May Orchid Care Calendar

Compiled by Dixie McCulloch, a longtime KOS member who joined in 1988.

Temperature Range (˚F)DaysNights
Cool house61-6555-61
Intermediate house70-8160-70
Warm houseup to 9070-75

With the higher outside temperatures the temperature inside will increase greatly. This means you will need good air movement in the greenhouse to keep the temperature down around the plants. The temperature can be reduced by increasing the humidity in the greenhouse. It can be done in several ways. Some ways to reduce heat are: watering the inside of the greenhouse down; adding misting nozzles that come on when temperature gets too high; or you can install an evaporative cooler. Also shading will reflect the heat to some extent. Remember to keep up your fertilizing program.

Towards the end of the month, as warmer nights prevail, the more hardy plants, like Cymbidium, Dendrobium, Coelogyne, Bifrenaria, Odontoglossum, Masdevallia, Stanhopea, Gongora, Pleione, Laelia, strap-leaf and terete-leaf Vanda, plus others, may be placed outside. A patio or sheltered place in the yard may be used, but some protection from the sun must be provided. You can also put plants in a small-unheated greenhouse or lath house, depending on the weather. Emergency heating should be available in the event of sudden temperature change, or you may have to move them inside. Plants should only be gradually exposed to the abundant light. This can be controlled by the use of shade cloth, a lath house, or overhanging tree branches, to avoid overheating of the leaves that could result in burning. Remember, with lower outside humidity they will have to be watered more often.

Cattleya and Laelia: On sunny days spray with water several times a day. Plants that are fully established should be given as much fresh air as possible. A suitable humid atmosphere can be created by spraying the floor and benches. Species Laelia pseudobulbs are to be kept firmer than Cattleyas. This is done by giving them more light and air, and less heat. They may even be placed outside. Water more frequently; plants need more water to efficiently utilize increased food and light levels that are typically available now.

Paphiopedilum: All species must have plenty of shade throughout the summer and fall. Remember, these are terrestrial orchids. In their native habitat they grow on the ground, beneath tall trees and seldom see direct sunlight. Make sure they are well watered during the growing period. This is probably the ideal month to complete repotting of your “lady’s slippers.” Remove dead roots and keep as many growths together as practical. Monitor light levels to be sure that these plants receive adequate shade and cool temperatures. Keep root-zone moisture levels reasonably high; occasionally mist the foliage. The Brachypetalum types generally prefer drier conditions.

More and more growers are learning not to splash water between their plants. This is the primary infection source for many water-borne diseases and bacterial problems on cultivated plants.

Phalaenopsis: Good growth occurs only with high temperature and humidity. You may repot your Phals if they have finished flowering. Wait for the emergence of a new leaf in the crown before proceeding. When you repot, remove the old inflorescence and eliminate all rotten or completely dehydrated roots.