is it good idea to fertilize the orchid with every

[asif]

i live in karachi at times the temp goes nearly 40 c so is it a good practice to give a dilute fertilizer with every watering any suggestions please

[Ray]

At that kind of temperature, you're probably seeing pretty active growth, so I'd say "yes".

If, on the other hand, the evaporation rate is quite high (due to low humidity), you might be better off to alternate that with plain water in order to keep the medium well flushed.

[asif]

it was a great way to manage humidity but i want to send some orchids to a friend at a place but where he lives the temparature goes up to 50 C in summer and humidity is low so shall i advise him to water the orchid twice but in winter the temp drops to 4C in the night i think to cover the whole green house with plastic file and leave the water on the ground instead to water the plants please adivse

[Blueszz]

Not all species and hybrids can take temps as low as 4C, even when you keep the rootsystem dry. Your friend might need additional heating during the winter, depending on the kind of orchids he is going to keep.
Spraying the ground during hot periods and low humidity can be a good way to raise the humidity in the greenhouse, but I don't think it will do much for him during the cold weather. At least not when it comes to preventing the orchids to die from the cold. Otherwise, keeping the ground wet might raise the humidity level also during the colder months which the orchids probably like. Spraying them when it's cold could cause rot and fungal problems - orchids shouldn't stay wet for too long. Running a fan might be a good idea too.
As for the watering regime (x times a week) I can't say useful things. It depends on many more factors than temperature alone: humidity, growth, temperature, size of the plant, kind of medium the plants is potted in, mounted or not etc.

Nicole

[asif]

nice and help tips but we cover the greenhouse with as we cover put net that will be benefical or not

[Blueszz]

Covering the greenhouse with some material that insulates will be benefitial but if that will do? You might cover the inside instead of the outside, that way it won't get damaged by the wind etc.
What kind of orchids do you want to send him?

[asif]

why dont you recommend me some like we get den onc phap phal but den do really good as beginners orchid in pakistan i think i will send den

[Blueszz]

With these low temperatures stay away from Paphiopedilum and Phalaenopsis. Australien den's might do very well, also Den. nobile. Recently I got myself a Vanda cristata, it also tolerates low temperatures.
I'm a total nut case when it comes to knowledge about the climate in Pakistan - so take my advise with a grain of salt ;-)