Home > Begonian > Volume 58 (July/August 1991, pages 130 - 132)

High Humidity Begonias
by Bill Voss

One day in the late 1970's I received in the mail a group of begonias I had ordered. Among them was B. brevirimosa. I was new to growing begonias, other than the wax begonias of childhood.

I was at a loss as I watched the three plants of B. brevirimosa, in pots, disintegrate before my eyes. I made a panicked call, and Millie Thompson advised me to get them into humidity of 70% or higher. As most of the leaves were gone already, she also advised me to make some leaf cuttings as a backup. I soon have over 30 new plants and a better understanding of the needs of brevirimosa and other begonias that require high humidity.

Many of the distinctive looking begonias require a higher level of humidity than our air conditioned and heated homes provide. This is especially true for begonia species such as bogneri, chlorosticta, serratipetala, Symbegonia U012, versicolor, U089, et al. Placing them on a tray of moist pebbles is not a workable solution as it is for many other begonias; their humidity requirements are greater. Perhaps this is why so many of them are difficult for us to find.

If you are up to the challenge of raising these beautiful and unusual begonias, you must keep them in enclosed atmospheres. The container can be anything: a large terrarium, bubble bowl, plastic sweater box, or a clear plastic 3 liter soda bottle. Sales at discount stores or yard sales can keep prices low if you are looking for a terrarium or bubble bowl.

Growing in terrariums is different from growing in a pot or in your garden. Because water does not drain out, adjusting the amount of water is a challenge and overwatering is easy to do.

In some of my containers (especially in soda bottles and sweater boxes) I deal with this problem by growing the plants in pots to allow for better drainage. However, if the plant is to be grown for show, you should be aware that pots are not usually allowed in contained atmosphere classes.

In most bubble bowls and terrariums I place a layer of perlite in the bottom for drainage, add some soilless mix, and plant in the mix. Charcoal is also recommended, to keep the mix from going sour.

Some of the begonias like their roots to stay on the dry side while other do well in a moist soil. To satisfy them all I basically use two different mixes. The drier mix is a 50-50 mix of fertil mix (a local brand name) and perlite (this is also my standard cutting mix for most of my begonias. The more moist mix is ProMix bx (usually sold in large amounts to commercial growers; your nursery or garden center might order it for you) with more perlite added.

Some begonias, such as brevirimosa, will grow taller than 3 feet high. There are some tall aquariums that are excellent for them. I grow exotica, brevirimosa, and serratipetala in a large plexi-glass aquarium 28" high, with a heating cable in the soil as they like the warmth. I also use the moist mix. I never let their roots get dry (this can happen with a heating cable). They appear to thrive with roots on the moist side. Leaves that fall will root quickly.

For Begonias bogneri and chlorosticta I keep the soil on the drier side. I also reduce the light level and use no heating cables. B. versicolor also does well in a cooler environment.

B. bogerni has been know to collapse suddenly, without warning; this happened to me when I had it in a heated terrarium. The leaves fell limply from the plant. I quickly removed it and placed it in a cooler sweater box. It came back in about a month. This revival was probably possible because the plant was several years old and its base was large. A young single plant that hasn't clumped would probably have just melted down and been lost.

Symbegonia U012 is another plant that thrives in a cool and moist atmosphere with reduced light. It does well for me in a curtained east window or off to the side of fluorescent lights. I don't grow it directly under the lights. I keep its roots moist. This duplicates its native habitat in New Guinea, where it grows above the 5000 ft. level, near streams or other water sources, and is always shaded.

Imitating the plants' natural environment is one of the keys to finding success in growing these begonias. Read the begonia books, find out where the plants grow in nature, and try to imitate their environment as much as possible. If the habitat is unknown, try different growing methods; observe the plants closely - they'll let you know quickly if they're happy or not.

As backups for failures, take cuttings. Share your cuttings with other growers or botanical gardens as this is another good backup to prevent losses from being total ones.

Locating some of the more exotic begonias can be a challenge. The ABS Seed Fund is a great way of getting seeds for these types of begonias inexpensively. As you get to be a proficient grower, maybe you can help get others started by supplying seed for the Fund.

Once you have mastered growing in a contained atmosphere you'll find that plants require less attention on a daily basis than those in pots or your garden. Because the amount of watering and daily care needed are reduced, the high humidity begonias often can be put in decorative glass containers and placed in an office or other areas where humidity is not ideal for begonias.

Try growing some of the difficult begonias, and help keep them from being lost to us. It's a job you will find enjoyable.

To the left is B. bogneri, drawing by Mary Weinberg.

Below is one of the author's high humidity habitats.