|Disa Culture Guide||Pictoral Tour|
Disa are tuberous terrestrial orchids from South Africa. Culture for the species fall primarily into two categories. Category 1, which comprise most of the species, have a dormant period following flowering. They flower from spring into early summer followed by their dormant period which lasts until mid fall. The dormancy is a response to dry hot conditions in their habitat. Plants in this category should not be watered while dormant. Category 2, comprise most of the hybrids and a handful of the species currently on the market. The following culture information pertains to this group of Disas.
In nature these species D. uniflora, tripetaloides, racemosa, cardinalis, aurata. are found growing in the moss along mountain streams. Their roots are continuously bathed by cool clean mountain spring water all year long, while their leaves are exposed to bright light. Daytime temperatures during the summer can easily reach 90 degrees in the sun while the water around the plants roots is a cool 50 degrees. Night time temperatures can drop to 50 degrees. During the winter it's not unusual for temperatures to be near freezing.
Cultivation: The plants growth cycle
During the cool winter months the plants grow slowly. Disa grow rapidly once spring air temperatures increase and days begin to lengthen. Plants mature enough to flower will send up inflorescences starting in February through March and April. Flowering begins around the end of March and lasts through June. Shortly after flowering the main plant will die back, while simultaneously producing a new tuber. This tuber will then become the flowering plant in the following spring. New plants may also be produced around the base of the old plant and by underground stolons. Plants produced in this manner usually are tuberless and take several seasons to reach flowering size. This is the time of year to repot your Disa! Taking extra care not to damage the fragile roots and the new tuber. It is not unusual for an immature tuberless Disa to stop growing and produce a tuber, thereby entering the normal growth cycle. It is also not unusual for a large tuberless Disa to flower. When this happens the plant will usually spend all its energy in flower production and not have enough reserve left to produce a tuber for next season. Do not let Disa plants without tubers flower!
Disa are tolerant to a wide temperature range. They can take near freezing to over 100 degrees in full sun. The most important factor is to keep the ROOTS COOL and Wet, particularly when summer temperatures climb. You can accomplish this by flushing the pots with cool water several times a day, providing good air circulation to facilitate evaporative cooling from the surface of the pot, shading 30-50% to cut down on solar heating, using light colored pots.
Disa NEED high quality water. Water high in dissolved solids, and contaminates such as chlorine must be avoided. Reverse Osmosis, Deionized, Distilled, Rain, water are all suitable. Other sources such as well and tap water should be tested. Do not assume that water low in dissolved solids is safe to use. If sodium ions comprise the main portion of the dissolved solids, the water will be toxic regardless of the total level of dissolved solids (TDS). Disa should never dry out. They should be fertilized frequently with a balanced plant food. Total dissolved solids after the fertilizer addition should be in the range of 250ppm. A rough estimate would be 1/16 - 1/8 teaspoon per gallon of water. When using very pure water such as RO, Distilled, Deionized, and Rain, care must be taken to use a fertilizer with added minor elements such as calcium, sulfur, magnesium, iron etc. A fertilizer designed for hydroponic culture would be ideal. pH also must be considered with these water sources since they contain little buffering salt such as calcium, addition of fertilizer often makes the final solution very acidic. The pH should be between 5 - 6.8
The potting media must hold a lot of moisture and provide excellent aeration. I have used pure New Zealand sphagnum, silica sand with a little peat moss, peat moss blends with perlite/vermiculite, rockwool, and fine bark mixed with perlite and sphagnum. Personally I think the NZ sphagnum gives the best overall results. It can hold a large amount of water and packed loosely in the pot allows excellent aeration. Repot Disa when any of these circumstances exist. The seedling has grown too big for the pot. The pot has become filled with plantlets from underground stolons. The plant has died back in the early summer and is making new growth from the new tuber. The surface of the growing media is covered with algae. The plant looks sickly. The only rule I follow on when NOT to repot is in the late winter/early spring when a mature healthy plant is producing an inflorescence.
Pests and Diseases
Rot and more rot. Disa are not troubled by
many different pests and diseases. Unfortunately
they are prone to rot caused by fungus, probably
either a pythium or phytophthora. This rot
strikes fast, often turning Disa plants into
brown mush in a matter of days. The difficulty
is due to the soft tuberous and succulent
growth of the plant combined with the disease
starting in the root zone and working it's
way up through the central stem of the rosette.
Good culture and frequent careful observation
is often enough to keep the disease in check,
even more so during warm humid weather which
naturally stress the plants. Fungicides such
as Subdue 2e, Benomyl, and other systemics
designed for pythium and phytophthora applied
periodically as a preventative spray/drench
will help greatly. Care must be used with
these chemicals as they often will cause
chlorosis in developing leaves. Even with
the best culture and careful observations
expect to lose Disa to rot!
Soft scale, spider mite, aphids, and fungus gnats will occasionally be a problem. Mild insecticides such as Safer soap work well against pests which attack the leaves and flowers. Fungus gnat larvae can do a considerable amount of damage to the roots and underground portion of the plant. They can be controlled by frequent repotting and if necessary a Bt drench. Always test untried chemicals on a few plants initially!!
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