I apologize, as I don't know what's wrong with your plant. I just wanted to comment that Calatheas are known to be fussy and a number of people find them difficult. Not to say you can't grow one, I'm just giving you a heads up.

Planto

Thank you for the heads up. This is really frustrating. I bought some Miracle-Gro today and feeded her a handful. Let's see what happens.

In the meantime any suggestions from anybody would be highly appreciated.

The more I look at it now, the more drooping I see.

Checked the roots as well and they seem to be white and plump. I don't know what to do really. :/

they often sell them in cachepot with inner plastic pot. yours look like it might be such a cachepot without a hole.
if it is - that can be the cause of your problem.
they need to be kept evenly moist but not wet. never allow it to completely dry out. so they are tricky to water.
any standing water that does not get absorbed within 15 min need to be removed - or else roots will start rotting.
they would do well in a self-watering pot.

This post was edited by petrushka on Wed, Apr 23, 14 at 16:11

To be honest, I am not an expert with Calatheas. But I own two and their "mood" is changing like the weather. Literally. So with absolute no reason they look droopy and and the next day they are happier than ever.
I found they don't like too much sun/heat. The leaves curl and have a dry feeling to them. Even if you think its not too sunny, it is.
And they like their soil dry out a bit between two waterings.
Thay also do the "praying thing" Marantas are famous for, though not every day, just when they feel like.
About yellowing leaves. Some of the older leaves simply died and new growth came. Couldn't find any reason for that.
I would say just let it be, don't panic. Don't overwater, leave it in the shade. They response in about 1-2 hours for a change in light conditions so you could maybe try a different spot?
Good luck :)

So I am posting a follow up picture as it just got to it's worst stage today as you can see. Drooping has gone to almost all the stems now and it's starting to get black spots and cracks on some leaves also.

Petrushka, the pot has numerous holes underneath it, I double checked it so it can't be that. I have also kept it moist at all times. Never too dry, never too wet and have been using filtered water from the first day.

MsGreenFinger thank you for your suggestion. I will try more sun today as I have it in a shade in a west/south facing room on a corner that is totally in shade. So I thought it would get enough light from the room. Maybe that will work... Fingers crossed.

Just don't put it in the window. West/South windows will be too hot for your Calathea if it receives direct sun afternoon sun. Near the window (maybe 2-3 away) is fine. Bright indirect with maybe a little morning sun is good for these.

Planto

What temperatures and humidity are you maintaining?

Calathea like it humid. Dry indoor air -- especially common for those of us in the northern regions over the winter -- is stressful to them.

They like it rather warm -- temps in the 70sF or up. Keep the plant away from cool drafts or from furnace/heater vents. Having chilly air or hot dry air blowing on it is not a happy situation.

Watering can be an issue. Depending upon where you live, watering may need to be adjusted throughout the year. If you keep your home cooler in winter the allow the plant to get a bit dry (not parched, not bone dry) between waterings. When temps are cooler, the plant slows down (so to speak) and does not need nor make use of as much water. Keeping it too wet at such a point, can result in root rot or even stem death due to bacteria or fungi. In the heat of summer, they can use more water and so can be kept damper.

As other have said, avoid direct sunlight -- bright indirect should be good.

Keep in mind too, that plants require time to adjust to new conditions. How much time and whether adjusting is even realistically possible depends on how radically different your conditions are from the original growers (not the BBS you may have purchased it from -- the REAL growers ... as in the nursery that supplies the BBS) as well as the type of plant itself (some plants are simply far more delicate than others). Constantly switching conditions as you seem to be doing -- while completely understandable -- can keep the plant in a constant state of stress.

Do not fertilize any more for a while! A stressed plant has enough issues to deal with. Fertilizer is not a "magic cure-all". It can actually make the situation worse.

What is the plant potted in?

The media in which most BBS plants are potted is usually -- to put it mildly -- absolute "crap." Typically the media is heavily or entirely peat based which means that it holds a great deal of water for a long time BUT once it dries out it tends to become hydrophobic (water repellant) meaning that it takes "forever" to remoisten. It is possible to have the outer ends/surfaces moist while the center of mass is completely dry.

Thank you so much for all the feedback Paul. I've gone step by step and adjusted all the conditions and now will wait patiently to see how my calathea reacts to its new environment.

I am based in London and we have had a fairly great spring so far. The temperature in the room does not go below 50-60F and the humidity in the room is also around 50% at all times.

What I have realised though was that the plant was sitting right next to a window higher on the wall close to the ceiling (I have it in a double height room) which I always had open for natural ventilation so now that is also closed and lesson learned.

I have tried a few things wishing it would react to one of them and hopefully get a little better so I could know what exactly the problem causing all the drooping was but now I will just wait for it to readjust as you also suggested... Roots checked to make sure there was no rotting, placed in a bright spot with no direct sunlight on, given some fertiliser (but no more), pebbled tray with loads of water inside for more moisture, no more watering until relatively dry etc etc.

The mixture indeed consists of quite a lot of peat but not entirely. I would say the ratio of soil and the peat is pretty decent for keeping the base moist enough for now from what I can see.

If the problem continues I will probably take it to the nursery closeby and see if they can help me out.

Again thank you so much for all your feedback and tips everyone. I will keep posting pictures of the progress soon.

mkk,
this is a very tropical plant. it should never be below 65F.
or it will suffer.
50F and even 60F is too low for this plant. it LIKES to be above 70F. it likes even MORE to be at 75F ;).
anything below 65F will slow down the water absorption considerably! at 60F it should be kept almost dry. root rot is very possible if soil is anything more then very-very slightly damp in low temps. allow it dry up may be half way down the pot. take a chopstick or bamboo skewer and sink it in all the way to the bottom (like for the cake test) - pull it out and you'll see where the moisture starts/ends and how moist is the skewer.
below 65F soil should never feel moist to touch . and that includes night temps.
put it in the warmest brightest no-sun place you have.

This post was edited by petrushka on Fri, Apr 25, 14 at 14:54

A Pebble tray w/ LOADS of water sounds like trouble.

It should NOT have loads of water, the water should only go to the top of the pebbles, so that the pot sits ON TOP of the pebbles touching the water. NOT IN THE WATER, which will rot your plant quickly! Just so you know.

I have one of these plants have had it since it was small it is now friving it's very healthy what I did was put it in a good potting mix and mist it everyday if possible feed it very lightly in spring and summer water it twice a week in warm areas and once a fortnight in winter do not let it get water logged empty saucer after 15 mins I hope this helps I'm in Australia.