Pour réussir la culture des orchidées, il faut tenter de recréer les particularités de leur milieu naturel d'origine. On doit ainsi moduler les paramètres qui influencent leur croissance et leur floraison : l’arrosage, la luminosité, la température, l’humidité relative et la fertilisation.
Tips to keep your orchids healthy
⬇ Watering | ⬇ Air humidity | ⬇ Repotting | |
⬇ Light exposure | ⬇ Fertilization | ||
⬇ Temperature | ⬇ Pruning |
To successfully grow orchids, it is essential to replicate the characteristics of their natural environment. This involves adjusting key factors that influence their growth and blooming: watering, light exposure, temperature, relative humidity, and fertilization.
Here are some tips to help keep your plants healthy:
Understanding what affects blooming
The flower parts start to develop once the plant is sufficiently mature and external conditions are right. Floral initiation is regulated by a combination of complex exterior conditions specific to the native setting of each orchid species.
Some species need a dry period, while others react to day length or seasonal variations in temperature and humidity levels.
Ensure proper watering
It is best to water in the morning with tepid, non-chlorinated water. The leaves and any roots growing outside the pot can also be lightly misted.
Watering frequency needs to be adapted to the different orchid genera, to the plant’s stage of development (plantlet or mature plant), the season (rest, growth, flowering) and the growing conditions (medium, light, temperature and relative humidity).
Tailor watering to your orchid’s specific needs
Sympodial orchids with pseudobulbs (Cattleya, Cymbidium) are adapted to daily and seasonal cycles of humidity and drought in the wild. The potting medium must be allowed to dry out completely between waterings year-round. They must be given good relative humidity, however. Water them more frequently in summer. Orchids grown on mounts may require up to twice-daily watering.
Monopodial orchids without pseudobulbs require regular watering year-round. The potting medium for Phalaenopsis and Paphiopedilums must be allowed to dry out to a depth of one-half between waterings. For Vandas, wait until the medium is completely dry, but keep the relative humidity high around the plant.
Light requirements vary with the genus and the season
As a general rule, Paphiopedilums and Phalaenopsis require moderately bright light and tolerate direct morning sun (east-facing window). In fall, to encourage blooming, they can be given brighter light by moving them near a west-facing window or closer to the fluorescent tubes if they are grown under artificial lighting.
Cattleyas, Cymbidiums and Vandas require brighter light and as much direct sunlight as possible (south- or west-facing window).
In the summer months, orchids may be placed outside, provided they are kept out of direct, intense sunlight. A gradual transition is essential, ensuring a proper acclimatization phase.
The important role of temperature
There are optimal temperature conditions for each species.
For several genera, flowering is initiated when the plant is subjected to daytime and nighttime temperature fluctuations of 5 to 10ºC until the flower spike appears. This variation must be maintained until the flower spike begins to develop.
Growing requirements for the main types of cultivated orchids
Genera | Watering | Optimal temperature oC | ||
---|---|---|---|---|
Daytime | Nighttime | Nighttime (to induce flowering) | ||
Paphiopedilum and Phalaenopsis | Allow to dry out to halfway down the pot between waterings. | 25 | 21 | 15 |
Cattleya | Allow to dry out completely between waterings. | 21 | 17 | 14 |
Cymbidium (cold) | Allow to dry out completely between waterings. | 18 | 12 | 10 |
Cymbidium (temperate) | Allow to dry out completely between waterings. | 21 | 15 | 13 |
Vanda | Water frequently. Allow to dry out completely between waterings. | 24-30 | 19 | - |
Paphiopedilums and Phalaenopsis require cool temperatures to encourage them to bloom. Nighttime temperatures must be around 15°C, normally between mid-August and late October. Once the flower stalk appears at the base of the plant, nighttime temperatures should be returned to normal, about 21°C. Learn more in this article : Getting a phalaenopsis orchid to bloom again.
Cattleyas usually require nighttime temperatures of 14°C before they will bloom.
Cymbidiums need nighttime temperatures of 10 to 13°C, depending on whether they are native to cold or temperate regions. In the south regions of Québec, Cymbidiums do best if grown outside in summer in a slightly shady spot. These plants must be brought in before the first frost, however.
Finally, Vandas, native to moist tropical Asia, need stable conditions (hot, moist and bright sunlight) year-round. To bloom, they must reach maturity; they do not require a temperature drop.
Air Humidity: achieving the optimal level for growth
Orchids generally require a relatively high humidity level. However, indoor humidity conditions are not always ideal, especially during winter. In this season, aim for a humidity level of 50% during the day and 30% at night. From spring to autumn, maintaining a relative humidity above 50% is beneficial for orchids.
To increase the relative humidity around your plants, place them on a bed of gravel in a water-filled saucer. Place the pot on the gravel, but do not allow the water to touch the pot, to avoid problems with root rot. A humidifier will also give excellent results.
Fertilizing wisely
Fertilizer is needed only during the active growing period, until flowers appear, from about February to late October.
Orchids grow slowly and appreciate dilute fertilizer at regular intervals. To avoid burning the roots, chemical fertilizers should be diluted to one-quarter to one-half the recommended strength. There is no need to dilute natural fertilizers. Accumulated mineral salts may be flushed as necessary with fresh water.
Choose the right fertilizer according to the period of the orchid's growth cycle
During the period of active vegetative growth until floral initiation begins (February to mid-August), use a nitrogen-rich fertilizer (NPK ratio: 2-1-1).
During the floral initiation period (mid-August to late October), use fertilizer that is high in phosphorus (NPK ratio: 1-2-1) alternately with balanced fertilizer (NPK ratio: 1-1-1).
Once the flower spike appears, monthly feeding with balanced fertilizer (NPK ratio: 1-1-1) is sufficient. Once the buds open, stop feeding the plant until vegetative growth resumes in spring. Watering with plain (fertilizer-free) water is sufficient until vegetative growth resumes in spring.
Where to cut the flower spike?
The flower spike on an orchid should be cut back to its base after the plant has finished flowering.
There is a single exception to this rule: a Phalaenopsis may reflower if the spike is trimmed back to beneath the faded blooms and above a latent node (see the diagram). This should be done only once, to avoid weakening the plant.
Illustration: Espace pour la vie/Audrey Desaulniers
Mastering the art of repotting orchids
There may be several reasons for repotting an orchid. These plants should be repotted if:
- the potting medium has decomposed
- the plant has outgrown its pot
- the medium does not have enough drainage
- there is a problem with root rot
Selecting the best substrate for repotting
Most orchids can be grown in containers in a variety of potting media. The materials chosen should be light and well aerated, retain moisture well and offer good root support.
The organic components should decompose slowly. The container must have drainage holes. Clay marbles or styrofoam “peanuts” may be placed in the bottom of the pot to improve drainage.
Some orchids are grown as epiphytes, attached to plaques made from cork, tree fern fibre or synthetic materials (Bulbophyllum sp.). Vandas are usually planted in slatted baskets, in coarse pieces of bark.
Finally, a number of orchid species do well when grown semi-hydroponically in inert potting material (expanded clay marbles) with natural fertilizer.
Choosing the right materials
Orchid growth substrates may be composed of a single material (tree fern fibers, coconut husk) or a combination of multiple components:
- Redwood, Douglas fir or coconut bark
- Tree fern fibre
- Cubes of rock wool
- Perlite
- Diatomite
- Charcoal
- Sphagnum moss
Sphagnum moss is not essential. It can be replaced with rock wool or diatomite (diatomaceous earth). These materials are very porous and retain water well, in addition to being well aerated. They also cut down on watering and repotting because they do not decompose.
Size of substrate components
Choose the particle size (fine, medium or coarse) according to the size of the roots and the plant’s stage of growth.
Finely crushed, water-retentive materials are suitable for plantlets and orchids with fine roots (Miltonia sp.). Medium-textured materials are used for most medium-sized plants. Coarser materials ensure better drainage for mature orchids in large pots.
Recommended proportions and sizes of potting media materials | ||||
---|---|---|---|---|
Fine (2-7 mm) | Medium (7-15 mm) | Coarse (15-25 mm) | ||
Tree or coconut bark | 1 | 1 | 1 | |
Rock wool; diatomite; fern fibre | 1 1/2 | 1 | 1/2 | |
Perlite | 1/2 | 1/2 | 1/2 | |
Charcoal | 1/4 | 1/4 | 1/4 |