Documents: Special Interest: Orchids:

Orchids - Wondering Why
by Marilyn H.S. Light
July 27, 2008

Dendrobium

Ruth asks about her first orchid, a Dendrobium, and by her description of the flowers, a pretty one too! Dendrobiums such as the one Ruth now owns are hybrids derived from Australian orchid species. They require bright light, intermediate temperatures (with a 5 C change between night and day temps), regular watering when actively growing, and weak weekly fertilizer applications also when the growth is active. Dendrobiums often flower once their annual growth is complete so the time to feed and water is beforehand, when new leaves and roots are forming.

The more energy an orchid can store during growth, the more and better coloured flowers it will produce. Sunlight and mineral nutrients are important to growth. Try raising this orchid in a window behind sheer curtains, in a sunroom, an intermediate greenhouse, or about six inches beneath two wide spectrum fluorescent tubes. BC is known for its overcast skies in winter so some supplementary light may be in order. The plant will be reasonably resistant to dryness but intolerant of 'wet feet' especially if kept too cool or if watered when the roots are inactive.

Check what the plant is potted in (it should be in medium bark chips). If the chips still seem to be in good condition (not degraded into a mush), you can poke your finger into the pot to feel if the inner chips are still damp. After awhile, you will know that the plant needs watering just by its weight but in the meantime, do the 'finger test'. Use water with low amounts of dissolved mineral salts. Rainwater, melted snow, deionized water are all fine.

Fertilize your orchid according to its growth cycle and the growing conditions that you can provide. The rate of growth will depend upon temperature, the amount of available light, and water. Try to balance the fertilizer application rate with the amount of growth that the plant can manage. When in doubt, apply more dilute fertilizer first and observe the response. Your goal is to have a bigger, more substantial shoot than the one before. The leaves should become sturdy, never floppy. I recommend liquid fertilizer products such as 7-7-7 containing micronutrients. Start with 1/4 the recommended dilution and watch the root tips. Arrested root growth can be the first sign of fertilizer burn or mineral salts accumulation. Fertilize weekly, watering heavily with plain water once every month to wash away accumulated salts. Best of luck with your first orchid!

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