How should we care for our orchids during these cold winters? Diane F.
One would think that tropical plants and snow storms are highly incompatible. Yet millions of orchid hobbyists across America are able to bridge the gap to successfully grow and bloom a wide range of orchid genera by creating healthy horticultural microclimates within their homes. The months of December, January, and February offer the greatest challenges, as well as the greatest rewards - if executed correctly.
The winter solstice occurs on Dec 21st – a time when the sun is at its lowest point on the horizon and the days are the shortest. In Virginia, daylight begins around 7am and ends around 5pm – a mere 10 hours of natural light. (Things could be worse. Iceland, for example, has only one hour of daylight.) In general, tropical plants are their happiest during long warm months, since these botanicals are found naturally near the equator where they receive balmy conditions year round. So what is an orchid hobbyist from Virginia to do?
South-facing windows become increasingly important as winter approaches. However, sunlight streams in almost horizontally with a blistering intensity that seems unlikely given the icy temperatures outside. Many orchids have been scalded in this seemingly innocent southern exposure – a painful reminder that even in the dead of winter, orchids generally can’t take full sun. The solution is to somehow filter the sun to a dappled effect so that the plant leaves are never warm to the touch. Common techniques include drawing sheer curtains, partially closing blinds, and placing other objects in front of leaves. The popular genera that require this treatment are Cattleyas, Dendrobiums, and Oncidiums.
The other two favorite types – Paphiopedilums (aka Lady Slippers) and Phalaenopsis will burn to a crisp in south-facing windows since they are shade loving plants. Northern as well as heavily filtered east and west exposure is most suitable.
Shorter days slow foliar growth to a near standstill. It’s hard for photosynthesis to occur in the dark! Don’t expect much in the way of new leaves or pseudo-bulbs at this time. In some respects, the plant is resting…hibernating…taking vacation. So it stands to reason that fertilization should be minimized or eliminated during the winter. The extra nutrients won’t hurt anything - they just get washed down the drain unused.
Flower spikes for the sun loving genera such as Dendrobiums and Oncidiums will drop off dramatically and buds counts will be wanting on those plants that attempt to bloom. Cattleyas will behave as they always do – producing flowers seasonally based on their breeding lineage. Those with the species C trianaei and C perciviliana will bloom like clockwork around Christmas – all others will be waiting for their designated month.
The mottled-leaf Lady Slippers are free spirits and send up buds on a whim – any old time. Their flower stems are extra tall and majestic during the winter as they ‘stretch for the light’. It’s not uncommon to have a two foot stem supporting a large proud bloom. The complex or ‘bulldog’ paphs only bloom at this time so it’s now or never. Watch the new growths for emerging buds which could produce flowers the size of soft balls.
December is also the calm before the storm for Phals (aka Moth Orchids) as nearly every last plant should be spiking. The growths may be just a few inches tall or they may already have pea sized buds on them. Start staking the stems when the buds resemble marbles. It can be a long wait before the first flower first opens – typically three months but the reward is great - three more months of perfectly shaped moth-like blossoms. Their blooming season is always January through May unless they’ve been forced.
A few final notes for winterization: Air circulation should be maintained as this helps to reduce the potential for rot. Supplemental humidity may be required as home furnaces dry out the air. Consider humidity trays or even small humidifiers for larger collections. Re-pot only those plants which are desperate since leaf and root growth won’t occur until spring. Thorough watering is still required at least weekly and, by all means, resist the temptation to use ice cubes. No tropical plant likes cold water on its roots. And good news! Insects should be few as they are in conference, planning their springtime attack.