By Ron Maunder (from Orchids in NZ 19.5, 1993)

The species Odontoglossum crispum is found in Colombia, South America on the western slopes and spurs of the Cordillera Oriental in the Andes. The habitat is cool and moist at an elevation of 2250 to 3000m and they are mostly found growing on trees (epiphytic), although some can be found growing on cliff faces. They receive bright light but do not like direct sunlight or the leaves will burn. Plants receiving too much light will often show reddening of the leaves.

Flowers are displayed on arching stems and are generally beautifully lined in two rows all facing in one direction with about six to 12 blooms. Odm crispum flowers are white with a few brown spots in the centre. Many plants exhibit some pink flushing in the petals but the pure white are the most sought after. The edges of the petals are beautifully ‘crisped’ as though someone spent hours cutting frilly edges on them.

The first specimens were collected by Theodore Hartweg in 1841 but were not described by Lindley until 1852. Surprisingly, it was not introduced into cultivation until 1863. Charlesworth in England did a lot of hybridising with the various species and Odm crispum many years ago and most of the good modern hybrids can be traced back to that nursery.

Under the ideal temperature range, Odontoglossums will grow all year round and in Tauranga they seem to flower on a 9-month cycle. My houses have mesh benches to allow maximum air movement and the floors are granulated pumice which is damped down three or four times a day in summer. Fans keep the air continually moving in my Odontoglossum house. The houses have Novalite roofs and open sides with a plastic material that can be rolled down on frosty nights to prevent cold air coming in.

I use 3-1-1 (NPK) fertiliser with practically every watering during summer but this is a weak solution. The plants are kept in small pots for the size of the plant with 15cm pots the maximum I use. My potting mix comprises quarter bark chips (no dust) and 20% by volume of shredded Oasis (florist’s foam). [A more ‘normal’ type of mix is outlined in the fact sheet link at the end of this piece – Ed]

Odontoglossums should be repotted every 2 years, sooner if you’re concerned about the quality of the mix. Don’t pot on, but completely shake out the old mix and repot in new material. Repot only if there is a 2- or 3-month growing period ahead. Because of the heavy watering and fertiliser programme, the potting mix gets mossy quickly and the top inch or so is scraped off and renewed every 3 months. A few slow-release fertiliser pellets can be scattered on top at each change of top mix but only 6-10 pellets on a large pot. Plenty of drainage holes should be added to the bottom of the pot.

Watering should be done early in the day so leaves are dry by night.

At repotting time back bulbs can be removed but don’t cut them to fewer than groups of two as the plants seem to initiate shoots better from two or more back bulbs. Flowers of sulphur is used as a fungicide on all cut surfaces.

Die-back of leaf tips indicates trouble in the potting mix. Maybe it’s too old and needs changing, but too much fertiliser can cause this problem too.

Odontoglossums and their related genera often suffer from concertina or pleated leaves, a sure sign that the plant isn’t getting enough water. From my observations, young growths can have difficulty forcing apart and watering can also help this problem.

Editor’s note: This useful fact sheet notes that a number of intergeneric hybrids have been made using Odontoglossums. These include crossing with Brassia (Odontobrassia), Miltonia (Odontonia), Cochlioda (Odontioda) and Oncidium (Odontocidium). Often these hybrids produce flowers closely resembling the shapes and colors seen in Odontoglossums, yet the plants will thrive under much warmer conditions than purebred Odontoglossums.

For the purists, it’s worth noting that Kew has renamed Odm crispum as Odm alexandrae. However, the American Orchid Society still uses Odm crispum.