Although there are over 130 species of Disa available, by far the most commonly grown is Disa uniflora (which is native to Table Mountain near Cape Town) and cultivars stemming from this species. Disa uniflora has the largest flowers in the group in the richest reds to be found in any orchid. There and lots of crosses with blooms from pale yellow through deep crimson. The Disas in the uniflora group and their hybrids are typically evergreen and are tuber based plants which produce flowers borne on 15 - 20 inch tall stems carrying between 3 and 7 flowers up to 3 inches across. They are excellent as cut flowers and will last well if kept in water. Flowering normally begins in late spring and can continue until early summner.
Fortunately for us they are also one of the fastest multipliers of all orchids. Having spoken to, and seen his collection, Howard Taylor of Yorkshire (one of the UK's leading experts in Disa orchids) tells me that from pollination to seed production can be as short as 5 weeks and that seed, unlike 'normal' orchids which has very specific germination requirements (see orchids from seed) can be sown directly on to sphagnum moss compost mix with exceptional results. Flowering size plants can be had in just 2 years - almost a biennial!
Lighting & Air for Disa Orchids
Disa orchids like plenty of light but not strong, harsh light, you should provide 30% - 60% shading during the summer and allow more light in the darker months.
Disa like good air flow and so can be kept out of doors during the summer and early autumn, suitably shaded of course. Alternatively place an oscillating fan in the greenhouse to keep the air constantly moving and thus preventing stale pockets of air, oscillating fans are better then a strait forward one as they don't cause permanent draughts on one plant.
Watering Disa Orchids
Feeding Disa Orchids
Feed Disa orchids with general purpose fertilizer at quarter strength from March till September at which time you should begin feeding with a higher potash feed at quarter strength to help harden the leaves and stems ready for the cooler winter. In both cases apply the feed at every second to third watering making sure to flush the pots at least once a month with fresh clean water to remove any excess salts. Cease feeding in late October and resume the following March.
Re Potting Disa Orchids
Disas should be re potted every year or whenever the pot is full and after flowering (flowering typically Feb - May n the UK), re potting on a regular basis is advantageous and will encourage the plant to grow better and stronger. Tip the plant out of its pot and remove the existing compost, replant the tuber (or thick roots) in a pot large enough for 12 months growth. Aim to get the plant and stems at the same level in the new compost as it was in the old compost before giving it a thorough flooding of plain water, and then flood again after 20 minutes. Normal watering can resume after a week.
I'm told the best way to remember to repot your Disa is to think of the time the clocks change in the UK, re pot your Disa orchids just before the clocks change in either the spring or autumn depending on whether they are of a suitable size or in spike.
Propagating Disa Orchids
Disas are easily propagated by potting up any loose tubers or side shoots that have developed during the previous season. Newly potted tubers will be flowering size in 1 - 2 to years depending on the size of the tuber/side shoot which should be removed and potted in the standard mix AFTER flowering, in the UK this means June/July.
Remember, These orchid MUST remain damp at all times!