Begonia tenuissima

The genus Begonia comprises over 2000 described species, found in tropical and subtropical regions worldwide, where they inhabit every conceivable habitat from desert to rainforest. Some of them are very rewarding, easy, and fast-growing houseplants, while others are highly specialized inhabitants of primeval forests and can only be cultivated in terrariums. It is therefore almost impossible to give general care tips for begonias that truly apply to all species.

However, as a rough classification, one can orient oneself by growth habit, size, and leaf color:

• Species with purely green leaves usually originate from open, sunny habitats and are better suited as houseplants.
• Species with very colorful, curiously shaped leaves are usually more suited as terrarium plants. An exception to this are the very colorful so-called "Rex Begonias".
• Large, upright growing species (cane begonias) are usually also more robust than small, flat growing species (rhizomatous begonias).

Depending on which group they belong to, they should be cared for accordingly. More on this in the other tabs.

This begonia originates from the undergrowth of rainforests, and as such, it is adapted to semi-shaded to shaded conditions. It grows best in a sheltered environment with high humidity, such as a plant cabinet, terrarium, bottle garden, or grow tent.

When cared for under grow lights, moderate lighting is sufficient. It thrives and the leaves develop ideal coloration at 2000 to 5000 lux, or 35 to 100 PPFD (µmol/m²/s).

It prefers a humidity of 70% or more and still grows well at over 90% RH. The leaves should not remain constantly wet and ideally should not be misted. Plant pathogenic fungal spores can germinate more easily and penetrate the plant on wet leaves.

It should always be kept above 20°C, including in the pot or substrate. Temperatures above 30°C should be avoided.

This begonia likes a fine, but airy and consistently moist substrate.

In nature, this plant grows in very nutrient-poor soil. In the rainforest, there is little to no humus, as one knows it from native forests. A thin layer of leaves/detritus, only 1 to 3 cm thick, is usually followed directly by dense clay soil or rock. The roots of the plants creep along the surface under the thin leaf layer and almost never penetrate deeper than a few centimeters into the soil.
Therefore, this plant should be potted in a loose, only slightly acidic (pH ~ 6 to 6.5) and very airy mix. We recommend our houseplant mix or a mixture of sphagnum and perlite in a ratio of 3:1 for this plant. It also grows well in a purely mineral substrate like our ASP mix.

The pot for this plant does not have to be particularly large. A pot that is too large will cause the substrate to be dry at the top but still wet at the bottom. Then one quickly thinks one has to water and drowns the plant, which is actually still moist enough. Even when planted in a terrarium, no deep substrate layer is needed. The roots usually do not penetrate deeper than about 5 cm into the substrate.

Begonias can be kept in surprisingly small pots and can also remain in fully root-bound pots for a long time. Well-established, healthy plants tolerate repotting well and can also have their roots trimmed by about 30% when repotted or divided.

This begonia prefers soft water and should therefore be watered with distilled water, rainwater, or water from an osmosis system. It should never dry out completely.

This is a rather slow-growing species that does not require too much fertilizer. Regular complete fertilizer (N-P-K + trace elements) for houseplants is sufficient. We recommend reducing the manufacturer's recommended dosage by about a third (which corresponds to about 300 µS/cm conductivity of fertilizer), but fertilizing weekly. The conductivity can be determined with a TDS meter. For stronger leaves and stems, a potassium-rich fertilizer (e.g., cactus fertilizer) can be used instead of a standard fertilizer.