Your gardenias have a phosphorus deficiency, at least that's what I see in the picture. You say they are brown. I see them as purplish. If they are purplish it is a phosphorus deficiency.

Have you had lots of rain or are they planted in acidic, clay or chalky soil. These often cause Phosphorus deficiency. Phosphorus is the second number on fertilizer boxes or bags. Fertilize with something that has a very high second number.

Have a look at the link below and see if they look like yours

Here is a link that might be useful: Phosphorus deficiency

Rather than add something you can't take away, can you have your soil tested for phosphorus deficiency? I'd hate to see you add something that your soil may not need at all.

The symptoms could also be caused by fertilizer burn (excess application), excess sun and heat, and other environmental stresses.

Thank you for your feedback. In Morocco it is rather difficult to get your soil tested, as it is not a common process. I tried to attach another picture but seem unable to . To me the leaf looks more brown than purple. I looked at the pictures on the web link you send but I do not recognize any purple in my gardenia leaf... but I could be wrong.
About fertilizer, I give it about once every 10-14 days (the box says once a week), and the plant get gets about 4 hours of direct sunlight a day, from 10:30 - 2:30 pmish. But it has been in the same location for 2 years, and last year it was fine. It is still growing baby leaves, but they are turning brown almost immediately.

All help to save my beloved gardenias is greatly appreciated. Thank you.

Gardenias need a consistent water supply. Check to see how moist or dry the soil is. Damage isn't classic insufficient low water, but I do think something is going on with the roots.

And I don't think it's low on phosphorus. (or any other nutrient.) Neither the damage pattern nor color matches up with that.

Aren't you having problems with your containerized citrus, as well? Or am I thinking of someone else?

Yes Rhizo, i also have a problem with my citrus tree. But the two are in two different gardens, each surrounded by other plants (which are fine).

any suggestions of what the problem may be?

Thank you

Well if it's not purpleish then do they look like these pictures. If they do then it is blight and you need a fungicide. Pick one that has this disease mentioned on the label.

Here is a link that might be useful: Bortrytis blight

oilpainter, don't you think that nihal should try to eliminate some environmental causes first? I mean, before the addition of phosphorus or fungicides or other chemicals?

The images I see don't seem to point to a disease, at least not to my eyes. I've never heard of a 'Camellia Blight' (Boyrytis) that affects the foliage. Petal blight is relatively common, but that's a whole different topic.

Oops, I meant GARDENIA, not camellia. Leaf tip necrosis is simply very typical of problems associated with the root/soil system of not only gardenias, but many other plants.

Over or under watering, inconsistent watering, too frequent fertilization in combination with dryish soils, etc are just a few of the environmental causes of plant symptoms just like what Nihal is observing.

Hello, just an update : my Gardenia died (not suprisingly!) but it's sister plants, which are planted in the same area and soil, seem to have picked up and look good (no buds though). I don't actually know what caused it, and admittedly I had to leave town for several weeks and when I got back, my plant had died. However I have decided to get a specialist to install an automatic sprinkling system, since I travel frequently and the staff have no knowledge of plant care, so do either over or under water. Hopefully this will help avoid these problems in the future.

My other Gardenia, in a different garden and potted (the others are planted in a very large build area) is looking splendid.
Thank you all for your help,
Nihal