Diana's understanding is pretty accurate. To the extent of my research, no
one really knows what causes the summer-blooming Phals and Doritis to
initiate spikes. If someone does know, please clue me in!

But for the vast majority of Phals and Dtps. that generally bloom in winter
or early spring, the biggest and most reliable trigger to induce new
inflorescences is a diurnal (day/night) temp change of somewhere around
12-15F. Adding magnesium to the fertilizer can also help, but I don't think
it will be enough without the temp change. Decreasing hours of daylight
(which happens naturally in fall) also helps, but the temp change is the
"biggie."

One way to "nudge" them is to water at sunset. This cools the roots more
quickly and "fools" them into thinking the temp change is present, if you're
on the borderline. But it carries a big risk of inviting fungal and
bacterial infections.

Now, once you've got this spike started, if it grows up in hot temps,
chances are it's going to be long and leggy, and not produce many flowers --
very disappointing. That's where that 75F max comes into play.

Phals with previously-bloomed spikes that are still green can make more
flowers, sometimes from the end, more often from a secondary branching lower
on the stem, and these seem less dependent on temps, but these bloomings,
too, are very disappointing compared to what the plant is capable of on a
good primary blooming.
--
Kenni Judd
Juno Beach Orchids



"Diana Kulaga" wrote in message
...
Hi, Xi,

I will answer this only with respect to winter blooming Phalaenopsis. It's
my understanding that Phals in our collections aren't really being
'forced', but rather exposed to conditions that mimic what they would
encounter in nature at a given time of year. I grow outside here in FL,
and the weather naturally cooperates in late October, November and
December by giving the plants the drop in temperature that they require to
spike, without any help from me.

For those growing in greenhouses (and I am no expert on that, having never
experienced greenhouse growing), I expect that they need to manipulate the
diurnal temperature range for these plants.

Now, what I consider 'forcing' would be done by a commercial grower in
order to have blooming plants for shows, etc, during a season when they
would not generally be in flower. I don't see anything wrong with that,
but the plants will likely return to their normal blooming season
afterward, possibly taking a season off to get some rest.

Just my understanding.

Diana