Tuberous Begonias

Mother Nature is having a hard time letting go of winter here this year.  It is cold and blustery this morning with a temperature of 19 degrees and with wind, it feels like it's only 2 degrees outside.  I need to do some tree pruning yet before the trees break dormancy for the season, but that will wait for a nicer day.  I love being outside, but I don't like being cold!

Wiese Acres tuberous begonias

So, today, I'm going to dig my tuberous begonias out of their winter storage place and give them a head start for the spring and summer.  There are several types of begonias, but the only ones I save from year to year are the tuberous begonias.  Tuberous begonias put on a glorious display all summer long.  There are varieties in red, yellow, pink, peach, salmon - just about every color you might like in your garden, except blue.  There are varieties with single flowers and varieties with double flowers.  The tubers can be kept for many years, making them a good investment. 


They are not winter hardy, though, so in any zone that experiences frost, they need to be lifted and stored in a frost free place for the winter.  Tuberous begonias must have a period of dormancy so they are not suitable to keep inside over the winter as houseplants. 

In the fall, after frost has spoiled the foliage but before it is cold enough to chill the soil much, I bring the pots of begonias in to the garage.  Begonias can be planted directly in the garden, but I prefer leaving them in pots.  It makes the job of bringing them in for the winter much easier.  I remove all the foliage and cut the stems back to just a few inches.  I leave the tubers in the pots until the soil has dried some.  That makes it easier to lift the tubers from the soil.  Then I remove the tubers from the soil, spread them on newspaper until the remaing stem and the roots have dried.  Then I remove the dried stem and roots and pack the tubers in layers in an apple box filled with peat moss.  That apple box then goes into the cold room, where it stays about 40 degrees and is dry, until about mid-March.  I check periodically over the winter to make sure there are no rotting or molding tubers and remove those as I find them.

Today, I'll take the tubers out, inspect them for any signs of rot or mold again, and plant the healthy tubers in their summer homes in well-drained, light potting soil.  I fill the pots with that well-drained potting soil to about 2 1/2 inches from the top.  I moisten the potting soil then place the tubers on top of it.  The tubers have a slight, dish-like depression on one side - that is the side that should face up in the planter.  Some of the tubers are over-achievers and have already begun to grow in their winter home.  These must be handled carefully to avoid breaking the new growth, which is very tender.  I'll carefully cover the tubers with about 1/2 inch of moistened potting soil and place the pot in a spot where the temperature stays about 65 to 70 degrees.  If the tubers have already begun to show signs of growth, I usually see leaves begin to emerge within 1 to 2 weeks.  Those who aren't quite such over-achievers will begin to peek their new leaves through the soil within about 3 to 4 weeks.  I can hasten their growth some by placing the pots on a seed starting mat or placing them closer to a heat register.  The tubers are very susceptible to rot during this time, so it is important to keep the soil evenly moist but never soggy.

Once new growth is visible, place the pot in a location that get bright light but never direct sun.  About two weeks before I expect the last frost, I'll start "hardening them off" by moving the pots outside into a protected, shady location, during the day and bringing them back in when temperatures start cooling off in the afternoon.  Eventually, they will be moved to their permanent summer home under the box elder tree in the front yard.

Begonias will tolerate early morning or late afternoon sun, but must have light or dappled shade the rest of the day.  They are a perfect plant for a shady location where it is otherwise difficult to have brightly colored flowers growing.  In pots, they will need water nearly every day, but it is important to test the soil before watering.  I'll use a high-tech test to determine if my begonia needs water.  I'll stick my index finger into the top inch of the potting soil and if it is dry, I'll water.  If it is still pretty moist, I won't.  If the soil is kept too wet, the tubers may rot.   If the soil gets too dry, the flowers will drop and the leaves will develop dry, brown edges, turn yellow and fall.  Once a month, I'll feed them with a balanced 20-20-20 fertilizer.

The tubers that I start now should be blooming in all their glory by early July.  Earlier blooms that will last all summer can be achieved by earlier planting - tubers started in mid-February will be blooming by mid-June, or about 3 1/2 to 4 months after planting.  I wait to start mine because of the challenges of keeping the plants from getting too leggy if they are grown indoors for too long a time.  Even though I sacrifice a little of my bloom time by waiting, overall I have a much nicer plant for the entire summer.  Then, in the fall, after the first frost, I'll bring them back in and start the cycle all over again.