Chris Dalrymple

In the colder months, the requirements of orchids changeLower temperatureLess light intensityShorter daysLess evapourationSlower growth

Ref www.worldweatheronline.com

Average Sunshine Hours per DaySydney vs Melbourne (which is why we don’t live there)ref www.livingin-australia.com

How you approach winter will depend onWhat orchids you growWhether you have heatThe potting medium and potThe air flowOverhead coverageFrostWind protectionThese factors are interconnected

What orchids you growDo they need a temperature drop to initiate

flowering?Do they require/tolerate drying of the root zone

between watering or need some degree of constant moisture?

What are their conditions in their natural habitats?What are their light requirements?Are they potted or mounted?Some warm growing orchids may be grown cold if

kept dry in winter months

Potting mediumBark will hold moisture for some days; coconut

husk for longerThe larger the particle size, the larger the air

spaces and the faster the dryingPerlite/inert media generally dry fasterPolystyrene dries rapidlyAll the above depends on air flow ie. the more

airflow the faster drying of any mix of mediaKnow what your potting medium does

The potsThe wider the pot, the slower it will dryThe deeper the pot, the slower it will dryMost orchid pots now have excellent drainageBasket ‘net’ pots and square ‘vanda’ pots have

even better drainage and will dry faster

How do you judge how rapidly the mix is drying?

Have different sized pots of your mix with no orchids in them, watered at your usual frequency with everything else

You can tip them out without disturbing a plant to see what is happening in the pots, winter or summer

Not absolutely accurate as no orchid organic matter in the pot but is indicative

AirflowAlways desirable for growing orchidsThe faster the flow, the faster the dryingWhat are your prevailing winds in summer vs

winter?Wind temperature is important in winter –

orchids do not like cold wet rootsDo you require improved airflow in winter?Fans in closed houses +/- heat when vents are

shut

Bulb rot secondary to waterlogged roots

Overhead coverSolid cover allows control of exposure to rainWinter rain, particularly Sydney rain, is coldRarely protection from hailWill decrease light intensity depending on

material usedIt can be removed for summer

FrostClose to the coast, rarely a problemInland may be a major problemCan be devastating to a collectionBe aware of your frost patterns, usually at

lower elevationsOccurs when there is no air movementProtect by physical coverage or improved

airflow

Wind protectionWhile some airflow is desirable, strong winds

may cause damage to a collection either potted or mounted

Colder winds will cause more damage when pots remain wet

Increased risk of fungal infections in these conditions

Note that winds may dry mounted and hanging plants very quickly

Light intensityWill depend on the aspect of the orchid house

and ambient conditions eg tree coverageAs a general principle, the more light in winter

the betterAdjustable factors such as removing denser

shade cloth used in summerAdjuvant lighting may be considered in some

situations

Adjust watering habitsWill depend on whether orchids are potted or

mountedMorning watering onlyDecreased frequency depending on ambient

conditions ie. no watering when cold and raining, wait for a clear day

Clear days will have colder nights so the earlier the better

Adjust watering habitsHave a strategy to cope with a mixed collectionMisting vs watering for humidityBe aware of hanging plants dripping onto pots

belowWhere possible avoid leaving the foliage wet

which may result in leaf damage, lessened by good airflow and early watering

Leaf water damage

Adjust your collectionGroup similar plants together

potted vs mountedthose requiring some constant moisture vs

those tolerating a dry interval vs those deliberately kept dry over winter

similar potting mixesdo not be afraid to omit waterings

This will simplify watering the collection

FertiliserFertilising should be decreased or ceased

completely in the colder monthsThe plants do not require much food when not

growingCosts money for no advantage to the plant

Watch your plantsPots remaining heavy between wateringsSigns of drying with shrivelling of pseudobulbsSigns of fungal infection with root/bulb rotSigns of secondary infection by scale or mealy

bugBe ready to alter your watering regimen or

adjust conditions if you detect any problemsIf a plant shows a problem, change somethingor you will need

DEATH CERTIFICATETHE ORCHID

GENUS: SPECIES:PRESENTED TO

CONDITION POORPROGNOSIS DISMALMANAGMENT INTENSIVEOUTCOME KARKED IT

THIS IS AN EX-ORCHID, DROPPED OFF THE PERCH,

FELL OFF THE TWIG, GONE TO ORCHID HEAVEN

 RIP

Good growing