Guidelines for growing some of the Special Begonias:
Well, sure! While many might think of Begonias as care-free windowsill plants, or even as outdoor annuals! Begonias, like Orchids, are a vast and varied family; they contain many species and types, not all of which require the same care.
Most of those I grow and offer are plants that need a bit more attention to humidity and moisture. Oftentimes, terrarium or greenhouse care is required. Some example species included here are: B. chlorosticta, B. decora, B. luzonensis, B. microsperma, B. versicolor, B. prismatocarpa, and so many others.
These and so many other similar species & hybrids are best accommodated in humid greenhouses OR in terrariums. Growing under artificial lights is also a common arrangement that allows for easier temperature management (artificial light typically will heat up terrariums like natural sunlight will).
In addition, some Begonias can also be of a tuberous type. Those of this nature, such as Begonia taliensis, Begonia henryi, & B. pearcei, do best is a seasonal dry and coolish rest is provided - typically during the winter. For these, please review my method of resting.
Some general recommendations:
Lighting: Most Begonias of these types are not overly fond of high light. Typically, I aim for a bright, diffuse, low-to-medium level (1000-1800 foot-candles on average). Not enough light will result in elongated stems and leaves, weak, easily damaged and disease prone tissues, poor blooming, and also a general lack of vigor. Too much light, on the other hand, can often result in yellow-bleached or reddish-tinted foliage, sometimes even a stunted or contorted look - especially since the higher light is often coupled with lower humidity.
Moisture / Humidity: Most of the species really prefer fairly high humidity, up around 70-90%. Too little and these plants will dry out too quickly or even desiccate (simply dry up)! Too much and they can be subject to disease attacks and/or root rots. Strive for a lightly damp media that never becomes "bone dry" nor remains excessively wet for extended periods. Do allow them to briefly approach being dry between watering (but do not allow the humidity (air moisture) to fall too low. Water quality, as is for so many specialized plants, should be a consideration. Many plants of this nature do not appreciate a high mineral content, chlorine, or excessive salts in their water. I use collected rain water, and/or reverse osmosis for most of the year. To this, i add fertilizer with trace elements, and adjust the PH, if/as needed to around 6.0.
Note: some species seem to resent moisture on the foliage. This can come in the form of drippings, or even condensation. While they respond very well to terrarium culture, it is best NOT to wet their foliage when watering. Should condensation start to form on the foliage, or leaves that touch the edge of container covers, be sure to aerate to reduce moisture.
Temperatures: Most of these plants respond best to intermediate to warm temperatures (range of 60 - 85F). Cooler temps will slow them considerably and also cause leaf drop or dormancy if exposed for long periods of time.
Interestingly, however, some - such as B. limprichtii, B "U512" , and "U498" have been found to be surprisingly tolerant of cool winter nights in a greenhouse setting. Several of these have done well with nights in the low 50's - with attention to not overwater during that time.
Feeding: During the spring-summer months - or as long as the plants appear to be actively growing, i try to ensure they receive adequate and sufficient supply of nutrients. this is best provided via a good quality, complete (with micro nutrients & trace elements), fertilizer. Brand is not as important as following the mix ratio suggested by the manufacturer. Do keep in mind that the warmer the weather and brighter the light they are receiving, may dictate the frequency of the feeding needed.
Substrate / Media: This varies depending upon the container and watering practices - but, in general, strive for a loose, somewhat airy medium. I've had great luck with a mixture of: Pro-mix (HP w/biofungicide), Perlite, and/or sometimes a little chopped Sphagnum. In general, a ratio of the above that works for me is roughly - 2:1:2. The ratio of all these ingredients can vary depending sometimes upon the plant itself as well as whether it is to be grown in a closed terrarium or in an open greenhouse. For those known to grow natively in Limestone regions, I also add a small percentage (usually just 2-5% by volume) of Limestone CHIPS to the mix. Whatever media is used, remember that a healthy well-developed root system is paramount to good growth of the plant. If you're not seeing good root activity, then something is off and needs adjustment.
Terrarium Containers: Many of these plants (especially the smaller ones) are shown to the best advantage when "grown under cover" in containers to themselves. For these, berry bowls, aquariums of all sizes, or any decorative glass container may be used. I typically include a shallow layer of gravel or chunky charcoal in the bottom to assist in having a place for excess water to drain (most of these containers do not have holes in their bottoms). On top of the drainage layer will go the compost of choice (see above paragraph), the depth of which will depend on preference, available height within the container, and the plant being grown. Usually, 2-4" depth is sufficient. Once planting is complete, a light watering is given - enough to ensure the medium is dampened, but not so much that the result is soggy. The container may now be covered - how tightly depends on a number of factors. If the foliage of the newly planted terrarium is wet, I usually leave the top off until the excess has evaporated. Once the foliage is "dry", I often cap them pretty tightly - a plate glass lid, or other cover can often be used - it will seal quite well, but not be 100% air tight. In the absence of a nice lid, a simple layer of saran wrap can also be used. This, if sealed tightly, probably should be lifted every few weeks to check for moisture and allow for some fresh air. In general, using terrarium-like containers for culture greatly simplifies and eases the attention required to grow many of these treasures.