> Volume 67 (November/December 2000, pages 223 - 226)
Growing Begonias Indoors
by Brad Thompson
Except for the members that are blessed with a climate
where they can grow begonias outdoors year round, most growers have to
learn how to grow begonias indoors. Sometimes it's only for the winter
months, but for some plants and people it's a year around proposition.
Most houses, especially those with forced air heat,
are not perfectly suited for growing begonias indoors. Most begonias can
be grown in your home, however, if you are careful to provide each with
its particular requirements. There are also a few tricks that will help
make growing them in the house more successful.
1. Location and Light
The first consideration is where exactly are the
begonias going to live. The best light for growing indoors is to use
fluorescent lighting. This will give you the most control over the amount
of light your plants get. It doesn't have to be an expensive or lavish
setup. Even a simple shop light with ordinary cool white tubes will
suffice if you want to save money. A more expensive, but possibly more
useful idea if you plan to start a larger collection of plants is to
purchase a light stand. These can be bought from most mail order catalogs.
The lights should run about 14 hours a day, but I have left lights on 24
hours a day and the plants did fine. The tubes should be just a couple
inches above the tallest plant on the shelf.
Most of us also have natural light that we would like
to take advantage of. There are begonias that will grow in nearly every
window location except probably not well in a north window. Some plants in
terrariums may grow fine in a north window, however. Different areas of
the country vary as far as light intensity during the months of the year.
You might have to experiment to find which plants grow in which windows.
If you find that the plants are stretching, they need more light and if
they are stunted and burning then they need to be farther from the window
or moved to a window with less light. A good share of begonias will grow
in a south window and most will grow in either an eastern or western
2. Pots and Potting Mixes
How your plants are potted and what soil mix you use
will have a lot to do with how successful you are. Begonias hate to be
over-potted or over-watered. It is hard to kill an under-potted begonia,
but they can die pretty fast if over-potted. Don't move begonias to a
larger pot until roots have filled the current pot. If you find that a
certain plant never seems to dry out, it is probably in too large of a
pot. Move it down to a size that fits the rootball after you've removed
all the soggy wet mix.
For growing indoors you should always use a soilless
mix. Nearly all soilless mixes are mostly composed of peatmoss with
additions of perlite and/or vermiculite. You can also make your own by
mixing two thirds peatmoss or a peat based mix with a third part perlite.
A couple of commonly available peat based mixes are Sunshine and Fafard.
If you use plain peatmoss you should premoisten it before using because it
can sometimes be hard to wet in the first place. When I use peat, I wet it
with boiling water to get it slightly damp and then use it after it cools.
I wouldn't recommend using any amendments you would commonly use outdoors
such as leaf mold or manure, or even garden soil. These will cause your
mix to stay too wet indoors and also invite diseases. A peat mix is the
perfect mix for indoors since it drains well, but holds the perfect amount
of moisture for the plant without staying too wet. I would use the same
mix for begonias in terrariums.
As far as watering goes, a good pot for using indoors
is the type called a self-watering pot. There are many brands and they
work well for most begonias. You should also only use a peat based mix for
these types of pots; anything else will stay too wet.. Allow the mix to
dry out slightly before refilling the reservoir again.
Regardless of what you have read in indoor gardening
books, there are few plants that want to stay constantly moist. Besides,
constantly moist is near impossible to achieve. Allow the surface of the
mix to dry out slightly and then water thoroughly till water runs out the
bottom when using conventional pots. Don't use saucers unless you fill
them with pebbles so that the plant doesn't sit in water. You can use
bottom watering, but empty the water out of the saucer after a couple of
hours. Most begonias will also grow well using wick watering such as is
used for African violets and gesneriads.
Humidity is the biggest problem with growing begonias
indoors. Although begonias don't like to be in wet soil, they do like
humidity in the air. You can achieve enough humidity for many types of
begonias by simply misting them daily. You can also use a humidifier. If
you are growing plants under fluorescent lights a simple way to keep good
humidity is to cover the plant stand with a plastic tent (make sure to use
nonflammable plastic). They will still usually benefit from misting inside
the tent because if the light fixtures are inside the tent they tend to
keep it warmer and the air will dry out faster.
There are many begonias that are easier to maintain
and that you will have greater success with if they are grown in
terrariums. It's possible that your past attempts with terrariums have
soured you on them, but if you follow a few simple rules you should do
well with them. Most people keep their terrariums too wet and this is the
most common reason for failure. You should only use a sterile medium for
growing and this should only be damp.
The two most common mediums are the peat mix listed
above or plain green sphagnum moss (don't use the brown florist type
sphagnum). If you use peatmoss, first put in a layer of perlite or pebbles
in the bottom covered by a thin layer of mix. This will allow any extra
water a place to drain. If you use sphagnum, wet it first with hot water
and squeeze out the extra water before using. Peat and sphagnum are
already basically sterile and if you take the added precaution to wet with
boiling water before use, it will be even more so. There will always be
some glass fogging after planting, but if it's excessive, crack the lid
open until it has dried out enough that you can close tightly. Terrariums
require less light than plants in pots and should never get direct sun.
They should also not be fertilized often. Since the soil in a terrarium
never gets flushed, the salts will build up and damage the plant.
All plants that
are actively growing do best with regular fertilizing. There are many
brands of fertilizer formulated so you can fertilize every time you water
by adding a few drops to the watering can. You can also just mix your own
weak fertilizer such as quarter strength and use once a week.
7. Additional Notes
Begonias grown indoors can be pinched or pruned any
time of the year. Any plants you bring indoors from outside will probably
adjust easier if you trim them back. This will also give you cuttings to
start a back up plant in case your plant doesn't do well with the change
Indoor plants in nice warm conditions are very prone
to mealy bugs. The easiest and least toxic mealy bug killer is plain
rubbing alcohol. You can brush the mealy bugs with a cue tip or artist
brush dipped in the alcohol and they die on contact. For a badly infested
plant you can also put the alcohol in a spray bottle and spray the entire
plant. It won't harm the plant. Avoid spraying the soil directly as a
Hope this article gives you a few ideas and helps you
to grow begonias indoors