ideal. Most gardeners find that placing the plants under 40 watt fluorescent bulbs works best. Bulbs should be placed several inches above the seedlings and raised as the plants grow. Some people use a timer for their lights but we find it just as easy to turn them on when we wake up in the morning and turn them off when we go to bed.
Now that the seeds have become seedlings they will need some feeding. We still recommend misting as a way to water the plants and at this point we add a balanced plant fertilizer diluted to half strength to our spray bottle.
If you put several seeds in each container you may now notice that some of them are not as strong as their container-mates. The weakest and spindliest seedlings need to be cut so the strongest ones will be stronger. If more than one strong plant is in a single container you may opt to carefully remove and transplant them to their own containers. There is no sense in attempting heroics to rescue weak seedlings as their chance of surviving the move to the garden is slim at best. That's precisely why you should place more than one seed in each container to begin with.
As the seedlings get bigger they will need to be moved to bigger pots in order to keep their growth momentum going. We usually use peat pots that can be set directly in the ground after last frost.
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